/* 
 * tkTextBTree.c --
 *
 *	This file contains code that manages the B-tree representation
 *	of text for Tk's text widget and implements character and
 *	toggle segment types.
 *
 * Copyright (c) 1992-1994 The Regents of the University of California.
 * Copyright (c) 1994-1995 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tkTextBTree.c,v 1.4 1999/12/14 06:52:32 hobbs Exp $
 */

#include "tkInt.h"
#include "tkPort.h"
#include "tkText.h"

/*
 * The data structure below keeps summary information about one tag as part
 * of the tag information in a node.
 */

typedef struct Summary {
    TkTextTag *tagPtr;			/* Handle for tag. */
    int toggleCount;			/* Number of transitions into or
					 * out of this tag that occur in
					 * the subtree rooted at this node. */
    struct Summary *nextPtr;		/* Next in list of all tags for same
					 * node, or NULL if at end of list. */
} Summary;

/*
 * The data structure below defines a node in the B-tree.
 */

typedef struct Node {
    struct Node *parentPtr;		/* Pointer to parent node, or NULL if
					 * this is the root. */
    struct Node *nextPtr;		/* Next in list of siblings with the
					 * same parent node, or NULL for end
					 * of list. */
    Summary *summaryPtr;		/* First in malloc-ed list of info
					 * about tags in this subtree (NULL if
					 * no tag info in the subtree). */
    int level;				/* Level of this node in the B-tree.
					 * 0 refers to the bottom of the tree
					 * (children are lines, not nodes). */
    union {				/* First in linked list of children. */
	struct Node *nodePtr;		/* Used if level > 0. */
	TkTextLine *linePtr;		/* Used if level == 0. */
    } children;
    int numChildren;			/* Number of children of this node. */
    int numLines;			/* Total number of lines (leaves) in
					 * the subtree rooted here. */
} Node;

/*
 * Upper and lower bounds on how many children a node may have:
 * rebalance when either of these limits is exceeded.  MAX_CHILDREN
 * should be twice MIN_CHILDREN and MIN_CHILDREN must be >= 2.
 */

#define MAX_CHILDREN 12
#define MIN_CHILDREN 6

/*
 * The data structure below defines an entire B-tree.
 */

typedef struct BTree {
    Node *rootPtr;			/* Pointer to root of B-tree. */
    TkText *textPtr;			/* Used to find tagTable in consistency
					 * checking code */
} BTree;

/*
 * The structure below is used to pass information between
 * TkBTreeGetTags and IncCount:
 */

typedef struct TagInfo {
    int numTags;			/* Number of tags for which there
					 * is currently information in
					 * tags and counts. */
    int arraySize;			/* Number of entries allocated for
					 * tags and counts. */
    TkTextTag **tagPtrs;		/* Array of tags seen so far.
					 * Malloc-ed. */
    int *counts;			/* Toggle count (so far) for each
					 * entry in tags.  Malloc-ed. */
} TagInfo;

/*
 * Variable that indicates whether to enable consistency checks for
 * debugging.
 */

int tkBTreeDebug = 0;

/*
 * Macros that determine how much space to allocate for new segments:
 */

#define CSEG_SIZE(chars) ((unsigned) (Tk_Offset(TkTextSegment, body) \
	+ 1 + (chars)))
#define TSEG_SIZE ((unsigned) (Tk_Offset(TkTextSegment, body) \
	+ sizeof(TkTextToggle)))

/*
 * Forward declarations for procedures defined in this file:
 */

static void		ChangeNodeToggleCount _ANSI_ARGS_((Node *nodePtr,
			    TkTextTag *tagPtr, int delta));
static void		CharCheckProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr));
static int		CharDeleteProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr, int treeGone));
static TkTextSegment *	CharCleanupProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr));
static TkTextSegment *	CharSplitProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    int index));
static void		CheckNodeConsistency _ANSI_ARGS_((Node *nodePtr));
static void		CleanupLine _ANSI_ARGS_((TkTextLine *linePtr));
static void		DeleteSummaries _ANSI_ARGS_((Summary *tagPtr));
static void		DestroyNode _ANSI_ARGS_((Node *nodePtr));
static TkTextSegment *	FindTagEnd _ANSI_ARGS_((TkTextBTree tree, 
			    TkTextTag *tagPtr, TkTextIndex *indexPtr));
static void		IncCount _ANSI_ARGS_((TkTextTag *tagPtr, int inc,
			    TagInfo *tagInfoPtr));
static void		Rebalance _ANSI_ARGS_((BTree *treePtr, Node *nodePtr));
static void		RecomputeNodeCounts _ANSI_ARGS_((Node *nodePtr));
static TkTextSegment *	SplitSeg _ANSI_ARGS_((TkTextIndex *indexPtr));
static void		ToggleCheckProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr));
static TkTextSegment *	ToggleCleanupProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr));
static int		ToggleDeleteProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr, int treeGone));
static void		ToggleLineChangeProc _ANSI_ARGS_((TkTextSegment *segPtr,
			    TkTextLine *linePtr));
static TkTextSegment *	FindTagStart _ANSI_ARGS_((TkTextBTree tree,
			    TkTextTag *tagPtr, TkTextIndex *indexPtr));

/*
 * Type record for character segments:
 */

Tk_SegType tkTextCharType = {
    "character",				/* name */
    0,						/* leftGravity */
    CharSplitProc,				/* splitProc */
    CharDeleteProc,				/* deleteProc */
    CharCleanupProc,				/* cleanupProc */
    (Tk_SegLineChangeProc *) NULL,		/* lineChangeProc */
    TkTextCharLayoutProc,			/* layoutProc */
    CharCheckProc				/* checkProc */
};

/*
 * Type record for segments marking the beginning of a tagged
 * range:
 */

Tk_SegType tkTextToggleOnType = {
    "toggleOn",					/* name */
    0,						/* leftGravity */
    (Tk_SegSplitProc *) NULL,			/* splitProc */
    ToggleDeleteProc,				/* deleteProc */
    ToggleCleanupProc,				/* cleanupProc */
    ToggleLineChangeProc,			/* lineChangeProc */
    (Tk_SegLayoutProc *) NULL,			/* layoutProc */
    ToggleCheckProc				/* checkProc */
};

/*
 * Type record for segments marking the end of a tagged
 * range:
 */

Tk_SegType tkTextToggleOffType = {
    "toggleOff",				/* name */
    1,						/* leftGravity */
    (Tk_SegSplitProc *) NULL,			/* splitProc */
    ToggleDeleteProc,				/* deleteProc */
    ToggleCleanupProc,				/* cleanupProc */
    ToggleLineChangeProc,			/* lineChangeProc */
    (Tk_SegLayoutProc *) NULL,			/* layoutProc */
    ToggleCheckProc				/* checkProc */
};

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeCreate --
 *
 *	This procedure is called to create a new text B-tree.
 *
 * Results:
 *	The return value is a pointer to a new B-tree containing
 *	one line with nothing but a newline character.
 *
 * Side effects:
 *	Memory is allocated and initialized.
 *
 *----------------------------------------------------------------------
 */

TkTextBTree
TkBTreeCreate(textPtr)
    TkText *textPtr;
{
    register BTree *treePtr;
    register Node *rootPtr;
    register TkTextLine *linePtr, *linePtr2;
    register TkTextSegment *segPtr;

    /*
     * The tree will initially have two empty lines.  The second line
     * isn't actually part of the tree's contents, but its presence
     * makes several operations easier.  The tree will have one node,
     * which is also the root of the tree.
     */

    rootPtr = (Node *) ckalloc(sizeof(Node));
    linePtr = (TkTextLine *) ckalloc(sizeof(TkTextLine));
    linePtr2 = (TkTextLine *) ckalloc(sizeof(TkTextLine));
    rootPtr->parentPtr = NULL;
    rootPtr->nextPtr = NULL;
    rootPtr->summaryPtr = NULL;
    rootPtr->level = 0;
    rootPtr->children.linePtr = linePtr;
    rootPtr->numChildren = 2;
    rootPtr->numLines = 2;

    linePtr->parentPtr = rootPtr;
    linePtr->nextPtr = linePtr2;
    segPtr = (TkTextSegment *) ckalloc(CSEG_SIZE(1));
    linePtr->segPtr = segPtr;
    segPtr->typePtr = &tkTextCharType;
    segPtr->nextPtr = NULL;
    segPtr->size = 1;
    segPtr->body.chars[0] = '\n';
    segPtr->body.chars[1] = 0;

    linePtr2->parentPtr = rootPtr;
    linePtr2->nextPtr = NULL;
    segPtr = (TkTextSegment *) ckalloc(CSEG_SIZE(1));
    linePtr2->segPtr = segPtr;
    segPtr->typePtr = &tkTextCharType;
    segPtr->nextPtr = NULL;
    segPtr->size = 1;
    segPtr->body.chars[0] = '\n';
    segPtr->body.chars[1] = 0;

    treePtr = (BTree *) ckalloc(sizeof(BTree));
    treePtr->rootPtr = rootPtr;
    treePtr->textPtr = textPtr;

    return (TkTextBTree) treePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeDestroy --
 *
 *	Delete a B-tree, recycling all of the storage it contains.
 *
 * Results:
 *	The tree given by treePtr is deleted.  TreePtr should never
 *	again be used.
 *
 * Side effects:
 *	Memory is freed.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeDestroy(tree)
    TkTextBTree tree;			/* Pointer to tree to delete. */ 
{
    BTree *treePtr = (BTree *) tree;

    DestroyNode(treePtr->rootPtr);
    ckfree((char *) treePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * DestroyNode --
 *
 *	This is a recursive utility procedure used during the deletion
 *	of a B-tree.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	All the storage for nodePtr and its descendants is freed.
 *
 *----------------------------------------------------------------------
 */

static void
DestroyNode(nodePtr)
    register Node *nodePtr;
{
    if (nodePtr->level == 0) {
	TkTextLine *linePtr;
	TkTextSegment *segPtr;

	while (nodePtr->children.linePtr != NULL) {
	    linePtr = nodePtr->children.linePtr;
	    nodePtr->children.linePtr = linePtr->nextPtr;
	    while (linePtr->segPtr != NULL) {
		segPtr = linePtr->segPtr;
		linePtr->segPtr = segPtr->nextPtr;
		(*segPtr->typePtr->deleteProc)(segPtr, linePtr, 1);
	    }
	    ckfree((char *) linePtr);
	}
    } else {
	register Node *childPtr;

	while (nodePtr->children.nodePtr != NULL) {
	    childPtr = nodePtr->children.nodePtr;
	    nodePtr->children.nodePtr = childPtr->nextPtr;
	    DestroyNode(childPtr);
	}
    }
    DeleteSummaries(nodePtr->summaryPtr);
    ckfree((char *) nodePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * DeleteSummaries --
 *
 *	Free up all of the memory in a list of tag summaries associated
 *	with a node.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Storage is released.
 *
 *----------------------------------------------------------------------
 */

static void
DeleteSummaries(summaryPtr)
    register Summary *summaryPtr;	/* First in list of node's tag
					 * summaries. */
{
    register Summary *nextPtr;
    while (summaryPtr != NULL) {
	nextPtr = summaryPtr->nextPtr;
	ckfree((char *) summaryPtr);
	summaryPtr = nextPtr;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeInsertChars --
 *
 *	Insert characters at a given position in a B-tree.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Characters are added to the B-tree at the given position.
 *	If the string contains newlines, new lines will be added,
 *	which could cause the structure of the B-tree to change.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeInsertChars(indexPtr, string)
    register TkTextIndex *indexPtr;	/* Indicates where to insert text.
					 * When the procedure returns, this
					 * index is no longer valid because
					 * of changes to the segment
					 * structure. */
    char *string;			/* Pointer to bytes to insert (may
					 * contain newlines, must be null-
					 * terminated). */
{
    register Node *nodePtr;
    register TkTextSegment *prevPtr;	/* The segment just before the first
					 * new segment (NULL means new segment
					 * is at beginning of line). */
    TkTextSegment *curPtr;		/* Current segment;  new characters
					 * are inserted just after this one. 
					 * NULL means insert at beginning of
					 * line. */
    TkTextLine *linePtr;		/* Current line (new segments are
					 * added to this line). */
    register TkTextSegment *segPtr;
    TkTextLine *newLinePtr;
    int chunkSize;			/* # characters in current chunk. */
    register char *eol;			/* Pointer to character just after last
					 * one in current chunk. */
    int changeToLineCount;		/* Counts change to total number of
					 * lines in file. */

    prevPtr = SplitSeg(indexPtr);
    linePtr = indexPtr->linePtr;
    curPtr = prevPtr;

    /*
     * Chop the string up into lines and create a new segment for
     * each line, plus a new line for the leftovers from the
     * previous line.
     */

    changeToLineCount = 0;
    while (*string != 0) {
	for (eol = string; *eol != 0; eol++) {
	    if (*eol == '\n') {
		eol++;
		break;
	    }
	}
	chunkSize = eol-string;
	segPtr = (TkTextSegment *) ckalloc(CSEG_SIZE(chunkSize));
	segPtr->typePtr = &tkTextCharType;
	if (curPtr == NULL) {
	    segPtr->nextPtr = linePtr->segPtr;
	    linePtr->segPtr = segPtr;
	} else {
	    segPtr->nextPtr = curPtr->nextPtr;
	    curPtr->nextPtr = segPtr;
	}
	segPtr->size = chunkSize;
	strncpy(segPtr->body.chars, string, (size_t) chunkSize);
	segPtr->body.chars[chunkSize] = 0;

	if (eol[-1] != '\n') {
	    break;
	}

	/*
	 * The chunk ended with a newline, so create a new TkTextLine
	 * and move the remainder of the old line to it.
	 */

	newLinePtr = (TkTextLine *) ckalloc(sizeof(TkTextLine));
	newLinePtr->parentPtr = linePtr->parentPtr;
	newLinePtr->nextPtr = linePtr->nextPtr;
	linePtr->nextPtr = newLinePtr;
	newLinePtr->segPtr = segPtr->nextPtr;
	segPtr->nextPtr = NULL;
	linePtr = newLinePtr;
	curPtr = NULL;
	changeToLineCount++;

	string = eol;
    }

    /*
     * Cleanup the starting line for the insertion, plus the ending
     * line if it's different.
     */

    CleanupLine(indexPtr->linePtr);
    if (linePtr != indexPtr->linePtr) {
	CleanupLine(linePtr);
    }

