* generic/tkImgGIF.c (StringWriteGIF): Added ability to write a GIF to

	a string (as a byte array, of course) following comments on c.l.t by
	Aric Bills. Also improved readability of some of the function and
	field names in this file.


FossilOrigin-Name: 0c405ec30a2eb72407163618553c05568570942b

1 files changed, 370 insertions, 318 deletions

diff --git a/generic/tkImgGIF.c b/generic/tkImgGIF.c
index b7bb956..0ece066 100644
--- a/generic/tkImgGIF.c
+++ b/generic/tkImgGIF.c
@@ -11,7 +11,7 @@
  * Copyright (c) Reed Wade (wade@cs.utk.edu), University of Tennessee
  * Copyright (c) 1995-1997 Sun Microsystems, Inc.
  * Copyright (c) 1997 Australian National University
- * Copyright (c) 2005 Donal K. Fellows
+ * Copyright (c) 2005-2010 Donal K. Fellows
  *
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
@@ -29,7 +29,7 @@
  * |   provided "as is" without express or implied warranty.		|
  * +--------------------------------------------------------------------+
  *
- * RCS: @(#) $Id: tkImgGIF.c,v 1.47 2010/04/23 08:32:56 nijtmans Exp $
+ * RCS: @(#) $Id: tkImgGIF.c,v 1.48 2010/07/18 23:58:17 dkf Exp $
  */
 
 #include "tkInt.h"
@@ -109,6 +109,14 @@ typedef struct {
 } GIFImageConfig;
 
 /*
+ * Type of a function used to do the writing to a file or buffer when
+ * serializing in the GIF format.
+ */
+
+typedef int (WriteBytesFunc) (ClientData clientData, const char *bytes,
+			    int byteCount);
+
+/*
  * The format record for the GIF file format:
  */
 
@@ -127,8 +135,11 @@ static int		StringReadGIF(Tcl_Interp *interp, Tcl_Obj *dataObj,
 			    int srcX, int srcY);
 static int		FileWriteGIF(Tcl_Interp *interp, const char *filename,
 			    Tcl_Obj *format, Tk_PhotoImageBlock *blockPtr);
-static int		CommonWriteGIF(Tcl_Interp *interp, Tcl_Channel handle,
-			    Tcl_Obj *format, Tk_PhotoImageBlock *blockPtr);
+static int		StringWriteGIF(Tcl_Interp *interp, Tcl_Obj *format,
+			    Tk_PhotoImageBlock *blockPtr);
+static int		CommonWriteGIF(Tcl_Interp *interp, ClientData clientData,
+			    WriteBytesFunc *writeProc, Tcl_Obj *format,
+			    Tk_PhotoImageBlock *blockPtr);
 
 Tk_PhotoImageFormat tkImgFmtGIF = {
     "gif",		/* name */
@@ -137,7 +148,7 @@ Tk_PhotoImageFormat tkImgFmtGIF = {
     FileReadGIF,	/* fileReadProc */
     StringReadGIF,	/* stringReadProc */
     FileWriteGIF,	/* fileWriteProc */
-    NULL,		/* stringWriteProc */
+    StringWriteGIF,	/* stringWriteProc */
     NULL
 };
 
@@ -186,6 +197,135 @@ static int		Mgetc(MFile *handle);
 static int		char64(int c);
 static void		mInit(unsigned char *string, MFile *handle,
 			    int length);
+
+/*
+ * Types, defines and variables needed to write and compress a GIF.
+ */
+
+#define LSB(a)		((unsigned char) (((short)(a)) & 0x00FF))
+#define MSB(a)		((unsigned char) (((short)(a)) >> 8))
+
+#define GIFBITS		12
+#define HSIZE		5003	/* 80% occupancy */
+
+#define DEFAULT_BACKGROUND_VALUE	0xD9
+
+typedef struct {
+    int ssize;
+    int csize;
+    int rsize;
+    unsigned char *pixelOffset;
+    int pixelSize;
+    int pixelPitch;
+    int greenOffset;
+    int blueOffset;
+    int alphaOffset;
+    int num;
+    unsigned char mapa[MAXCOLORMAPSIZE][3];
+} GifWriterState;
+
+typedef int (* ifunptr) (GifWriterState *statePtr);
+
+/*
+ * Support for compression of GIFs.
+ */
+
+#define MAXCODE(numBits)	(((long) 1 << (numBits)) - 1)
+
+#ifdef SIGNED_COMPARE_SLOW
+#define U(x)	((unsigned) (x))
+#else
+#define U(x)	(x)
+#endif
+
+typedef struct {
+    int numBits;		/* Number of bits/code. */
+    long maxCode;		/* Maximum code, given numBits. */
+    int hashTable[HSIZE];
+    unsigned int codeTable[HSIZE];
+    long hSize;			/* For dynamic table sizing. */
+
+    /*
+     * To save much memory, we overlay the table used by compress() with those
+     * used by decompress(). The tab_prefix table is the same size and type as
+     * the codeTable. The tab_suffix table needs 2**GIFBITS characters. We get
+     * this from the beginning of hashTable. The output stack uses the rest of
+     * hashTable, and contains characters. There is plenty of room for any
+     * possible stack (stack used to be 8000 characters).
+     */
+
+    int freeEntry;		/* First unused entry. */
+
+    /*
+     * Block compression parameters.  After all codes are used up, and
+     * compression rate changes, start over.
+     */
+
+    int clearFlag;
+
+    int offset;
+    unsigned int inCount;	/* Length of input */
+    unsigned int outCount;	/* # of codes output (for debugging) */
+
+    /*
+     * Algorithm: use open addressing double hashing (no chaining) on the
+     * prefix code / next character combination. We do a variant of Knuth's
+     * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
+     * secondary probe. Here, the modular division first probe is gives way to
+     * a faster exclusive-or manipulation. Also do block compression with an
+     * adaptive reset, whereby the code table is cleared when the compression
+     * ratio decreases, but after the table fills. The variable-length output
+     * codes are re-sized at this point, and a special CLEAR code is generated
+     * for the decompressor. Late addition: construct the table according to
+     * file size for noticeable speed improvement on small files. Please
+     * direct questions about this implementation to ames!jaw.
+     */
+
+    int initialBits;
+    ClientData destination;
+    WriteBytesFunc *writeProc;
+
+    int clearCode;
+    int eofCode;
+
+    unsigned long currentAccumulated;
+    int currentBits;
+
+    /*
+     * Number of characters so far in this 'packet'
+     */
+
+    int accumulatedByteCount;
+
+    /*
+     * Define the storage for the packet accumulator
+     */
+
+    unsigned char packetAccumulator[256];
+} GIFState_t;
+
+/*
+ * Definition of new functions to write GIFs
+ */
+
+static int		ColorNumber(GifWriterState *statePtr,
+			    int red, int green, int blue);
+static void		Compress(int initBits, ClientData handle,
+			    WriteBytesFunc *writeProc, ifunptr readValue,
+			    GifWriterState *statePtr);
+static int		IsNewColor(GifWriterState *statePtr,
+			    int red, int green, int blue);
+static void		SaveMap(GifWriterState *statePtr,
+			    Tk_PhotoImageBlock *blockPtr);
+static int		ReadValue(GifWriterState *statePtr);
+static WriteBytesFunc	WriteToChannel;
+static WriteBytesFunc	WriteToByteArray;
+static void		Output(GIFState_t *statePtr, long code);
+static void		ClearForBlock(GIFState_t *statePtr);
+static void		ClearHashTable(GIFState_t *statePtr, int hSize);
+static void		CharInit(GIFState_t *statePtr);
+static void		CharOut(GIFState_t *statePtr, int c);
+static void		FlushChar(GIFState_t *statePtr);
 