    /*
     * Increment the line counts in all the parent nodes of the insertion
     * point, then rebalance the tree if necessary.
     */

    for (nodePtr = linePtr->parentPtr ; nodePtr != NULL;
	    nodePtr = nodePtr->parentPtr) {
	nodePtr->numLines += changeToLineCount;
    }
    nodePtr = linePtr->parentPtr;
    nodePtr->numChildren += changeToLineCount;
    if (nodePtr->numChildren > MAX_CHILDREN) {
	Rebalance((BTree *) indexPtr->tree, nodePtr);
    }

    if (tkBTreeDebug) {
	TkBTreeCheck(indexPtr->tree);
    }
}

/*
 *--------------------------------------------------------------
 *
 * SplitSeg --
 *
 *	This procedure is called before adding or deleting
 *	segments.  It does three things: (a) it finds the segment
 *	containing indexPtr;  (b) if there are several such
 *	segments (because some segments have zero length) then
 *	it picks the first segment that does not have left
 *	gravity;  (c) if the index refers to the middle of
 *	a segment then it splits the segment so that the
 *	index now refers to the beginning of a segment.
 *
 * Results:
 *	The return value is a pointer to the segment just
 *	before the segment corresponding to indexPtr (as
 *	described above).  If the segment corresponding to
 *	indexPtr is the first in its line then the return
 *	value is NULL.
 *
 * Side effects:
 *	The segment referred to by indexPtr is split unless
 *	indexPtr refers to its first character.
 *
 *--------------------------------------------------------------
 */

static TkTextSegment *
SplitSeg(indexPtr)
    TkTextIndex *indexPtr;		/* Index identifying position
					 * at which to split a segment. */
{
    TkTextSegment *prevPtr, *segPtr;
    int count;

    for (count = indexPtr->byteIndex, prevPtr = NULL,
	    segPtr = indexPtr->linePtr->segPtr; segPtr != NULL;
	    count -= segPtr->size, prevPtr = segPtr, segPtr = segPtr->nextPtr) {
	if (segPtr->size > count) {
	    if (count == 0) {
		return prevPtr;
	    }
	    segPtr = (*segPtr->typePtr->splitProc)(segPtr, count);
	    if (prevPtr == NULL) {
		indexPtr->linePtr->segPtr = segPtr;
	    } else {
		prevPtr->nextPtr = segPtr;
	    }
	    return segPtr;
	} else if ((segPtr->size == 0) && (count == 0)
		&& !segPtr->typePtr->leftGravity) {
	    return prevPtr;
	}
    }
    panic("SplitSeg reached end of line!");
    return NULL;
}

/*
 *--------------------------------------------------------------
 *
 * CleanupLine --
 *
 *	This procedure is called after modifications have been
 *	made to a line.  It scans over all of the segments in
 *	the line, giving each a chance to clean itself up, e.g.
 *	by merging with the following segments, updating internal
 *	information, etc.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Depends on what the segment-specific cleanup procedures do.
 *
 *--------------------------------------------------------------
 */

static void
CleanupLine(linePtr)
    TkTextLine *linePtr;		/* Line to be cleaned up. */
{
    TkTextSegment *segPtr, **prevPtrPtr;
    int anyChanges;

    /*
     * Make a pass over all of the segments in the line, giving each
     * a chance to clean itself up.  This could potentially change
     * the structure of the line, e.g. by merging two segments
     * together or having two segments cancel themselves;  if so,
     * then repeat the whole process again, since the first structure
     * change might make other structure changes possible.  Repeat
     * until eventually there are no changes.
     */

    while (1) {
	anyChanges = 0;
	for (prevPtrPtr = &linePtr->segPtr, segPtr = *prevPtrPtr;
		segPtr != NULL;
		prevPtrPtr = &(*prevPtrPtr)->nextPtr, segPtr = *prevPtrPtr) {
	    if (segPtr->typePtr->cleanupProc != NULL) {
		*prevPtrPtr = (*segPtr->typePtr->cleanupProc)(segPtr, linePtr);
		if (segPtr != *prevPtrPtr) {
		    anyChanges = 1;
		}
	    }
	}
	if (!anyChanges) {
	    break;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeDeleteChars --
 *
 *	Delete a range of characters from a B-tree.  The caller
 *	must make sure that the final newline of the B-tree is
 *	never deleted.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Information is deleted from the B-tree.  This can cause the
 *	internal structure of the B-tree to change.  Note: because
 *	of changes to the B-tree structure, the indices pointed
 *	to by index1Ptr and index2Ptr should not be used after this
 *	procedure returns.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeDeleteChars(index1Ptr, index2Ptr)
    register TkTextIndex *index1Ptr;	/* Indicates first character that is
					 * to be deleted. */
    register TkTextIndex *index2Ptr;	/* Indicates character just after the
					 * last one that is to be deleted. */
{
    TkTextSegment *prevPtr;		/* The segment just before the start
					 * of the deletion range. */
    TkTextSegment *lastPtr;		/* The segment just after the end
					 * of the deletion range. */
    TkTextSegment *segPtr, *nextPtr;
    TkTextLine *curLinePtr;
    Node *curNodePtr, *nodePtr;

    /*
     * Tricky point:  split at index2Ptr first;  otherwise the split
     * at index2Ptr may invalidate segPtr and/or prevPtr.
     */

    lastPtr = SplitSeg(index2Ptr);
    if (lastPtr != NULL) {
	lastPtr = lastPtr->nextPtr;
    }  else {
	lastPtr = index2Ptr->linePtr->segPtr;
    }
    prevPtr = SplitSeg(index1Ptr);
    if (prevPtr != NULL) {
	segPtr = prevPtr->nextPtr;
	prevPtr->nextPtr = lastPtr;
    } else {
	segPtr = index1Ptr->linePtr->segPtr;
	index1Ptr->linePtr->segPtr = lastPtr;
    }

    /*
     * Delete all of the segments between prevPtr and lastPtr.
     */

    curLinePtr = index1Ptr->linePtr;
    curNodePtr = curLinePtr->parentPtr;
    while (segPtr != lastPtr) {
	if (segPtr == NULL) {
	    TkTextLine *nextLinePtr;

	    /*
	     * We just ran off the end of a line.  First find the
	     * next line, then go back to the old line and delete it
	     * (unless it's the starting line for the range).
	     */

	    nextLinePtr = TkBTreeNextLine(curLinePtr);
	    if (curLinePtr != index1Ptr->linePtr) {
		if (curNodePtr == index1Ptr->linePtr->parentPtr) {
		    index1Ptr->linePtr->nextPtr = curLinePtr->nextPtr;
		} else {
		    curNodePtr->children.linePtr = curLinePtr->nextPtr;
		}
		for (nodePtr = curNodePtr; nodePtr != NULL;
			nodePtr = nodePtr->parentPtr) {
		    nodePtr->numLines--;
		}
		curNodePtr->numChildren--;
		ckfree((char *) curLinePtr);
	    }
	    curLinePtr = nextLinePtr;
	    segPtr = curLinePtr->segPtr;

	    /*
	     * If the node is empty then delete it and its parents,
	     * recursively upwards until a non-empty node is found.
	     */

	    while (curNodePtr->numChildren == 0) {
		Node *parentPtr;

		parentPtr = curNodePtr->parentPtr;
		if (parentPtr->children.nodePtr == curNodePtr) {
		    parentPtr->children.nodePtr = curNodePtr->nextPtr;
		} else {
		    Node *prevNodePtr = parentPtr->children.nodePtr;
		    while (prevNodePtr->nextPtr != curNodePtr) {
			prevNodePtr = prevNodePtr->nextPtr;
		    }
		    prevNodePtr->nextPtr = curNodePtr->nextPtr;
		}
		parentPtr->numChildren--;
		ckfree((char *) curNodePtr);
		curNodePtr = parentPtr;
	    }
	    curNodePtr = curLinePtr->parentPtr;
	    continue;
	}

	nextPtr = segPtr->nextPtr;
	if ((*segPtr->typePtr->deleteProc)(segPtr, curLinePtr, 0) != 0) {
	    /*
	     * This segment refuses to die.  Move it to prevPtr and
	     * advance prevPtr if the segment has left gravity.
	     */

	    if (prevPtr == NULL) {
		segPtr->nextPtr = index1Ptr->linePtr->segPtr;
		index1Ptr->linePtr->segPtr = segPtr;
	    } else {
		segPtr->nextPtr = prevPtr->nextPtr;
		prevPtr->nextPtr = segPtr;
	    }
	    if (segPtr->typePtr->leftGravity) {
		prevPtr = segPtr;
	    }
	}
	segPtr = nextPtr;
    }

    /*
     * If the beginning and end of the deletion range are in different
     * lines, join the two lines together and discard the ending line.
     */

    if (index1Ptr->linePtr != index2Ptr->linePtr) {
	TkTextLine *prevLinePtr;

	for (segPtr = lastPtr; segPtr != NULL;
		segPtr = segPtr->nextPtr) {
	    if (segPtr->typePtr->lineChangeProc != NULL) {
		(*segPtr->typePtr->lineChangeProc)(segPtr, index2Ptr->linePtr);
	    }
	}
	curNodePtr = index2Ptr->linePtr->parentPtr;
	for (nodePtr = curNodePtr; nodePtr != NULL;
		nodePtr = nodePtr->parentPtr) {
	    nodePtr->numLines--;
	}
	curNodePtr->numChildren--;
	prevLinePtr = curNodePtr->children.linePtr;
	if (prevLinePtr == index2Ptr->linePtr) {
	    curNodePtr->children.linePtr = index2Ptr->linePtr->nextPtr;
	} else {
	    while (prevLinePtr->nextPtr != index2Ptr->linePtr) {
		prevLinePtr = prevLinePtr->nextPtr;
	    }
	    prevLinePtr->nextPtr = index2Ptr->linePtr->nextPtr;
	}
	ckfree((char *) index2Ptr->linePtr);
	Rebalance((BTree *) index2Ptr->tree, curNodePtr);
    }

    /*
     * Cleanup the segments in the new line.
     */

    CleanupLine(index1Ptr->linePtr);

    /*
     * Lastly, rebalance the first node of the range.
     */

    Rebalance((BTree *) index1Ptr->tree, index1Ptr->linePtr->parentPtr);
    if (tkBTreeDebug) {
	TkBTreeCheck(index1Ptr->tree);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeFindLine --
 *
 *	Find a particular line in a B-tree based on its line number.
 *
 * Results:
 *	The return value is a pointer to the line structure for the
 *	line whose index is "line", or NULL if no such line exists.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

TkTextLine *
TkBTreeFindLine(tree, line)
    TkTextBTree tree;			/* B-tree in which to find line. */
    int line;				/* Index of desired line. */
{
    BTree *treePtr = (BTree *) tree;
    register Node *nodePtr;
    register TkTextLine *linePtr;
    int linesLeft;

    nodePtr = treePtr->rootPtr;
    linesLeft = line;
    if ((line < 0) || (line >= nodePtr->numLines)) {
	return NULL;
    }

    /*
     * Work down through levels of the tree until a node is found at
     * level 0.
     */

    while (nodePtr->level != 0) {
	for (nodePtr = nodePtr->children.nodePtr;
		nodePtr->numLines <= linesLeft;
		nodePtr = nodePtr->nextPtr) {
	    if (nodePtr == NULL) {
		panic("TkBTreeFindLine ran out of nodes");
	    }
	    linesLeft -= nodePtr->numLines;
	}
    }

    /*
     * Work through the lines attached to the level-0 node.
     */

    for (linePtr = nodePtr->children.linePtr; linesLeft > 0;
	    linePtr = linePtr->nextPtr) {
	if (linePtr == NULL) {
	    panic("TkBTreeFindLine ran out of lines");
	}
	linesLeft -= 1;
    }
    return linePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeNextLine --
 *
 *	Given an existing line in a B-tree, this procedure locates the
 *	next line in the B-tree.  This procedure is used for scanning
 *	through the B-tree.
 *
 * Results:
 *	The return value is a pointer to the line that immediately
 *	follows linePtr, or NULL if there is no such line.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

TkTextLine *
TkBTreeNextLine(linePtr)
    register TkTextLine *linePtr;	/* Pointer to existing line in
					 * B-tree. */
{
    register Node *nodePtr;

    if (linePtr->nextPtr != NULL) {
	return linePtr->nextPtr;
    }

    /*
     * This was the last line associated with the particular parent node.
     * Search up the tree for the next node, then search down from that
     * node to find the first line.
     */

    for (nodePtr = linePtr->parentPtr; ; nodePtr = nodePtr->parentPtr) {
	if (nodePtr->nextPtr != NULL) {
	    nodePtr = nodePtr->nextPtr;
	    break;
	}
	if (nodePtr->parentPtr == NULL) {
	    return (TkTextLine *) NULL;
	}
    }
    while (nodePtr->level > 0) {
	nodePtr = nodePtr->children.nodePtr;
    }
    return nodePtr->children.linePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreePreviousLine --
 *
 *	Given an existing line in a B-tree, this procedure locates the
 *	previous line in the B-tree.  This procedure is used for scanning
 *	through the B-tree in the reverse direction.
 *
 * Results:
 *	The return value is a pointer to the line that immediately
 *	preceeds linePtr, or NULL if there is no such line.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

TkTextLine *
TkBTreePreviousLine(linePtr)
    register TkTextLine *linePtr;	/* Pointer to existing line in
					 * B-tree. */
{
    register Node *nodePtr;
    register Node *node2Ptr;
    register TkTextLine *prevPtr;

    /*
     * Find the line under this node just before the starting line.
     */
    prevPtr = linePtr->parentPtr->children.linePtr;	/* First line at leaf */
    while (prevPtr != linePtr) {
	if (prevPtr->nextPtr == linePtr) {
	    return prevPtr;
	}
	prevPtr = prevPtr->nextPtr;
	if (prevPtr == (TkTextLine *) NULL) {
	    panic("TkBTreePreviousLine ran out of lines");
	}
    }

    /*
     * This was the first line associated with the particular parent node.
     * Search up the tree for the previous node, then search down from that
     * node to find its last line.
     */
    for (nodePtr = linePtr->parentPtr; ; nodePtr = nodePtr->parentPtr) {
	if (nodePtr == (Node *) NULL || nodePtr->parentPtr == (Node *) NULL) {
	    return (TkTextLine *) NULL;
	}
	if (nodePtr != nodePtr->parentPtr->children.nodePtr) {
	    break;
	}
    }
    for (node2Ptr = nodePtr->parentPtr->children.nodePtr; ; 
	    node2Ptr = node2Ptr->children.nodePtr) {
	while (node2Ptr->nextPtr != nodePtr) {
	    node2Ptr = node2Ptr->nextPtr;
	}
	if (node2Ptr->level == 0) {
	    break;
	}
	nodePtr = (Node *)NULL;
    }
    for (prevPtr = node2Ptr->children.linePtr ; ; prevPtr = prevPtr->nextPtr) {
	if (prevPtr->nextPtr == (TkTextLine *) NULL) {
	    return prevPtr;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeLineIndex --
 *
 *	Given a pointer to a line in a B-tree, return the numerical
 *	index of that line.
 *
 * Results:
 *	The result is the index of linePtr within the tree, where 0
 *	corresponds to the first line in the tree.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
TkBTreeLineIndex(linePtr)
    TkTextLine *linePtr;		/* Pointer to existing line in
					 * B-tree. */
{
    register TkTextLine *linePtr2;
    register Node *nodePtr, *parentPtr, *nodePtr2;
    int index;