 /*
  *----------------------------------------------------------------------
@@ -1424,51 +1564,12 @@ Fread(
  *	data from a photo image into a given file
  *
  * Results:
- *	A standard TCL completion code.  If TCL_ERROR is returned
- *	then an error message is left in the interp's result.
+ *	A standard TCL completion code.  If TCL_ERROR is returned then an
+ *	error message is left in the interp's result.
  *
  *----------------------------------------------------------------------
  */
 
-/*
- * Types, defines and variables needed to write and compress a GIF.
- */
-
-#define LSB(a)		((unsigned char) (((short)(a)) & 0x00FF))
-#define MSB(a)		((unsigned char) (((short)(a)) >> 8))
-
-#define GIFBITS		12
-#define HSIZE		5003	/* 80% occupancy */
-
-typedef struct {
-    int ssize;
-    int csize;
-    int rsize;
-    unsigned char *pixelo;
-    int pixelSize;
-    int pixelPitch;
-    int greenOffset;
-    int blueOffset;
-    int alphaOffset;
-    int num;
-    unsigned char mapa[MAXCOLORMAPSIZE][3];
-} GifWriterState;
-
-typedef int (* ifunptr) (GifWriterState *statePtr);
-
-/*
- * Definition of new functions to write GIFs
- */
-
-static int		color(GifWriterState *statePtr,
-			    int red, int green, int blue);
-static void		compress(int initBits, Tcl_Channel handle,
-			    ifunptr readValue, GifWriterState *statePtr);
-static int		nuevo(GifWriterState *statePtr,
-			    int red, int green, int blue);
-static void		savemap(GifWriterState *statePtr,
-			    Tk_PhotoImageBlock *blockPtr);
-static int		ReadValue(GifWriterState *statePtr);
 
 static int
 FileWriteGIF(
@@ -1490,18 +1591,65 @@ FileWriteGIF(
 	return TCL_ERROR;
     }
 
-    result = CommonWriteGIF(interp, chan, format, blockPtr);
+    result = CommonWriteGIF(interp, chan, WriteToChannel, format, blockPtr);
 
     if (Tcl_Close(interp, chan) == TCL_ERROR) {
 	return TCL_ERROR;
     }
     return result;
 }
+
+static int
+StringWriteGIF(
+    Tcl_Interp *interp,		/* Interpreter to use for reporting errors and
+				 * returning the GIF data. */
+    Tcl_Obj *format,
+    Tk_PhotoImageBlock *blockPtr)
+{
+    int result;
+    Tcl_Obj *objPtr = Tcl_NewObj();
+
+    Tcl_IncrRefCount(objPtr);
+    result = CommonWriteGIF(interp, objPtr, WriteToByteArray, format,
+	    blockPtr);
+    if (result == TCL_OK) {
+	Tcl_SetObjResult(interp, objPtr);
+    }
+    Tcl_DecrRefCount(objPtr);
+    return result;
+}
+
+static int
+WriteToChannel(
+    ClientData clientData,
+    const char *bytes,
+    int byteCount)
+{
+    Tcl_Channel handle = clientData;
+
+    return Tcl_Write(handle, bytes, byteCount);
+}
+
+static int
+WriteToByteArray(
+    ClientData clientData,
+    const char *bytes,
+    int byteCount)
+{
+    Tcl_Obj *objPtr = clientData;
+    Tcl_Obj *tmpObj = Tcl_NewByteArrayObj((unsigned char *) bytes, byteCount);
+
+    Tcl_IncrRefCount(tmpObj);
+    Tcl_AppendObjToObj(objPtr, tmpObj);
+    Tcl_DecrRefCount(tmpObj);
+    return byteCount;
+}
 
 static int
 CommonWriteGIF(
     Tcl_Interp *interp,
-    Tcl_Channel handle,
+    ClientData handle,
+    WriteBytesFunc *writeProc,
     Tcl_Obj *format,
     Tk_PhotoImageBlock *blockPtr)
 {
@@ -1529,7 +1677,7 @@ CommonWriteGIF(
 	state.alphaOffset = 0;
     }
 