    /*
     * First count how many lines precede this one in its level-0
     * node.
     */

    nodePtr = linePtr->parentPtr;
    index = 0;
    for (linePtr2 = nodePtr->children.linePtr; linePtr2 != linePtr;
	    linePtr2 = linePtr2->nextPtr) {
	if (linePtr2 == NULL) {
	    panic("TkBTreeLineIndex couldn't find line");
	}
	index += 1;
    }

    /*
     * Now work up through the levels of the tree one at a time,
     * counting how many lines are in nodes preceding the current
     * node.
     */

    for (parentPtr = nodePtr->parentPtr ; parentPtr != NULL;
	    nodePtr = parentPtr, parentPtr = parentPtr->parentPtr) {
	for (nodePtr2 = parentPtr->children.nodePtr; nodePtr2 != nodePtr;
		nodePtr2 = nodePtr2->nextPtr) {
	    if (nodePtr2 == NULL) {
		panic("TkBTreeLineIndex couldn't find node");
	    }
	    index += nodePtr2->numLines;
	}
    }
    return index;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeLinkSegment --
 *
 *	This procedure adds a new segment to a B-tree at a given
 *	location.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	SegPtr will be linked into its tree.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
void
TkBTreeLinkSegment(segPtr, indexPtr)
    TkTextSegment *segPtr;	/* Pointer to new segment to be added to
				 * B-tree.  Should be completely initialized
				 * by caller except for nextPtr field. */
    TkTextIndex *indexPtr;	/* Where to add segment:  it gets linked
				 * in just before the segment indicated
				 * here. */
{
    register TkTextSegment *prevPtr;

    prevPtr = SplitSeg(indexPtr);
    if (prevPtr == NULL) {
	segPtr->nextPtr = indexPtr->linePtr->segPtr;
	indexPtr->linePtr->segPtr = segPtr;
    } else {
	segPtr->nextPtr = prevPtr->nextPtr;
	prevPtr->nextPtr = segPtr;
    }
    CleanupLine(indexPtr->linePtr);
    if (tkBTreeDebug) {
	TkBTreeCheck(indexPtr->tree);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeUnlinkSegment --
 *
 *	This procedure unlinks a segment from its line in a B-tree.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	SegPtr will be unlinked from linePtr.  The segment itself
 *	isn't modified by this procedure.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
void
TkBTreeUnlinkSegment(tree, segPtr, linePtr)
    TkTextBTree tree;			/* Tree containing segment. */
    TkTextSegment *segPtr;		/* Segment to be unlinked. */
    TkTextLine *linePtr;		/* Line that currently contains
					 * segment. */
{
    register TkTextSegment *prevPtr;

    if (linePtr->segPtr == segPtr) {
	linePtr->segPtr = segPtr->nextPtr;
    } else {
	for (prevPtr = linePtr->segPtr; prevPtr->nextPtr != segPtr;
		prevPtr = prevPtr->nextPtr) {
	    /* Empty loop body. */
	}
	prevPtr->nextPtr = segPtr->nextPtr;
    }
    CleanupLine(linePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeTag --
 *
 *	Turn a given tag on or off for a given range of characters in
 *	a B-tree of text.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The given tag is added to the given range of characters
 *	in the tree or removed from all those characters, depending
 *	on the "add" argument.  The structure of the btree is modified
 *	enough that index1Ptr and index2Ptr are no longer valid after
 *	this procedure returns, and the indexes may be modified by
 *	this procedure.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeTag(index1Ptr, index2Ptr, tagPtr, add)
    register TkTextIndex *index1Ptr;	/* Indicates first character in
					 * range. */
    register TkTextIndex *index2Ptr;	/* Indicates character just after the
					 * last one in range. */
    TkTextTag *tagPtr;			/* Tag to add or remove. */
    int add;				/* One means add tag to the given
					 * range of characters;  zero means
					 * remove the tag from the range. */
{
    TkTextSegment *segPtr, *prevPtr;
    TkTextSearch search;
    TkTextLine *cleanupLinePtr;
    int oldState;
    int changed;

    /*
     * See whether the tag is present at the start of the range.  If
     * the state doesn't already match what we want then add a toggle
     * there.
     */

    oldState = TkBTreeCharTagged(index1Ptr, tagPtr);
    if ((add != 0) ^ oldState) {
	segPtr = (TkTextSegment *) ckalloc(TSEG_SIZE);
	segPtr->typePtr = (add) ? &tkTextToggleOnType : &tkTextToggleOffType;
	prevPtr = SplitSeg(index1Ptr);
	if (prevPtr == NULL) {
	    segPtr->nextPtr = index1Ptr->linePtr->segPtr;
	    index1Ptr->linePtr->segPtr = segPtr;
	} else {
	    segPtr->nextPtr = prevPtr->nextPtr;
	    prevPtr->nextPtr = segPtr;
	}
	segPtr->size = 0;
	segPtr->body.toggle.tagPtr = tagPtr;
	segPtr->body.toggle.inNodeCounts = 0;
    }

    /*
     * Scan the range of characters and delete any internal tag
     * transitions.  Keep track of what the old state was at the end
     * of the range, and add a toggle there if it's needed.
     */

    TkBTreeStartSearch(index1Ptr, index2Ptr, tagPtr, &search);
    cleanupLinePtr = index1Ptr->linePtr;
    while (TkBTreeNextTag(&search)) {
	oldState ^= 1;
	segPtr = search.segPtr;
	prevPtr = search.curIndex.linePtr->segPtr;
	if (prevPtr == segPtr) {
	    search.curIndex.linePtr->segPtr = segPtr->nextPtr;
	} else {
	    while (prevPtr->nextPtr != segPtr) {
		prevPtr = prevPtr->nextPtr;
	    }
	    prevPtr->nextPtr = segPtr->nextPtr;
	}
	if (segPtr->body.toggle.inNodeCounts) {
	    ChangeNodeToggleCount(search.curIndex.linePtr->parentPtr,
		    segPtr->body.toggle.tagPtr, -1);
	    segPtr->body.toggle.inNodeCounts = 0;
	    changed = 1;
	} else {
	    changed = 0;
	}
	ckfree((char *) segPtr);

	/*
	 * The code below is a bit tricky.  After deleting a toggle
	 * we eventually have to call CleanupLine, in order to allow
	 * character segments to be merged together.  To do this, we
	 * remember in cleanupLinePtr a line that needs to be
	 * cleaned up, but we don't clean it up until we've moved
	 * on to a different line.  That way the cleanup process
	 * won't goof up segPtr.
	 */

	if (cleanupLinePtr != search.curIndex.linePtr) {
	    CleanupLine(cleanupLinePtr);
	    cleanupLinePtr = search.curIndex.linePtr;
	}
	/*
	 * Quick hack.  ChangeNodeToggleCount may move the tag's root
	 * location around and leave the search in the void.  This resets
	 * the search.
	 */
	if (changed) {
	    TkBTreeStartSearch(index1Ptr, index2Ptr, tagPtr, &search);
	}
    }
    if ((add != 0) ^ oldState) {
	segPtr = (TkTextSegment *) ckalloc(TSEG_SIZE);
	segPtr->typePtr = (add) ? &tkTextToggleOffType : &tkTextToggleOnType;
	prevPtr = SplitSeg(index2Ptr);
	if (prevPtr == NULL) {
	    segPtr->nextPtr = index2Ptr->linePtr->segPtr;
	    index2Ptr->linePtr->segPtr = segPtr;
	} else {
	    segPtr->nextPtr = prevPtr->nextPtr;
	    prevPtr->nextPtr = segPtr;
	}
	segPtr->size = 0;
	segPtr->body.toggle.tagPtr = tagPtr;
	segPtr->body.toggle.inNodeCounts = 0;
    }

    /*
     * Cleanup cleanupLinePtr and the last line of the range, if
     * these are different.
     */

    CleanupLine(cleanupLinePtr);
    if (cleanupLinePtr != index2Ptr->linePtr) {
	CleanupLine(index2Ptr->linePtr);
    }

    if (tkBTreeDebug) {
	TkBTreeCheck(index1Ptr->tree);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ChangeNodeToggleCount --
 *
 *	This procedure increments or decrements the toggle count for
 *	a particular tag in a particular node and all its ancestors
 *	up to the per-tag root node.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The toggle count for tag is adjusted up or down by "delta" in
 *	nodePtr.  This routine maintains the tagRootPtr that identifies
 *	the root node for the tag, moving it up or down the tree as needed.
 *
 *----------------------------------------------------------------------
 */

static void
ChangeNodeToggleCount(nodePtr, tagPtr, delta)
    register Node *nodePtr;		/* Node whose toggle count for a tag
					 * must be changed. */
    TkTextTag *tagPtr;			/* Information about tag. */
    int delta;				/* Amount to add to current toggle
					 * count for tag (may be negative). */
{
    register Summary *summaryPtr, *prevPtr;
    register Node *node2Ptr;
    int rootLevel;			/* Level of original tag root */

    tagPtr->toggleCount += delta;
    if (tagPtr->tagRootPtr == (Node *) NULL) {
	tagPtr->tagRootPtr = nodePtr;
	return;
    }

    /*
     * Note the level of the existing root for the tag so we can detect
     * if it needs to be moved because of the toggle count change.
     */

    rootLevel = tagPtr->tagRootPtr->level;

    /*
     * Iterate over the node and its ancestors up to the tag root, adjusting
     * summary counts at each node and moving the tag's root upwards if
     * necessary.
     */

    for ( ; nodePtr != tagPtr->tagRootPtr; nodePtr = nodePtr->parentPtr) {
	/*
	 * See if there's already an entry for this tag for this node.  If so,
	 * perhaps all we have to do is adjust its count.
	 */
    
	for (prevPtr = NULL, summaryPtr = nodePtr->summaryPtr;
		summaryPtr != NULL;
		prevPtr = summaryPtr, summaryPtr = summaryPtr->nextPtr) {
	    if (summaryPtr->tagPtr == tagPtr) {
		break;
	    }
	}
	if (summaryPtr != NULL) {
	    summaryPtr->toggleCount += delta;
	    if (summaryPtr->toggleCount > 0 &&
		    summaryPtr->toggleCount < tagPtr->toggleCount) {
		continue;
	    }
	    if (summaryPtr->toggleCount != 0) {
		/*
		 * Should never find a node with max toggle count at this
		 * point (there shouldn't have been a summary entry in the
		 * first place).
		 */

		panic("ChangeNodeToggleCount: bad toggle count (%d) max (%d)",
		    summaryPtr->toggleCount, tagPtr->toggleCount);
	    }
    
	    /*
	     * Zero toggle count;  must remove this tag from the list.
	     */

	    if (prevPtr == NULL) {
		nodePtr->summaryPtr = summaryPtr->nextPtr;
	    } else {
		prevPtr->nextPtr = summaryPtr->nextPtr;
	    }
	    ckfree((char *) summaryPtr);
	} else {
	    /*
	     * This tag isn't currently in the summary information list.
	     */
    
	    if (rootLevel == nodePtr->level) {
    
		/*
		 * The old tag root is at the same level in the tree as this
		 * node, but it isn't at this node.  Move the tag root up
		 * a level, in the hopes that it will now cover this node
		 * as well as the old root (if not, we'll move it up again
		 * the next time through the loop).  To push it up one level
		 * we copy the original toggle count into the summary
		 * information at the old root and change the root to its
		 * parent node.
		 */
    
		Node *rootNodePtr = tagPtr->tagRootPtr;
		summaryPtr = (Summary *) ckalloc(sizeof(Summary));
		summaryPtr->tagPtr = tagPtr;
		summaryPtr->toggleCount = tagPtr->toggleCount - delta;
		summaryPtr->nextPtr = rootNodePtr->summaryPtr;
		rootNodePtr->summaryPtr = summaryPtr;
		rootNodePtr = rootNodePtr->parentPtr;
		rootLevel = rootNodePtr->level;
		tagPtr->tagRootPtr = rootNodePtr;
	    }
	    summaryPtr = (Summary *) ckalloc(sizeof(Summary));
	    summaryPtr->tagPtr = tagPtr;
	    summaryPtr->toggleCount = delta;
	    summaryPtr->nextPtr = nodePtr->summaryPtr;
	    nodePtr->summaryPtr = summaryPtr;
	}
    }

    /*
     * If we've decremented the toggle count, then it may be necessary
     * to push the tag root down one or more levels.
     */

    if (delta >= 0) {
	return;
    }
    if (tagPtr->toggleCount == 0) {
	tagPtr->tagRootPtr = (Node *) NULL;
	return;
    }
    nodePtr = tagPtr->tagRootPtr;
    while (nodePtr->level > 0) {
	/*
	 * See if a single child node accounts for all of the tag's
	 * toggles.  If so, push the root down one level.
	 */

	for (node2Ptr = nodePtr->children.nodePtr;
		node2Ptr != (Node *)NULL ;
		node2Ptr = node2Ptr->nextPtr) {
	    for (prevPtr = NULL, summaryPtr = node2Ptr->summaryPtr;
		    summaryPtr != NULL;
		    prevPtr = summaryPtr, summaryPtr = summaryPtr->nextPtr) {
		if (summaryPtr->tagPtr == tagPtr) {
		    break;
		}
	    }
	    if (summaryPtr == NULL) {
		continue;
	    }
	    if (summaryPtr->toggleCount != tagPtr->toggleCount) {
		/*
		 * No node has all toggles, so the root is still valid.
		 */

		return;
	    }

	    /*
	     * This node has all the toggles, so push down the root.
	     */

	    if (prevPtr == NULL) {
		node2Ptr->summaryPtr = summaryPtr->nextPtr;
	    } else {
		prevPtr->nextPtr = summaryPtr->nextPtr;
	    }
	    ckfree((char *) summaryPtr);
	    tagPtr->tagRootPtr = node2Ptr;
	    break;
	}
	nodePtr = tagPtr->tagRootPtr;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * FindTagStart --
 *
 *	Find the start of the first range of a tag.
 *
 * Results:
 *	The return value is a pointer to the first tag toggle segment
 *	for the tag.  This can be either a tagon or tagoff segments because
 *	of the way TkBTreeAdd removes a tag.
 *	Sets *indexPtr to be the index of the tag toggle.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static TkTextSegment *
FindTagStart(tree, tagPtr, indexPtr)
    TkTextBTree tree;			/* Tree to search within */
    TkTextTag *tagPtr;			/* Tag to search for. */
    TkTextIndex *indexPtr;		/* Return - index information */
{
    register Node *nodePtr;
    register TkTextLine *linePtr;
    register TkTextSegment *segPtr;
    register Summary *summaryPtr;
    int offset;

    nodePtr = tagPtr->tagRootPtr;
    if (nodePtr == (Node *) NULL) {
	return NULL;
    }

    /*
     * Search from the root of the subtree that contains the tag down
     * to the level 0 node.
     */

    while (nodePtr->level > 0) {
	for (nodePtr = nodePtr->children.nodePtr ; nodePtr != (Node *) NULL;
		nodePtr = nodePtr->nextPtr) {
	    for (summaryPtr = nodePtr->summaryPtr ; summaryPtr != NULL;
		    summaryPtr = summaryPtr->nextPtr) {
		if (summaryPtr->tagPtr == tagPtr) {
		    goto gotNodeWithTag;
		}
	    }
	}
	gotNodeWithTag:
	continue;
    }

    /*
     * Work through the lines attached to the level-0 node.
     */

    for (linePtr = nodePtr->children.linePtr; linePtr != (TkTextLine *) NULL;
	    linePtr = linePtr->nextPtr) {
	for (offset = 0, segPtr = linePtr->segPtr ; segPtr != NULL;
		offset += segPtr->size, segPtr = segPtr->nextPtr) {
	    if (((segPtr->typePtr == &tkTextToggleOnType)
		    || (segPtr->typePtr == &tkTextToggleOffType))
		    && (segPtr->body.toggle.tagPtr == tagPtr)) {
		/*
		 * It is possible that this is a tagoff tag, but that
		 * gets cleaned up later.
		 */
		indexPtr->tree = tree;
		indexPtr->linePtr = linePtr;
		indexPtr->byteIndex = offset;
		return segPtr;
	    }
	}
    }
    return NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * FindTagEnd --
 *
 *	Find the end of the last range of a tag.
 *
 * Results:
 *	The return value is a pointer to the last tag toggle segment
 *	for the tag.  This can be either a tagon or tagoff segments because
 *	of the way TkBTreeAdd removes a tag.
 *	Sets *indexPtr to be the index of the tag toggle.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static TkTextSegment *
FindTagEnd(tree, tagPtr, indexPtr)
    TkTextBTree tree;			/* Tree to search within */
    TkTextTag *tagPtr;			/* Tag to search for. */
    TkTextIndex *indexPtr;		/* Return - index information */
{
    register Node *nodePtr, *lastNodePtr;
    register TkTextLine *linePtr ,*lastLinePtr;
    register TkTextSegment *segPtr, *lastSegPtr, *last2SegPtr;
    register Summary *summaryPtr;
    int lastoffset, lastoffset2, offset;

    nodePtr = tagPtr->tagRootPtr;
    if (nodePtr == (Node *) NULL) {
	return NULL;
    }

    /*
     * Search from the root of the subtree that contains the tag down
     * to the level 0 node.
     */

    while (nodePtr->level > 0) {
	for (lastNodePtr = NULL, nodePtr = nodePtr->children.nodePtr ;
		nodePtr != (Node *) NULL; nodePtr = nodePtr->nextPtr) {
	    for (summaryPtr = nodePtr->summaryPtr ; summaryPtr != NULL;
		    summaryPtr = summaryPtr->nextPtr) {
		if (summaryPtr->tagPtr == tagPtr) {
		    lastNodePtr = nodePtr;
		    break;
		}
	    }
	}
	nodePtr = lastNodePtr;
    }

    /*
     * Work through the lines attached to the level-0 node.
     */
    last2SegPtr = NULL;
    lastoffset2 = 0;
    lastoffset = 0;
    for (lastLinePtr = NULL, linePtr = nodePtr->children.linePtr;
	    linePtr != (TkTextLine *) NULL; linePtr = linePtr->nextPtr) {
	for (offset = 0, lastSegPtr = NULL, segPtr = linePtr->segPtr ;
		segPtr != NULL; 
		offset += segPtr->size, segPtr = segPtr->nextPtr) {
	    if (((segPtr->typePtr == &tkTextToggleOnType)
		    || (segPtr->typePtr == &tkTextToggleOffType))
		    && (segPtr->body.toggle.tagPtr == tagPtr)) {
		lastSegPtr = segPtr;
		lastoffset = offset;
	    }
	}
	if (lastSegPtr != NULL) {
	    lastLinePtr = linePtr;
	    last2SegPtr = lastSegPtr;
	    lastoffset2 = lastoffset;
	}
    }
    indexPtr->tree = tree;
    indexPtr->linePtr = lastLinePtr;
    indexPtr->byteIndex = lastoffset2;
    return last2SegPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeStartSearch --
 *
 *	This procedure sets up a search for tag transitions involving
 *	a given tag (or all tags) in a given range of the text.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The information at *searchPtr is set up so that subsequent calls
 *	to TkBTreeNextTag or TkBTreePrevTag will return information about the
 *	locations of tag transitions.  Note that TkBTreeNextTag or 
 *	TkBTreePrevTag must be called to get the first transition.
 *	Note: unlike TkBTreeNextTag and TkBTreePrevTag, this routine does not
 *	guarantee that searchPtr->curIndex is equal to *index1Ptr.  It may be
 *	greater than that if *index1Ptr is less than the first tag transition.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeStartSearch(index1Ptr, index2Ptr, tagPtr, searchPtr)
    TkTextIndex *index1Ptr;		/* Search starts here.  Tag toggles
					 * at this position will not be
					 * returned. */
    TkTextIndex *index2Ptr;		/* Search stops here.  Tag toggles
					 * at this position *will* be
					 * returned. */
    TkTextTag *tagPtr;			/* Tag to search for.  NULL means
					 * search for any tag. */
    register TkTextSearch *searchPtr;	/* Where to store information about
					 * search's progress. */
{
    int offset;
    TkTextIndex index0;		/* First index of the tag */
    TkTextSegment *seg0Ptr;	/* First segment of the tag */

    /*
     * Find the segment that contains the first toggle for the tag.  This
     * may become the starting point in the search.
     */

    seg0Ptr = FindTagStart(index1Ptr->tree, tagPtr, &index0);
    if (seg0Ptr == (TkTextSegment *) NULL) {
	/*
	 * Even though there are no toggles, the display code still
	 * uses the search curIndex, so initialize that anyway.
	 */

	searchPtr->linesLeft = 0;
	searchPtr->curIndex = *index1Ptr;
	searchPtr->segPtr = NULL;
	searchPtr->nextPtr = NULL;
	return;
    }
    if (TkTextIndexCmp(index1Ptr, &index0) < 0) {
	/*
	 * Adjust start of search up to the first range of the tag
	 */

	searchPtr->curIndex = index0;
	searchPtr->segPtr = NULL;
	searchPtr->nextPtr = seg0Ptr;	/* Will be returned by NextTag */
	index1Ptr = &index0;
    } else {
	searchPtr->curIndex = *index1Ptr;
	searchPtr->segPtr = NULL;
	searchPtr->nextPtr = TkTextIndexToSeg(index1Ptr, &offset);
	searchPtr->curIndex.byteIndex -= offset;
    }
    searchPtr->lastPtr = TkTextIndexToSeg(index2Ptr, (int *) NULL);
    searchPtr->tagPtr = tagPtr;
    searchPtr->linesLeft = TkBTreeLineIndex(index2Ptr->linePtr) + 1
	    - TkBTreeLineIndex(index1Ptr->linePtr);
    searchPtr->allTags = (tagPtr == NULL);
    if (searchPtr->linesLeft == 1) {
	/*
	 * Starting and stopping segments are in the same line; mark the
	 * search as over immediately if the second segment is before the
	 * first.  A search does not return a toggle at the very start of
	 * the range, unless the range is artificially moved up to index0.
	 */
	if (((index1Ptr == &index0) && 
		(index1Ptr->byteIndex > index2Ptr->byteIndex)) ||
	    ((index1Ptr != &index0) && 
		(index1Ptr->byteIndex >= index2Ptr->byteIndex))) {
		searchPtr->linesLeft = 0;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeStartSearchBack --
 *
 *	This procedure sets up a search backwards for tag transitions involving
 *	a given tag (or all tags) in a given range of the text.  In the
 *	normal case the first index (*index1Ptr) is beyond the second
 *	index (*index2Ptr).
 *	
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The information at *searchPtr is set up so that subsequent calls
 *	to TkBTreePrevTag will return information about the
 *	locations of tag transitions.  Note that TkBTreePrevTag must be called
 *	to get the first transition.
 *	Note: unlike TkBTreeNextTag and TkBTreePrevTag, this routine does not
 *	guarantee that searchPtr->curIndex is equal to *index1Ptr.  It may be
 *	less than that if *index1Ptr is greater than the last tag transition.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeStartSearchBack(index1Ptr, index2Ptr, tagPtr, searchPtr)
    TkTextIndex *index1Ptr;		/* Search starts here.  Tag toggles
					 * at this position will not be
					 * returned. */
    TkTextIndex *index2Ptr;		/* Search stops here.  Tag toggles
					 * at this position *will* be
					 * returned. */
    TkTextTag *tagPtr;			/* Tag to search for.  NULL means
					 * search for any tag. */
    register TkTextSearch *searchPtr;	/* Where to store information about
					 * search's progress. */
{
    int offset;
    TkTextIndex index0;		/* Last index of the tag */
    TkTextIndex backOne;	/* One character before starting index */
    TkTextSegment *seg0Ptr;	/* Last segment of the tag */

    /*
     * Find the segment that contains the last toggle for the tag.  This
     * may become the starting point in the search.
     */

    seg0Ptr = FindTagEnd(index1Ptr->tree, tagPtr, &index0);
    if (seg0Ptr == (TkTextSegment *) NULL) {
	/*
	 * Even though there are no toggles, the display code still
	 * uses the search curIndex, so initialize that anyway.
	 */

	searchPtr->linesLeft = 0;
	searchPtr->curIndex = *index1Ptr;
	searchPtr->segPtr = NULL;
	searchPtr->nextPtr = NULL;
	return;
    }

    /*
     * Adjust the start of the search so it doesn't find any tag toggles
     * that are right at the index specified by the user.
     */

    if (TkTextIndexCmp(index1Ptr, &index0) > 0) {
	searchPtr->curIndex = index0;
	index1Ptr = &index0;
    } else {
	TkTextIndexBackChars(index1Ptr, 1, &searchPtr->curIndex);
    }
    searchPtr->segPtr = NULL;
    searchPtr->nextPtr = TkTextIndexToSeg(&searchPtr->curIndex, &offset);
    searchPtr->curIndex.byteIndex -= offset;

    /*
     * Adjust the end of the search so it does find toggles that are right
     * at the second index specified by the user.
     */

    if ((TkBTreeLineIndex(index2Ptr->linePtr) == 0) &&
	    (index2Ptr->byteIndex == 0)) {
	backOne = *index2Ptr;
	searchPtr->lastPtr = NULL;	/* Signals special case for 1.0 */
    } else {
	TkTextIndexBackChars(index2Ptr, 1, &backOne);
	searchPtr->lastPtr = TkTextIndexToSeg(&backOne, (int *) NULL);
    }
    searchPtr->tagPtr = tagPtr;
    searchPtr->linesLeft = TkBTreeLineIndex(index1Ptr->linePtr) + 1
	    - TkBTreeLineIndex(backOne.linePtr);
    searchPtr->allTags = (tagPtr == NULL);
    if (searchPtr->linesLeft == 1) {
	/*
	 * Starting and stopping segments are in the same line; mark the
	 * search as over immediately if the second segment is after the
	 * first.
	 */

	if (index1Ptr->byteIndex <= backOne.byteIndex) {
	    searchPtr->linesLeft = 0;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeNextTag --
 *
 *	Once a tag search has begun, successive calls to this procedure
 *	return successive tag toggles.  Note:  it is NOT SAFE to call this
 *	procedure if characters have been inserted into or deleted from
 *	the B-tree since the call to TkBTreeStartSearch.
 *
 * Results:
 *	The return value is 1 if another toggle was found that met the
 *	criteria specified in the call to TkBTreeStartSearch;  in this
 *	case searchPtr->curIndex gives the toggle's position and
 *	searchPtr->curTagPtr points to its segment.  0 is returned if
 *	no more matching tag transitions were found; in this case
 *	searchPtr->curIndex is the same as searchPtr->stopIndex.
 *
 * Side effects:
 *	Information in *searchPtr is modified to update the state of the
 *	search and indicate where the next tag toggle is located.
 *
 *----------------------------------------------------------------------
 */

int
TkBTreeNextTag(searchPtr)
    register TkTextSearch *searchPtr;	/* Information about search in
					 * progress;  must have been set up by
					 * call to TkBTreeStartSearch. */
{
    register TkTextSegment *segPtr;
    register Node *nodePtr;
    register Summary *summaryPtr;

    if (searchPtr->linesLeft <= 0) {
	goto searchOver;
    }

    /*
     * The outermost loop iterates over lines that may potentially contain
     * a relevant tag transition, starting from the current segment in
     * the current line.
     */

    segPtr = searchPtr->nextPtr;
    while (1) {
	/*
	 * Check for more tags on the current line.
	 */

	for ( ; segPtr != NULL; segPtr = segPtr->nextPtr) {
	    if (segPtr == searchPtr->lastPtr) {
		goto searchOver;
	    }
	    if (((segPtr->typePtr == &tkTextToggleOnType)
		    || (segPtr->typePtr == &tkTextToggleOffType))
		    && (searchPtr->allTags
		    || (segPtr->body.toggle.tagPtr == searchPtr->tagPtr))) {
		searchPtr->segPtr = segPtr;
		searchPtr->nextPtr = segPtr->nextPtr;
		searchPtr->tagPtr = segPtr->body.toggle.tagPtr;
		return 1;
	    }
	    searchPtr->curIndex.byteIndex += segPtr->size;
	}
    
	/*
	 * See if there are more lines associated with the current parent
	 * node.  If so, go back to the top of the loop to search the next
	 * one.
	 */

	nodePtr = searchPtr->curIndex.linePtr->parentPtr;
	searchPtr->curIndex.linePtr = searchPtr->curIndex.linePtr->nextPtr;
	searchPtr->linesLeft--;
	if (searchPtr->linesLeft <= 0) {
	    goto searchOver;
	}
	if (searchPtr->curIndex.linePtr != NULL) {
	    segPtr = searchPtr->curIndex.linePtr->segPtr;
	    searchPtr->curIndex.byteIndex = 0;
	    continue;
	}
	if (nodePtr == searchPtr->tagPtr->tagRootPtr) {
	    goto searchOver;
	}
    
	/*
	 * Search across and up through the B-tree's node hierarchy looking
	 * for the next node that has a relevant tag transition somewhere in
	 * its subtree.  Be sure to update linesLeft as we skip over large
	 * chunks of lines.
	 */
    
	while (1) {
	    while (nodePtr->nextPtr == NULL) {
		if (nodePtr->parentPtr == NULL ||
		    nodePtr->parentPtr == searchPtr->tagPtr->tagRootPtr) {
		    goto searchOver;
		}
		nodePtr = nodePtr->parentPtr;
	    }
	    nodePtr = nodePtr->nextPtr;
	    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
		    summaryPtr = summaryPtr->nextPtr) {
		if ((searchPtr->allTags) ||
			(summaryPtr->tagPtr == searchPtr->tagPtr)) {
		    goto gotNodeWithTag;
		}
	    }
	    searchPtr->linesLeft -= nodePtr->numLines;
	}
    
	/*
	 * At this point we've found a subtree that has a relevant tag
	 * transition.  Now search down (and across) through that subtree
	 * to find the first level-0 node that has a relevant tag transition.
	 */
    
	gotNodeWithTag:
	while (nodePtr->level > 0) {
	    for (nodePtr = nodePtr->children.nodePtr; ;
		    nodePtr = nodePtr->nextPtr) {
		for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
			summaryPtr = summaryPtr->nextPtr) {
		    if ((searchPtr->allTags)
			    || (summaryPtr->tagPtr == searchPtr->tagPtr)) {
			goto nextChild;
		    }
		}
		searchPtr->linesLeft -= nodePtr->numLines;
		if (nodePtr->nextPtr == NULL) {
		    panic("TkBTreeNextTag found incorrect tag summary info.");
		}
	    }
	    nextChild:
	    continue;
	}
    
	/*
	 * Now we're down to a level-0 node that contains a line that contains
	 * a relevant tag transition.  Set up line information and go back to
	 * the beginning of the loop to search through lines.
	 */

	searchPtr->curIndex.linePtr = nodePtr->children.linePtr;
	searchPtr->curIndex.byteIndex = 0;
	segPtr = searchPtr->curIndex.linePtr->segPtr;
	if (searchPtr->linesLeft <= 0) {
	    goto searchOver;
	}
	continue;
    }

    searchOver:
    searchPtr->linesLeft = 0;
    searchPtr->segPtr = NULL;
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreePrevTag --
 *
 *	Once a tag search has begun, successive calls to this procedure
 *	return successive tag toggles in the reverse direction.
 *	Note:  it is NOT SAFE to call this
 *	procedure if characters have been inserted into or deleted from
 *	the B-tree since the call to TkBTreeStartSearch.
 *
 * Results:
 *	The return value is 1 if another toggle was found that met the
 *	criteria specified in the call to TkBTreeStartSearch;  in this
 *	case searchPtr->curIndex gives the toggle's position and
 *	searchPtr->curTagPtr points to its segment.  0 is returned if
 *	no more matching tag transitions were found; in this case
 *	searchPtr->curIndex is the same as searchPtr->stopIndex.
 *
 * Side effects:
 *	Information in *searchPtr is modified to update the state of the
 *	search and indicate where the next tag toggle is located.
 *
 *----------------------------------------------------------------------
 */

int
TkBTreePrevTag(searchPtr)
    register TkTextSearch *searchPtr;	/* Information about search in
					 * progress;  must have been set up by
					 * call to TkBTreeStartSearch. */
{
    register TkTextSegment *segPtr, *prevPtr;
    register TkTextLine *linePtr, *prevLinePtr;
    register Node *nodePtr, *node2Ptr, *prevNodePtr;
    register Summary *summaryPtr;
    int byteIndex;
    int pastLast;			/* Saw last marker during scan */
    int linesSkipped;

    if (searchPtr->linesLeft <= 0) {
	goto searchOver;
    }

    /*
     * The outermost loop iterates over lines that may potentially contain
     * a relevant tag transition, starting from the current segment in
     * the current line.  "nextPtr" is maintained as the last segment in
     * a line that we can look at. 
     */

    while (1) {
	/*
	 * Check for the last toggle before the current segment on this line.
	 */
	byteIndex = 0;
	if (searchPtr->lastPtr == NULL) {
	    /* 
	     * Search back to the very beginning, so pastLast is irrelevent.
	     */
	    pastLast = 1; 
	} else {
	    pastLast = 0;
	}
	for (prevPtr = NULL, segPtr = searchPtr->curIndex.linePtr->segPtr ;
		segPtr != NULL && segPtr != searchPtr->nextPtr;
		segPtr = segPtr->nextPtr) {
	    if (((segPtr->typePtr == &tkTextToggleOnType)
		    || (segPtr->typePtr == &tkTextToggleOffType))
		    && (searchPtr->allTags
		    || (segPtr->body.toggle.tagPtr == searchPtr->tagPtr))) {
		prevPtr = segPtr;
		searchPtr->curIndex.byteIndex = byteIndex;
	    }
	    if (segPtr == searchPtr->lastPtr) {
	        prevPtr = NULL;   /* Segments earlier than last don't count */
		pastLast = 1;
	    }
	    byteIndex += segPtr->size;
	}
	if (prevPtr != NULL) {
	    if (searchPtr->linesLeft == 1 && !pastLast) {
		/*
		 * We found a segment that is before the stopping index.
		 * Note that it is OK if prevPtr == lastPtr.
		 */
		goto searchOver;
	    }
	    searchPtr->segPtr = prevPtr;
	    searchPtr->nextPtr = prevPtr;
	    searchPtr->tagPtr = prevPtr->body.toggle.tagPtr;
	    return 1;
	}
    
	searchPtr->linesLeft--;
	if (searchPtr->linesLeft <= 0) {
	    goto searchOver;
	}

	/*
	 * See if there are more lines associated with the current parent
	 * node.  If so, go back to the top of the loop to search the previous
	 * one.
	 */

	nodePtr = searchPtr->curIndex.linePtr->parentPtr;
	for (prevLinePtr = NULL, linePtr = nodePtr->children.linePtr;
		linePtr != NULL && linePtr != searchPtr->curIndex.linePtr;
		prevLinePtr = linePtr, linePtr = linePtr->nextPtr) {
	    /* empty loop body */ ;
	}
	if (prevLinePtr != NULL) {
	    searchPtr->curIndex.linePtr = prevLinePtr;
	    searchPtr->nextPtr = NULL;
	    continue;
	}
	if (nodePtr == searchPtr->tagPtr->tagRootPtr) {
	    goto searchOver;
	}
    
	/*
	 * Search across and up through the B-tree's node hierarchy looking
	 * for the previous node that has a relevant tag transition somewhere in
	 * its subtree.  The search and line counting is trickier with/out
	 * back pointers. We'll scan all the nodes under a parent up to
	 * the current node, searching all of them for tag state.  The last
	 * one we find, if any, is recorded in prevNodePtr, and any nodes
	 * past prevNodePtr that don't have tag state increment linesSkipped.
	 */
    
	while (1) {
	    for (prevNodePtr = NULL, linesSkipped = 0,
		    node2Ptr = nodePtr->parentPtr->children.nodePtr ;
		    node2Ptr != nodePtr;  node2Ptr = node2Ptr->nextPtr) {
		for (summaryPtr = node2Ptr->summaryPtr; summaryPtr != NULL;
			summaryPtr = summaryPtr->nextPtr) {
		    if ((searchPtr->allTags) ||
			    (summaryPtr->tagPtr == searchPtr->tagPtr)) {
			prevNodePtr = node2Ptr;
			linesSkipped = 0;
			goto keepLooking;
		    }
		}
		linesSkipped += node2Ptr->numLines;

		keepLooking:
		continue;
	    }
	    if (prevNodePtr != NULL) {
		nodePtr = prevNodePtr;
		searchPtr->linesLeft -= linesSkipped;
		goto gotNodeWithTag;
	    }
	    nodePtr = nodePtr->parentPtr;
	    if (nodePtr->parentPtr == NULL ||
		nodePtr == searchPtr->tagPtr->tagRootPtr) {
		goto searchOver;
	    }
	}
    
	/*
	 * At this point we've found a subtree that has a relevant tag
	 * transition.  Now search down (and across) through that subtree
	 * to find the last level-0 node that has a relevant tag transition.
	 */
    
	gotNodeWithTag:
	while (nodePtr->level > 0) {
	    for (linesSkipped = 0, prevNodePtr = NULL,
		    nodePtr = nodePtr->children.nodePtr; nodePtr != NULL ;
		    nodePtr = nodePtr->nextPtr) {
		for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
			summaryPtr = summaryPtr->nextPtr) {
		    if ((searchPtr->allTags)
			    || (summaryPtr->tagPtr == searchPtr->tagPtr)) {
			prevNodePtr = nodePtr;
			linesSkipped = 0;
			goto keepLooking2;
		    }
		}
		linesSkipped += nodePtr->numLines;

		keepLooking2:
		continue;
	    }
	    if (prevNodePtr == NULL) {
		panic("TkBTreePrevTag found incorrect tag summary info.");
	    }
	    searchPtr->linesLeft -= linesSkipped;
	    nodePtr = prevNodePtr;
	}
    
	/*
	 * Now we're down to a level-0 node that contains a line that contains
	 * a relevant tag transition.  Set up line information and go back to
	 * the beginning of the loop to search through lines.  We start with
	 * the last line below the node.
	 */

	for (prevLinePtr = NULL, linePtr = nodePtr->children.linePtr;
		linePtr != NULL ;
		prevLinePtr = linePtr, linePtr = linePtr->nextPtr) {
	    /* empty loop body */ ;
	}
	searchPtr->curIndex.linePtr = prevLinePtr;
	searchPtr->curIndex.byteIndex = 0;
	if (searchPtr->linesLeft <= 0) {
	    goto searchOver;
	}
	continue;
    }

    searchOver:
    searchPtr->linesLeft = 0;
    searchPtr->segPtr = NULL;
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeCharTagged --
 *
 *	Determine whether a particular character has a particular tag.
 *
 * Results:
 *	The return value is 1 if the given tag is in effect at the
 *	character given by linePtr and ch, and 0 otherwise.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
TkBTreeCharTagged(indexPtr, tagPtr)
    TkTextIndex *indexPtr;		/* Indicates a character position at
					 * which to check for a tag. */
    TkTextTag *tagPtr;			/* Tag of interest. */
{
    register Node *nodePtr;
    register TkTextLine *siblingLinePtr;
    register TkTextSegment *segPtr;
    TkTextSegment *toggleSegPtr;
    int toggles, index;

    /* 
     * Check for toggles for the tag in indexPtr's line but before
     * indexPtr.  If there is one, its type indicates whether or
     * not the character is tagged.
     */

    toggleSegPtr = NULL;
    for (index = 0, segPtr = indexPtr->linePtr->segPtr;
	    (index + segPtr->size) <= indexPtr->byteIndex;
	    index += segPtr->size, segPtr = segPtr->nextPtr) {
	if (((segPtr->typePtr == &tkTextToggleOnType)
		|| (segPtr->typePtr == &tkTextToggleOffType))
		&& (segPtr->body.toggle.tagPtr == tagPtr)) {
	    toggleSegPtr = segPtr;
	}
    }
    if (toggleSegPtr != NULL) {
	return (toggleSegPtr->typePtr == &tkTextToggleOnType);
    }

    /*
     * No toggle in this line.  Look for toggles for the tag in lines
     * that are predecessors of indexPtr->linePtr but under the same
     * level-0 node.
     */

    for (siblingLinePtr = indexPtr->linePtr->parentPtr->children.linePtr;
	    siblingLinePtr != indexPtr->linePtr;
	    siblingLinePtr = siblingLinePtr->nextPtr) {
	for (segPtr = siblingLinePtr->segPtr; segPtr != NULL;
		segPtr = segPtr->nextPtr) {
	    if (((segPtr->typePtr == &tkTextToggleOnType)
		    || (segPtr->typePtr == &tkTextToggleOffType))
		    && (segPtr->body.toggle.tagPtr == tagPtr)) {
		toggleSegPtr = segPtr;
	    }
	}
    }
    if (toggleSegPtr != NULL) {
	return (toggleSegPtr->typePtr == &tkTextToggleOnType);
    }

    /*
     * No toggle in this node.  Scan upwards through the ancestors of
     * this node, counting the number of toggles of the given tag in
     * siblings that precede that node.
     */

    toggles = 0;
    for (nodePtr = indexPtr->linePtr->parentPtr; nodePtr->parentPtr != NULL;
	    nodePtr = nodePtr->parentPtr) {
	register Node *siblingPtr;
	register Summary *summaryPtr;

	for (siblingPtr = nodePtr->parentPtr->children.nodePtr; 
		siblingPtr != nodePtr; siblingPtr = siblingPtr->nextPtr) {
	    for (summaryPtr = siblingPtr->summaryPtr; summaryPtr != NULL;
		    summaryPtr = summaryPtr->nextPtr) {
		if (summaryPtr->tagPtr == tagPtr) {
		    toggles += summaryPtr->toggleCount;
		}
	    }
	}
	if (nodePtr == tagPtr->tagRootPtr) {
	    break;
	}
    }

    /*
     * An odd number of toggles means that the tag is present at the
     * given point.
     */

    return toggles & 1;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeGetTags --
 *
 *	Return information about all of the tags that are associated
 *	with a particular character in a B-tree of text.
 *
 * Results:
 *	The return value is a malloc-ed array containing pointers to
 *	information for each of the tags that is associated with
 *	the character at the position given by linePtr and ch.  The
 *	word at *numTagsPtr is filled in with the number of pointers
 *	in the array.  It is up to the caller to free the array by
 *	passing it to free.  If there are no tags at the given character
 *	then a NULL pointer is returned and *numTagsPtr will be set to 0.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
TkTextTag **
TkBTreeGetTags(indexPtr, numTagsPtr)
    TkTextIndex *indexPtr;	/* Indicates a particular position in
				 * the B-tree. */
    int *numTagsPtr;		/* Store number of tags found at this
				 * location. */
{
    register Node *nodePtr;
    register TkTextLine *siblingLinePtr;
    register TkTextSegment *segPtr;
    int src, dst, index;
    TagInfo tagInfo;
#define NUM_TAG_INFOS 10

    tagInfo.numTags = 0;
    tagInfo.arraySize = NUM_TAG_INFOS;
    tagInfo.tagPtrs = (TkTextTag **) ckalloc((unsigned)
	    NUM_TAG_INFOS*sizeof(TkTextTag *));
    tagInfo.counts = (int *) ckalloc((unsigned)
	    NUM_TAG_INFOS*sizeof(int));

    /*
     * Record tag toggles within the line of indexPtr but preceding
     * indexPtr.
     */

    for (index = 0, segPtr = indexPtr->linePtr->segPtr;
	    (index + segPtr->size) <= indexPtr->byteIndex;
	    index += segPtr->size, segPtr = segPtr->nextPtr) {
	if ((segPtr->typePtr == &tkTextToggleOnType)
		|| (segPtr->typePtr == &tkTextToggleOffType)) {
	    IncCount(segPtr->body.toggle.tagPtr, 1, &tagInfo);
	}
    }

    /*
     * Record toggles for tags in lines that are predecessors of
     * indexPtr->linePtr but under the same level-0 node.
     */

    for (siblingLinePtr = indexPtr->linePtr->parentPtr->children.linePtr;
	    siblingLinePtr != indexPtr->linePtr;
	    siblingLinePtr = siblingLinePtr->nextPtr) {
	for (segPtr = siblingLinePtr->segPtr; segPtr != NULL;
		segPtr = segPtr->nextPtr) {
	    if ((segPtr->typePtr == &tkTextToggleOnType)
		    || (segPtr->typePtr == &tkTextToggleOffType)) {
		IncCount(segPtr->body.toggle.tagPtr, 1, &tagInfo);
	    }
	}
    }

    /*
     * For each node in the ancestry of this line, record tag toggles
     * for all siblings that precede that node.
     */

    for (nodePtr = indexPtr->linePtr->parentPtr; nodePtr->parentPtr != NULL;
	    nodePtr = nodePtr->parentPtr) {
	register Node *siblingPtr;
	register Summary *summaryPtr;

	for (siblingPtr = nodePtr->parentPtr->children.nodePtr; 
		siblingPtr != nodePtr; siblingPtr = siblingPtr->nextPtr) {
	    for (summaryPtr = siblingPtr->summaryPtr; summaryPtr != NULL;
		    summaryPtr = summaryPtr->nextPtr) {
		if (summaryPtr->toggleCount & 1) {
		    IncCount(summaryPtr->tagPtr, summaryPtr->toggleCount,
			    &tagInfo);
		}
	    }
	}
    }

    /*
     * Go through the tag information and squash out all of the tags
     * that have even toggle counts (these tags exist before the point
     * of interest, but not at the desired character itself).
     */

    for (src = 0, dst = 0; src < tagInfo.numTags; src++) {
	if (tagInfo.counts[src] & 1) {
	    tagInfo.tagPtrs[dst] = tagInfo.tagPtrs[src];
	    dst++;
	}
    }
    *numTagsPtr = dst;
    ckfree((char *) tagInfo.counts);
    if (dst == 0) {
	ckfree((char *) tagInfo.tagPtrs);
	return NULL;
    }
    return tagInfo.tagPtrs;
}


/*
   special case to just return information about elided attribute
   specialized from TkBTreeGetTags(indexPtr, numTagsPtr) and GetStyle(textPtr, indexPtr)
   just need to keep track of invisibility settings for each priority, pick highest one active at end
*/
int
TkTextIsElided(textPtr, indexPtr)
    TkText *textPtr;		/* Overall information about text widget. */
    TkTextIndex *indexPtr;	/* The character in the text for which
				 * display information is wanted. */
{
#define LOTSA_TAGS 1000
	int elide = 0;		/* if nobody says otherwise, it's visible */

	int deftagCnts[LOTSA_TAGS];
	int *tagCnts = deftagCnts;
	TkTextTag *deftagPtrs[LOTSA_TAGS];
	TkTextTag **tagPtrs = deftagPtrs;
	int numTags = textPtr->numTags;
    register Node *nodePtr;
    register TkTextLine *siblingLinePtr;
    register TkTextSegment *segPtr;
    register TkTextTag *tagPtr;
    register int i, index;

	/* almost always avoid malloc, so stay out of system calls */
	if (LOTSA_TAGS < numTags) {
	    tagCnts = (int *)ckalloc((unsigned)sizeof(int) * numTags);
	    tagPtrs = (TkTextTag **)ckalloc((unsigned)sizeof(TkTextTag *) * numTags);
	}
 
	for (i=0; i<numTags; i++) tagCnts[i]=0;


    /*
     * Record tag toggles within the line of indexPtr but preceding
     * indexPtr.
     */

    for (index = 0, segPtr = indexPtr->linePtr->segPtr;
	    (index + segPtr->size) <= indexPtr->byteIndex;
	    index += segPtr->size, segPtr = segPtr->nextPtr) {
	if ((segPtr->typePtr == &tkTextToggleOnType)
	    || (segPtr->typePtr == &tkTextToggleOffType)) {
	    tagPtr = segPtr->body.toggle.tagPtr;
	    if (tagPtr->state != TK_STATE_NULL) {
		   tagPtrs[tagPtr->priority] = tagPtr;
		   tagCnts[tagPtr->priority]++;
	    }
	}
    }

    /*
     * Record toggles for tags in lines that are predecessors of
     * indexPtr->linePtr but under the same level-0 node.
     */

    for (siblingLinePtr = indexPtr->linePtr->parentPtr->children.linePtr;
	    siblingLinePtr != indexPtr->linePtr;
	    siblingLinePtr = siblingLinePtr->nextPtr) {
	for (segPtr = siblingLinePtr->segPtr; segPtr != NULL;
		segPtr = segPtr->nextPtr) {
	    if ((segPtr->typePtr == &tkTextToggleOnType)
		   || (segPtr->typePtr == &tkTextToggleOffType)) {
		   tagPtr = segPtr->body.toggle.tagPtr;
		   if (tagPtr->state != TK_STATE_NULL) {
			  tagPtrs[tagPtr->priority] = tagPtr;
			  tagCnts[tagPtr->priority]++;
		   }
	    }
	}
    }

    /*
     * For each node in the ancestry of this line, record tag toggles
     * for all siblings that precede that node.
     */

    for (nodePtr = indexPtr->linePtr->parentPtr; nodePtr->parentPtr != NULL;
	    nodePtr = nodePtr->parentPtr) {
	register Node *siblingPtr;
	register Summary *summaryPtr;

	for (siblingPtr = nodePtr->parentPtr->children.nodePtr; 
		siblingPtr != nodePtr; siblingPtr = siblingPtr->nextPtr) {
	    for (summaryPtr = siblingPtr->summaryPtr; summaryPtr != NULL;
		    summaryPtr = summaryPtr->nextPtr) {
		if (summaryPtr->toggleCount & 1) {
		    tagPtr = summaryPtr->tagPtr;
		    if (tagPtr->state != TK_STATE_NULL) {
			   tagPtrs[tagPtr->priority] = tagPtr;
			   tagCnts[tagPtr->priority] += summaryPtr->toggleCount;
		    }
		}
	    }
	}
    }


    /*
     * Now traverse from highest priority to lowest, 
     * take elided value from first odd count (= on)
     */

    for (i = numTags-1; i >=0; i--) {
	   if (tagCnts[i] & 1) {
#ifndef ALWAYS_SHOW_SELECTION
		  /* who would make the selection elided? */
		  if ((tagPtr == textPtr->selTagPtr) && !(textPtr->flags & GOT_FOCUS)) {
			 continue;
		  }
#endif
		  elide = (tagPtrs[i]->state == TK_STATE_HIDDEN);
		  break;
	   }
    }

    if (LOTSA_TAGS < numTags) {
	   ckfree((char *) tagCnts);
	   ckfree((char *) tagPtrs);
    }

    return elide;
}

/*
 *----------------------------------------------------------------------
 *
 * IncCount --
 *
 *	This is a utility procedure used by TkBTreeGetTags.  It
 *	increments the count for a particular tag, adding a new
 *	entry for that tag if there wasn't one previously.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The information at *tagInfoPtr may be modified, and the arrays
 *	may be reallocated to make them larger.
 *
 *----------------------------------------------------------------------
 */

static void
IncCount(tagPtr, inc, tagInfoPtr)
    TkTextTag *tagPtr;		/* Handle for tag. */
    int inc;			/* Amount by which to increment tag count. */
    TagInfo *tagInfoPtr;	/* Holds cumulative information about tags;
				 * increment count here. */
{
    register TkTextTag **tagPtrPtr;
    int count;

    for (tagPtrPtr = tagInfoPtr->tagPtrs, count = tagInfoPtr->numTags;
	    count > 0; tagPtrPtr++, count--) {
	if (*tagPtrPtr == tagPtr) {
	    tagInfoPtr->counts[tagInfoPtr->numTags-count] += inc;
	    return;
	}
    }

    /*
     * There isn't currently an entry for this tag, so we have to
     * make a new one.  If the arrays are full, then enlarge the
     * arrays first.
     */

    if (tagInfoPtr->numTags == tagInfoPtr->arraySize) {
	TkTextTag **newTags;
	int *newCounts, newSize;

	newSize = 2*tagInfoPtr->arraySize;
	newTags = (TkTextTag **) ckalloc((unsigned)
		(newSize*sizeof(TkTextTag *)));
	memcpy((VOID *) newTags, (VOID *) tagInfoPtr->tagPtrs,
		tagInfoPtr->arraySize * sizeof(TkTextTag *));
	ckfree((char *) tagInfoPtr->tagPtrs);
	tagInfoPtr->tagPtrs = newTags;
	newCounts = (int *) ckalloc((unsigned) (newSize*sizeof(int)));
	memcpy((VOID *) newCounts, (VOID *) tagInfoPtr->counts,
		tagInfoPtr->arraySize * sizeof(int));
	ckfree((char *) tagInfoPtr->counts);
	tagInfoPtr->counts = newCounts;
	tagInfoPtr->arraySize = newSize;
    }

    tagInfoPtr->tagPtrs[tagInfoPtr->numTags] = tagPtr;
    tagInfoPtr->counts[tagInfoPtr->numTags] = inc;
    tagInfoPtr->numTags++;
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeCheck --
 *
 *	This procedure runs a set of consistency checks over a B-tree
 *	and panics if any inconsistencies are found.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If a structural defect is found, the procedure panics with an
 *	error message.
 *
 *----------------------------------------------------------------------
 */

void
TkBTreeCheck(tree)
    TkTextBTree tree;		/* Tree to check. */
{
    BTree *treePtr = (BTree *) tree;
    register Summary *summaryPtr;
    register Node *nodePtr;
    register TkTextLine *linePtr;
    register TkTextSegment *segPtr;
    register TkTextTag *tagPtr;
    Tcl_HashEntry *entryPtr;
    Tcl_HashSearch search;
    int count;

    /*
     * Make sure that the tag toggle counts and the tag root pointers are OK.
     */
    for (entryPtr = Tcl_FirstHashEntry(&treePtr->textPtr->tagTable, &search);
	    entryPtr != NULL ; entryPtr = Tcl_NextHashEntry(&search)) {
	tagPtr = (TkTextTag *) Tcl_GetHashValue(entryPtr);
	nodePtr = tagPtr->tagRootPtr;
	if (nodePtr == (Node *) NULL) {
	    if (tagPtr->toggleCount != 0) {
		panic("TkBTreeCheck found \"%s\" with toggles (%d) but no root",
		    tagPtr->name, tagPtr->toggleCount);
	    }
	    continue;		/* no ranges for the tag */
	} else if (tagPtr->toggleCount == 0) {
	    panic("TkBTreeCheck found root for \"%s\" with no toggles",
		    tagPtr->name);
	} else if (tagPtr->toggleCount & 1) {
	    panic("TkBTreeCheck found odd toggle count for \"%s\" (%d)",
		    tagPtr->name, tagPtr->toggleCount);
	}
	for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
		summaryPtr = summaryPtr->nextPtr) {
	    if (summaryPtr->tagPtr == tagPtr) {
		panic("TkBTreeCheck found root node with summary info");
	    }
	}
	count = 0;
	if (nodePtr->level > 0) {
	    for (nodePtr = nodePtr->children.nodePtr ; nodePtr != NULL ;
		    nodePtr = nodePtr->nextPtr) {
		for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
			summaryPtr = summaryPtr->nextPtr) {
		    if (summaryPtr->tagPtr == tagPtr) {
			count += summaryPtr->toggleCount;
		    }
		}
	    }
	} else {
	    for (linePtr = nodePtr->children.linePtr ; linePtr != NULL ;
		    linePtr = linePtr->nextPtr) {
		for (segPtr = linePtr->segPtr; segPtr != NULL;
			segPtr = segPtr->nextPtr) {
		    if ((segPtr->typePtr == &tkTextToggleOnType ||
			 segPtr->typePtr == &tkTextToggleOffType) &&
			 segPtr->body.toggle.tagPtr == tagPtr) {
			count++;
		    }
		}
	    }
	}
	if (count != tagPtr->toggleCount) {
	    panic("TkBTreeCheck toggleCount (%d) wrong for \"%s\" should be (%d)",
		tagPtr->toggleCount, tagPtr->name, count);
	}
    }

    /*
     * Call a recursive procedure to do the main body of checks.
     */

    nodePtr = treePtr->rootPtr;
    CheckNodeConsistency(treePtr->rootPtr);

    /*
     * Make sure that there are at least two lines in the text and
     * that the last line has no characters except a newline.
     */

    if (nodePtr->numLines < 2) {
	panic("TkBTreeCheck: less than 2 lines in tree");
    }
    while (nodePtr->level > 0) {
	nodePtr = nodePtr->children.nodePtr;
	while (nodePtr->nextPtr != NULL) {
	    nodePtr = nodePtr->nextPtr;
	}
    }
    linePtr = nodePtr->children.linePtr;
    while (linePtr->nextPtr != NULL) {
	linePtr = linePtr->nextPtr;
    }
    segPtr = linePtr->segPtr;
    while ((segPtr->typePtr == &tkTextToggleOffType)
	    || (segPtr->typePtr == &tkTextRightMarkType)
	    || (segPtr->typePtr == &tkTextLeftMarkType)) {
	/*
	 * It's OK to toggle a tag off in the last line, but
	 * not to start a new range.  It's also OK to have marks
	 * in the last line.
	 */

	segPtr = segPtr->nextPtr;
    }
    if (segPtr->typePtr != &tkTextCharType) {
	panic("TkBTreeCheck: last line has bogus segment type");
    }
    if (segPtr->nextPtr != NULL) {
	panic("TkBTreeCheck: last line has too many segments");
    }
    if (segPtr->size != 1) {
	panic("TkBTreeCheck: last line has wrong # characters: %d",
		segPtr->size);
    }
    if ((segPtr->body.chars[0] != '\n') || (segPtr->body.chars[1] != 0)) {
	panic("TkBTreeCheck: last line had bad value: %s",
		segPtr->body.chars);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * CheckNodeConsistency --
 *
 *	This procedure is called as part of consistency checking for
 *	B-trees:  it checks several aspects of a node and also runs
 *	checks recursively on the node's children.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If anything suspicious is found in the tree structure, the
 *	procedure panics.
 *
 *----------------------------------------------------------------------
 */

static void
CheckNodeConsistency(nodePtr)
    register Node *nodePtr;		/* Node whose subtree should be
					 * checked. */
{
    register Node *childNodePtr;
    register Summary *summaryPtr, *summaryPtr2;
    register TkTextLine *linePtr;
    register TkTextSegment *segPtr;
    int numChildren, numLines, toggleCount, minChildren;

    if (nodePtr->parentPtr != NULL) {
	minChildren = MIN_CHILDREN;
    } else if (nodePtr->level > 0) {
	minChildren = 2;
    } else  {
	minChildren = 1;
    }
    if ((nodePtr->numChildren < minChildren)
	    || (nodePtr->numChildren > MAX_CHILDREN)) {
	panic("CheckNodeConsistency: bad child count (%d)",
		nodePtr->numChildren);
    }

    numChildren = 0;
    numLines = 0;
    if (nodePtr->level == 0) {
	for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
		linePtr = linePtr->nextPtr) {
	    if (linePtr->parentPtr != nodePtr) {
		panic("CheckNodeConsistency: line doesn't point to parent");
	    }
	    if (linePtr->segPtr == NULL) {
		panic("CheckNodeConsistency: line has no segments");
	    }
	    for (segPtr = linePtr->segPtr; segPtr != NULL;
		    segPtr = segPtr->nextPtr) {
		if (segPtr->typePtr->checkProc != NULL) {
		    (*segPtr->typePtr->checkProc)(segPtr, linePtr);
		}
		if ((segPtr->size == 0) && (!segPtr->typePtr->leftGravity)
			&& (segPtr->nextPtr != NULL)
			&& (segPtr->nextPtr->size == 0)
			&& (segPtr->nextPtr->typePtr->leftGravity)) {
		    panic("CheckNodeConsistency: wrong segment order for gravity");
		}
		if ((segPtr->nextPtr == NULL)
			&& (segPtr->typePtr != &tkTextCharType)) {
		    panic("CheckNodeConsistency: line ended with wrong type");
		}
	    }
	    numChildren++;
	    numLines++;
	}
    } else {
	for (childNodePtr = nodePtr->children.nodePtr; childNodePtr != NULL;
		childNodePtr = childNodePtr->nextPtr) {
	    if (childNodePtr->parentPtr != nodePtr) {
		panic("CheckNodeConsistency: node doesn't point to parent");
	    }
	    if (childNodePtr->level != (nodePtr->level-1)) {
		panic("CheckNodeConsistency: level mismatch (%d %d)",
			nodePtr->level, childNodePtr->level);
	    }
	    CheckNodeConsistency(childNodePtr);
	    for (summaryPtr = childNodePtr->summaryPtr; summaryPtr != NULL;
			summaryPtr = summaryPtr->nextPtr) {
		for (summaryPtr2 = nodePtr->summaryPtr; ;
			summaryPtr2 = summaryPtr2->nextPtr) {
		    if (summaryPtr2 == NULL) {
			if (summaryPtr->tagPtr->tagRootPtr == nodePtr) {
			    break;
			}
			panic("CheckNodeConsistency: node tag \"%s\" not %s",
				summaryPtr->tagPtr->name,
				"present in parent summaries");
		    }
		    if (summaryPtr->tagPtr == summaryPtr2->tagPtr) {
			break;
		    }
		}
	    }
	    numChildren++;
	    numLines += childNodePtr->numLines;
	}
    }
    if (numChildren != nodePtr->numChildren) {
	panic("CheckNodeConsistency: mismatch in numChildren (%d %d)",
		numChildren, nodePtr->numChildren);
    }
    if (numLines != nodePtr->numLines) {
	panic("CheckNodeConsistency: mismatch in numLines (%d %d)",
		numLines, nodePtr->numLines);
    }

    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
	    summaryPtr = summaryPtr->nextPtr) {
	if (summaryPtr->tagPtr->toggleCount == summaryPtr->toggleCount) {
	    panic("CheckNodeConsistency: found unpruned root for \"%s\"",
		summaryPtr->tagPtr->name);
	}
	toggleCount = 0;
	if (nodePtr->level == 0) {
	    for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
		    linePtr = linePtr->nextPtr) {
		for (segPtr = linePtr->segPtr; segPtr != NULL;
			segPtr = segPtr->nextPtr) {
		    if ((segPtr->typePtr != &tkTextToggleOnType)
			    && (segPtr->typePtr != &tkTextToggleOffType)) {
			continue;
		    }
		    if (segPtr->body.toggle.tagPtr == summaryPtr->tagPtr) {
			toggleCount ++;
		    }
		}
	    }
	} else {
	    for (childNodePtr = nodePtr->children.nodePtr;
		    childNodePtr != NULL;
		    childNodePtr = childNodePtr->nextPtr) {
		for (summaryPtr2 = childNodePtr->summaryPtr;
			summaryPtr2 != NULL;
			summaryPtr2 = summaryPtr2->nextPtr) {
		    if (summaryPtr2->tagPtr == summaryPtr->tagPtr) {
			toggleCount += summaryPtr2->toggleCount;
		    }
		}
	    }
	}
	if (toggleCount != summaryPtr->toggleCount) {
	    panic("CheckNodeConsistency: mismatch in toggleCount (%d %d)",
		    toggleCount, summaryPtr->toggleCount);
	}
	for (summaryPtr2 = summaryPtr->nextPtr; summaryPtr2 != NULL;
		summaryPtr2 = summaryPtr2->nextPtr) {
	    if (summaryPtr2->tagPtr == summaryPtr->tagPtr) {
		panic("CheckNodeConsistency: duplicated node tag: %s",
			summaryPtr->tagPtr->name);
	    }
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Rebalance --
 *
 *	This procedure is called when a node of a B-tree appears to be
 *	out of balance (too many children, or too few).  It rebalances
 *	that node and all of its ancestors in the tree.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The internal structure of treePtr may change.
 *
 *----------------------------------------------------------------------
 */

static void
Rebalance(treePtr, nodePtr)
    BTree *treePtr;			/* Tree that is being rebalanced. */
    register Node *nodePtr;		/* Node that may be out of balance. */
{
    /*
     * Loop over the entire ancestral chain of the node, working up
     * through the tree one node at a time until the root node has
     * been processed.
     */

    for ( ; nodePtr != NULL; nodePtr = nodePtr->parentPtr) {
	register Node *newPtr, *childPtr;
	register TkTextLine *linePtr;
	int i;

	/*
	 * Check to see if the node has too many children.  If it does,
	 * then split off all but the first MIN_CHILDREN into a separate
	 * node following the original one.  Then repeat until the
	 * node has a decent size.
	 */

	if (nodePtr->numChildren > MAX_CHILDREN) {
	    while (1) {
		/*
		 * If the node being split is the root node, then make a
		 * new root node above it first.
		 */
    
		if (nodePtr->parentPtr == NULL) {
		    newPtr = (Node *) ckalloc(sizeof(Node));
		    newPtr->parentPtr = NULL;
		    newPtr->nextPtr = NULL;
		    newPtr->summaryPtr = NULL;
		    newPtr->level = nodePtr->level + 1;
		    newPtr->children.nodePtr = nodePtr;
		    newPtr->numChildren = 1;
		    newPtr->numLines = nodePtr->numLines;
		    RecomputeNodeCounts(newPtr);
		    treePtr->rootPtr = newPtr;
		}
		newPtr = (Node *) ckalloc(sizeof(Node));
		newPtr->parentPtr = nodePtr->parentPtr;
		newPtr->nextPtr = nodePtr->nextPtr;
		nodePtr->nextPtr = newPtr;
		newPtr->summaryPtr = NULL;
		newPtr->level = nodePtr->level;
		newPtr->numChildren = nodePtr->numChildren - MIN_CHILDREN;
		if (nodePtr->level == 0) {
		    for (i = MIN_CHILDREN-1,
			    linePtr = nodePtr->children.linePtr;
			    i > 0; i--, linePtr = linePtr->nextPtr) {
			/* Empty loop body. */
		    }
		    newPtr->children.linePtr = linePtr->nextPtr;
		    linePtr->nextPtr = NULL;
		} else {
		    for (i = MIN_CHILDREN-1,
			    childPtr = nodePtr->children.nodePtr;
			    i > 0; i--, childPtr = childPtr->nextPtr) {
			/* Empty loop body. */
		    }
		    newPtr->children.nodePtr = childPtr->nextPtr;
		    childPtr->nextPtr = NULL;
		}
		RecomputeNodeCounts(nodePtr);
		nodePtr->parentPtr->numChildren++;
		nodePtr = newPtr;
		if (nodePtr->numChildren <= MAX_CHILDREN) {
		    RecomputeNodeCounts(nodePtr);
		    break;
		}
	    }
	}

	while (nodePtr->numChildren < MIN_CHILDREN) {
	    register Node *otherPtr;
	    Node *halfwayNodePtr = NULL;	/* Initialization needed only */
	    TkTextLine *halfwayLinePtr = NULL;	/* to prevent cc warnings. */
	    int totalChildren, firstChildren, i;

	    /*
	     * Too few children for this node.  If this is the root then,
	     * it's OK for it to have less than MIN_CHILDREN children
	     * as long as it's got at least two.  If it has only one
	     * (and isn't at level 0), then chop the root node out of
	     * the tree and use its child as the new root.
	     */

	    if (nodePtr->parentPtr == NULL) {
		if ((nodePtr->numChildren == 1) && (nodePtr->level > 0)) {
		    treePtr->rootPtr = nodePtr->children.nodePtr;
		    treePtr->rootPtr->parentPtr = NULL;
		    DeleteSummaries(nodePtr->summaryPtr);
		    ckfree((char *) nodePtr);
		}
		return;
	    }

	    /*
	     * Not the root.  Make sure that there are siblings to
	     * balance with.
	     */

	    if (nodePtr->parentPtr->numChildren < 2) {
		Rebalance(treePtr, nodePtr->parentPtr);
		continue;
	    }

	    /*
	     * Find a sibling neighbor to borrow from, and arrange for
	     * nodePtr to be the earlier of the pair.
	     */

	    if (nodePtr->nextPtr == NULL) {
		for (otherPtr = nodePtr->parentPtr->children.nodePtr;
			otherPtr->nextPtr != nodePtr;
			otherPtr = otherPtr->nextPtr) {
		    /* Empty loop body. */
		}
		nodePtr = otherPtr;
	    }
	    otherPtr = nodePtr->nextPtr;

	    /*
	     * We're going to either merge the two siblings together
	     * into one node or redivide the children among them to
	     * balance their loads.  As preparation, join their two
	     * child lists into a single list and remember the half-way
	     * point in the list.
	     */

	    totalChildren = nodePtr->numChildren + otherPtr->numChildren;
	    firstChildren = totalChildren/2;
	    if (nodePtr->children.nodePtr == NULL) {
		nodePtr->children = otherPtr->children;
		otherPtr->children.nodePtr = NULL;
		otherPtr->children.linePtr = NULL;
	    }
	    if (nodePtr->level == 0) {
		register TkTextLine *linePtr;

		for (linePtr = nodePtr->children.linePtr, i = 1;
			linePtr->nextPtr != NULL;
			linePtr = linePtr->nextPtr, i++) {
		    if (i == firstChildren) {
			halfwayLinePtr = linePtr;
		    }
		}
		linePtr->nextPtr = otherPtr->children.linePtr;
		while (i <= firstChildren) {
		    halfwayLinePtr = linePtr;
		    linePtr = linePtr->nextPtr;
		    i++;
		}
	    } else {
		register Node *childPtr;

		for (childPtr = nodePtr->children.nodePtr, i = 1;
			childPtr->nextPtr != NULL;
			childPtr = childPtr->nextPtr, i++) {
		    if (i <= firstChildren) {
			if (i == firstChildren) {
			    halfwayNodePtr = childPtr;
			}
		    }
		}
		childPtr->nextPtr = otherPtr->children.nodePtr;
		while (i <= firstChildren) {
		    halfwayNodePtr = childPtr;
		    childPtr = childPtr->nextPtr;
		    i++;
		}
	    }

	    /*
	     * If the two siblings can simply be merged together, do it.
	     */

	    if (totalChildren <= MAX_CHILDREN) {
		RecomputeNodeCounts(nodePtr);
		nodePtr->nextPtr = otherPtr->nextPtr;
		nodePtr->parentPtr->numChildren--;
		DeleteSummaries(otherPtr->summaryPtr);
		ckfree((char *) otherPtr);
		continue;
	    }

	    /*
	     * The siblings can't be merged, so just divide their
	     * children evenly between them.
	     */

	    if (nodePtr->level == 0) {
		otherPtr->children.linePtr = halfwayLinePtr->nextPtr;
		halfwayLinePtr->nextPtr = NULL;
	    } else {
		otherPtr->children.nodePtr = halfwayNodePtr->nextPtr;
		halfwayNodePtr->nextPtr = NULL;
	    }
	    RecomputeNodeCounts(nodePtr);
	    RecomputeNodeCounts(otherPtr);
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * RecomputeNodeCounts --
 *
 *	This procedure is called to recompute all the counts in a node
 *	(tags, child information, etc.) by scanning the information in
 *	its descendants.  This procedure is called during rebalancing
 *	when a node's child structure has changed.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The tag counts for nodePtr are modified to reflect its current
 *	child structure, as are its numChildren and numLines fields.
 *	Also, all of the childrens' parentPtr fields are made to point
 *	to nodePtr.
 *
 *----------------------------------------------------------------------
 */

static void
RecomputeNodeCounts(nodePtr)
    register Node *nodePtr;		/* Node whose tag summary information
					 * must be recomputed. */
{
    register Summary *summaryPtr, *summaryPtr2;
    register Node *childPtr;
    register TkTextLine *linePtr;
    register TkTextSegment *segPtr;
    TkTextTag *tagPtr;

    /*
     * Zero out all the existing counts for the node, but don't delete
     * the existing Summary records (most of them will probably be reused).
     */

    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL;
	    summaryPtr = summaryPtr->nextPtr) {
	summaryPtr->toggleCount = 0;
    }
    nodePtr->numChildren = 0;
    nodePtr->numLines = 0;

    /*
     * Scan through the children, adding the childrens' tag counts into
     * the node's tag counts and adding new Summary structures if
     * necessary.
     */

    if (nodePtr->level == 0) {
	for (linePtr = nodePtr->children.linePtr; linePtr != NULL;
		linePtr = linePtr->nextPtr) {
	    nodePtr->numChildren++;
	    nodePtr->numLines++;
	    linePtr->parentPtr = nodePtr;
	    for (segPtr = linePtr->segPtr; segPtr != NULL;
		    segPtr = segPtr->nextPtr) {
		if (((segPtr->typePtr != &tkTextToggleOnType)
			&& (segPtr->typePtr != &tkTextToggleOffType))
			|| !(segPtr->body.toggle.inNodeCounts)) {
		    continue;
		}
		tagPtr = segPtr->body.toggle.tagPtr;
		for (summaryPtr = nodePtr->summaryPtr; ;
			summaryPtr = summaryPtr->nextPtr) {
		    if (summaryPtr == NULL) {
			summaryPtr = (Summary *) ckalloc(sizeof(Summary));
			summaryPtr->tagPtr = tagPtr;
			summaryPtr->toggleCount = 1;
			summaryPtr->nextPtr = nodePtr->summaryPtr;
			nodePtr->summaryPtr = summaryPtr;
			break;
		    }
		    if (summaryPtr->tagPtr == tagPtr) {
			summaryPtr->toggleCount++;
			break;
		    }
		}
	    }
	}
    } else {
	for (childPtr = nodePtr->children.nodePtr; childPtr != NULL;
		childPtr = childPtr->nextPtr) {
	    nodePtr->numChildren++;
	    nodePtr->numLines += childPtr->numLines;
	    childPtr->parentPtr = nodePtr;
	    for (summaryPtr2 = childPtr->summaryPtr; summaryPtr2 != NULL;
		    summaryPtr2 = summaryPtr2->nextPtr) {
		for (summaryPtr = nodePtr->summaryPtr; ;
			summaryPtr = summaryPtr->nextPtr) {
		    if (summaryPtr == NULL) {
			summaryPtr = (Summary *) ckalloc(sizeof(Summary));
			summaryPtr->tagPtr = summaryPtr2->tagPtr;
			summaryPtr->toggleCount = summaryPtr2->toggleCount;
			summaryPtr->nextPtr = nodePtr->summaryPtr;
			nodePtr->summaryPtr = summaryPtr;
			break;
		    }
		    if (summaryPtr->tagPtr == summaryPtr2->tagPtr) {
			summaryPtr->toggleCount += summaryPtr2->toggleCount;
			break;
		    }
		}
	    }
	}
    }

    /*
     * Scan through the node's tag records again and delete any Summary
     * records that still have a zero count, or that have all the toggles.
     * The node with the children that account for all the tags toggles
     * have no summary information, and they become the tagRootPtr for the tag.
     */

    summaryPtr2 = NULL;
    for (summaryPtr = nodePtr->summaryPtr; summaryPtr != NULL; ) {
	if (summaryPtr->toggleCount > 0 && 
		summaryPtr->toggleCount < summaryPtr->tagPtr->toggleCount) {
	    if (nodePtr->level == summaryPtr->tagPtr->tagRootPtr->level) {
		/*
		 * The tag's root node split and some toggles left.
		 * The tag root must move up a level.
		 */
		summaryPtr->tagPtr->tagRootPtr = nodePtr->parentPtr;
	    }
	    summaryPtr2 = summaryPtr;
	    summaryPtr = summaryPtr->nextPtr;
	    continue;
	}
	if (summaryPtr->toggleCount == summaryPtr->tagPtr->toggleCount) {
	    /*
	     * A node merge has collected all the toggles under one node.
	     * Push the root down to this level.
	     */
	    summaryPtr->tagPtr->tagRootPtr = nodePtr;
	}
	if (summaryPtr2 != NULL) {
	    summaryPtr2->nextPtr = summaryPtr->nextPtr;
	    ckfree((char *) summaryPtr);
	    summaryPtr = summaryPtr2->nextPtr;
	} else {
	    nodePtr->summaryPtr = summaryPtr->nextPtr;
	    ckfree((char *) summaryPtr);
	    summaryPtr = nodePtr->summaryPtr;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeNumLines --
 *
 *	This procedure returns a count of the number of lines of
 *	text present in a given B-tree.
 *
 * Results:
 *	The return value is a count of the number of usable lines
 *	in tree (i.e. it doesn't include the dummy line that is just
 * 	used to mark the end of the tree).
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
TkBTreeNumLines(tree)
    TkTextBTree tree;			/* Information about tree. */
{
    BTree *treePtr = (BTree *) tree;
    return treePtr->rootPtr->numLines - 1;
}

/*
 *--------------------------------------------------------------
 *
 * CharSplitProc --
 *
 *	This procedure implements splitting for character segments.
 *
 * Results:
 *	The return value is a pointer to a chain of two segments
 *	that have the same characters as segPtr except split
 *	among the two segments.
 *
 * Side effects:
 *	Storage for segPtr is freed.
 *
 *--------------------------------------------------------------
 */

static TkTextSegment *
CharSplitProc(segPtr, index)
    TkTextSegment *segPtr;		/* Pointer to segment to split. */
    int index;				/* Position within segment at which
					 * to split. */
{
    TkTextSegment *newPtr1, *newPtr2;

    newPtr1 = (TkTextSegment *) ckalloc(CSEG_SIZE(index));
    newPtr2 = (TkTextSegment *) ckalloc(
	    CSEG_SIZE(segPtr->size - index));
    newPtr1->typePtr = &tkTextCharType;
    newPtr1->nextPtr = newPtr2;
    newPtr1->size = index;
    strncpy(newPtr1->body.chars, segPtr->body.chars, (size_t) index);
    newPtr1->body.chars[index] = 0;
    newPtr2->typePtr = &tkTextCharType;
    newPtr2->nextPtr = segPtr->nextPtr;
    newPtr2->size = segPtr->size - index;
    strcpy(newPtr2->body.chars, segPtr->body.chars + index);
    ckfree((char*) segPtr);
    return newPtr1;
}

/*
 *--------------------------------------------------------------
 *
 * CharCleanupProc --
 *
 *	This procedure merges adjacent character segments into
 *	a single character segment, if possible.
 *
 * Results:
 *	The return value is a pointer to the first segment in
 *	the (new) list of segments that used to start with segPtr.
 *
 * Side effects:
 *	Storage for the segments may be allocated and freed.
 *
 *--------------------------------------------------------------
 */

	/* ARGSUSED */
static TkTextSegment *
CharCleanupProc(segPtr, linePtr)
    TkTextSegment *segPtr;		/* Pointer to first of two adjacent
					 * segments to join. */
    TkTextLine *linePtr;		/* Line containing segments (not
					 * used). */
{
    TkTextSegment *segPtr2, *newPtr;

    segPtr2 = segPtr->nextPtr;
    if ((segPtr2 == NULL) || (segPtr2->typePtr != &tkTextCharType)) {
	return segPtr;
    }
    newPtr = (TkTextSegment *) ckalloc(CSEG_SIZE(
	    segPtr->size + segPtr2->size));
    newPtr->typePtr = &tkTextCharType;
    newPtr->nextPtr = segPtr2->nextPtr;
    newPtr->size = segPtr->size + segPtr2->size;
    strcpy(newPtr->body.chars, segPtr->body.chars);
    strcpy(newPtr->body.chars + segPtr->size, segPtr2->body.chars);
    ckfree((char*) segPtr);
    ckfree((char*) segPtr2);
    return newPtr;
}

/*
 *--------------------------------------------------------------
 *
 * CharDeleteProc --
 *
 *	This procedure is invoked to delete a character segment.
 *
 * Results:
 *	Always returns 0 to indicate that the segment was deleted.
 *
 * Side effects:
 *	Storage for the segment is freed.
 *
 *--------------------------------------------------------------
 */

	/* ARGSUSED */
static int
CharDeleteProc(segPtr, linePtr, treeGone)
    TkTextSegment *segPtr;		/* Segment to delete. */
    TkTextLine *linePtr;		/* Line containing segment. */
    int treeGone;			/* Non-zero means the entire tree is
					 * being deleted, so everything must
					 * get cleaned up. */
{
    ckfree((char*) segPtr);
    return 0;
}

/*
 *--------------------------------------------------------------
 *
 * CharCheckProc --
 *
 *	This procedure is invoked to perform consistency checks
 *	on character segments.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If the segment isn't inconsistent then the procedure
 *	panics.
 *
 *--------------------------------------------------------------
 */

	/* ARGSUSED */
static void
CharCheckProc(segPtr, linePtr)
    TkTextSegment *segPtr;		/* Segment to check. */
    TkTextLine *linePtr;		/* Line containing segment. */
{
    /*
     * Make sure that the segment contains the number of
     * characters indicated by its header, and that the last
     * segment in a line ends in a newline.  Also make sure
     * that there aren't ever two character segments adjacent
     * to each other:  they should be merged together.
     */

    if (segPtr->size <= 0) {
	panic("CharCheckProc: segment has size <= 0");
    }
    if (strlen(segPtr->body.chars) != (size_t) segPtr->size) {
	panic("CharCheckProc: segment has wrong size");
    }
    if (segPtr->nextPtr == NULL) {
	if (segPtr->body.chars[segPtr->size-1] != '\n') {
	    panic("CharCheckProc: line doesn't end with newline");
	}
    } else {
	if (segPtr->nextPtr->typePtr == &tkTextCharType) {
	    panic("CharCheckProc: adjacent character segments weren't merged");
	}
    }
}

/*
 *--------------------------------------------------------------
 *
 * ToggleDeleteProc --
 *
 *	This procedure is invoked to delete toggle segments.
 *
 * Results:
 *	Returns 1 to indicate that the segment may not be deleted,
 *	unless the entire B-tree is going away.
 *
 * Side effects:
 *	If the tree is going away then the toggle's memory is
 *	freed;  otherwise the toggle counts in nodes above the
 *	segment get updated.
 *
 *--------------------------------------------------------------
 */

static int
ToggleDeleteProc(segPtr, linePtr, treeGone)
    TkTextSegment *segPtr;		/* Segment to check. */
    TkTextLine *linePtr;		/* Line containing segment. */
    int treeGone;			/* Non-zero means the entire tree is
					 * being deleted, so everything must
					 * get cleaned up. */
{
    if (treeGone) {
	ckfree((char *) segPtr);
	return 0;
    }

    /*
     * This toggle is in the middle of a range of characters that's
     * being deleted.  Refuse to die.  We'll be moved to the end of
     * the deleted range and our cleanup procedure will be called
     * later.  Decrement node toggle counts here, and set a flag
     * so we'll re-increment them in the cleanup procedure.
     */

    if (segPtr->body.toggle.inNodeCounts) {
	ChangeNodeToggleCount(linePtr->parentPtr,
		segPtr->body.toggle.tagPtr, -1);
	segPtr->body.toggle.inNodeCounts = 0;
    }
    return 1;
}

/*
 *--------------------------------------------------------------
 *
 * ToggleCleanupProc --
 *
 *	This procedure is called when a toggle is part of a line that's
 *	been modified in some way.  It's invoked after the
 *	modifications are complete.
 *
 * Results:
 *	The return value is the head segment in a new list
 *	that is to replace the tail of the line that used to
 *	start at segPtr.  This allows the procedure to delete
 *	or modify segPtr.
 *
 * Side effects:
 *	Toggle counts in the nodes above the new line will be
 *	updated if they're not already.  Toggles may be collapsed
 *	if there are duplicate toggles at the same position.
 *
 *--------------------------------------------------------------
 */

static TkTextSegment *
ToggleCleanupProc(segPtr, linePtr)
    TkTextSegment *segPtr;	/* Segment to check. */
    TkTextLine *linePtr;	/* Line that now contains segment. */
{
    TkTextSegment *segPtr2, *prevPtr;
    int counts;

    /*
     * If this is a toggle-off segment, look ahead through the next
     * segments to see if there's a toggle-on segment for the same tag
     * before any segments with non-zero size.  If so then the two
     * toggles cancel each other;  remove them both.
     */

    if (segPtr->typePtr == &tkTextToggleOffType) {
	for (prevPtr = segPtr, segPtr2 = prevPtr->nextPtr;
		(segPtr2 != NULL) && (segPtr2->size == 0);
		prevPtr = segPtr2, segPtr2 = prevPtr->nextPtr) {
	    if (segPtr2->typePtr != &tkTextToggleOnType) {
		continue;
	    }
	    if (segPtr2->body.toggle.tagPtr != segPtr->body.toggle.tagPtr) {
		continue;
	    }
	    counts = segPtr->body.toggle.inNodeCounts
		    + segPtr2->body.toggle.inNodeCounts;
	    if (counts != 0) {
		ChangeNodeToggleCount(linePtr->parentPtr,
			segPtr->body.toggle.tagPtr, -counts);
	    }
	    prevPtr->nextPtr = segPtr2->nextPtr;
	    ckfree((char *) segPtr2);
	    segPtr2 = segPtr->nextPtr;
	    ckfree((char *) segPtr);
	    return segPtr2;
	}
    }

    if (!segPtr->body.toggle.inNodeCounts) {
	ChangeNodeToggleCount(linePtr->parentPtr,
		segPtr->body.toggle.tagPtr, 1);
	segPtr->body.toggle.inNodeCounts = 1;
    }
    return segPtr;
}

/*
 *--------------------------------------------------------------
 *
 * ToggleLineChangeProc --
 *
 *	This procedure is invoked when a toggle segment is about
 *	to move from one line to another.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Toggle counts are decremented in the nodes above the line.
 *
 *--------------------------------------------------------------
 */

static void
ToggleLineChangeProc(segPtr, linePtr)
    TkTextSegment *segPtr;	/* Segment to check. */
    TkTextLine *linePtr;	/* Line that used to contain segment. */
{
    if (segPtr->body.toggle.inNodeCounts) {
	ChangeNodeToggleCount(linePtr->parentPtr,
		segPtr->body.toggle.tagPtr, -1);
	segPtr->body.toggle.inNodeCounts = 0;
    }
}

/*
 *--------------------------------------------------------------
 *
 * ToggleCheckProc --
 *
 *	This procedure is invoked to perform consistency checks
 *	on toggle segments.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If a consistency problem is found the procedure panics.
 *
 *--------------------------------------------------------------
 */

static void
ToggleCheckProc(segPtr, linePtr)
    TkTextSegment *segPtr;		/* Segment to check. */
    TkTextLine *linePtr;		/* Line containing segment. */
{
    register Summary *summaryPtr;
    int needSummary;

    if (segPtr->size != 0) {
	panic("ToggleCheckProc: segment had non-zero size");
    }
    if (!segPtr->body.toggle.inNodeCounts) {
	panic("ToggleCheckProc: toggle counts not updated in nodes");
    }
    needSummary = (segPtr->body.toggle.tagPtr->tagRootPtr != linePtr->parentPtr);
    for (summaryPtr = linePtr->parentPtr->summaryPtr; ;
	    summaryPtr = summaryPtr->nextPtr) {
	if (summaryPtr == NULL) {
	    if (needSummary) {
		panic("ToggleCheckProc: tag not present in node");
	    } else {
		break;
	    }
	}
	if (summaryPtr->tagPtr == segPtr->body.toggle.tagPtr) {
	    if (!needSummary) {
		panic("ToggleCheckProc: tag present in root node summary");
	    }
	    break;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TkBTreeCharsInLine --
 *
 *	This procedure returns a count of the number of characters
 *	in a given line.
 *
 * Results:
 *	The return value is the character count for linePtr.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
TkBTreeCharsInLine(linePtr)
    TkTextLine *linePtr;		/* Line whose characters should be
					 * counted. */
{
    TkTextSegment *segPtr;
    int count;

    count = 0;
    for (segPtr = linePtr->segPtr; segPtr != NULL; segPtr = segPtr->nextPtr) {
	if (segPtr->typePtr == &tkTextCharType) {
	    count += Tcl_NumUtfChars(segPtr->body.chars, segPtr->size);
	} else {
	    count += segPtr->size;
	}
    }
    return count;
}

int
TkBTreeBytesInLine(linePtr)
    TkTextLine *linePtr;		/* Line whose characters should be
					 * counted. */
{
    TkTextSegment *segPtr;
    int count;

    count = 0;
    for (segPtr = linePtr->segPtr; segPtr != NULL; segPtr = segPtr->nextPtr) {
	count += segPtr->size;
    }
    return count;
}