-    Tcl_Write(handle, (char *) (state.alphaOffset ? GIF89a : GIF87a), 6);
+    writeProc(handle, (char *) (state.alphaOffset ? GIF89a : GIF87a), 6);
 
     for (x = 0; x < MAXCOLORMAPSIZE ;x++) {
 	state.mapa[x][CM_RED] = 255;
@@ -1539,9 +1687,9 @@ CommonWriteGIF(
 
     width = blockPtr->width;
     height = blockPtr->height;
-    state.pixelo = blockPtr->pixelPtr + blockPtr->offset[0];
+    state.pixelOffset = blockPtr->pixelPtr + blockPtr->offset[0];
     state.pixelPitch = blockPtr->pitch;
-    savemap(&state, blockPtr);
+    SaveMap(&state, blockPtr);
     if (state.num >= MAXCOLORMAPSIZE) {
 	Tcl_AppendResult(interp, "too many colors", NULL);
 	return TCL_ERROR;
@@ -1550,20 +1698,20 @@ CommonWriteGIF(
 	state.num = 2;
     }
     c = LSB(width);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = MSB(width);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = LSB(height);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = MSB(height);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     resolution = 0;
     while (state.num >> resolution) {
 	resolution++;
     }
     c = 111 + resolution * 17;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     state.num = 1 << resolution;
 
@@ -1572,21 +1720,21 @@ CommonWriteGIF(
      */
 
     c = 0;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     /*
      * Zero for future expansion.
      */
 
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     for (x = 0; x < state.num; x++) {
 	c = state.mapa[x][CM_RED];
-	Tcl_Write(handle, (char *) &c, 1);
+	writeProc(handle, (char *) &c, 1);
 	c = state.mapa[x][CM_GREEN];
-	Tcl_Write(handle, (char *) &c, 1);
+	writeProc(handle, (char *) &c, 1);
 	c = state.mapa[x][CM_BLUE];
-	Tcl_Write(handle, (char *) &c, 1);
+	writeProc(handle, (char *) &c, 1);
     }
 
     /*
@@ -1595,50 +1743,50 @@ CommonWriteGIF(
 
     if (state.alphaOffset) {
 	c = GIF_EXTENSION;
-	Tcl_Write(handle, (char *) &c, 1);
-	Tcl_Write(handle, "\371\4\1\0\0\0", 7);
+	writeProc(handle, (char *) &c, 1);
+	writeProc(handle, "\371\4\1\0\0\0", 7);
     }
 
     c = GIF_START;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = LSB(top);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = MSB(top);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = LSB(left);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = MSB(left);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     c = LSB(width);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = MSB(width);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     c = LSB(height);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = MSB(height);
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     c = 0;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = resolution;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     state.ssize = state.rsize = blockPtr->width;
     state.csize = blockPtr->height;
-    compress(resolution+1, handle, ReadValue, &state);
+    Compress(resolution+1, handle, writeProc, ReadValue, &state);
 
     c = 0;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
     c = GIF_TERMINATOR;
-    Tcl_Write(handle, (char *) &c, 1);
+    writeProc(handle, (char *) &c, 1);
 
     return TCL_OK;
 }
 
 static int
-color(
+ColorNumber(
     GifWriterState *statePtr,
     int red, int green, int blue)
 {
@@ -1655,7 +1803,7 @@ color(
 }
 
 static int
-nuevo(
+IsNewColor(
     GifWriterState *statePtr,
     int red, int green, int blue)
 {
@@ -1672,7 +1820,7 @@ nuevo(
 }
 
 static void
-savemap(
+SaveMap(
     GifWriterState *statePtr,
     Tk_PhotoImageBlock *blockPtr)
 {
@@ -1682,9 +1830,9 @@ savemap(
 
     if (statePtr->alphaOffset) {
 	statePtr->num = 0;
-	statePtr->mapa[0][CM_RED] = 0xd9;
-	statePtr->mapa[0][CM_GREEN] = 0xd9;
-	statePtr->mapa[0][CM_BLUE] = 0xd9;
+	statePtr->mapa[0][CM_RED] = DEFAULT_BACKGROUND_VALUE;
+	statePtr->mapa[0][CM_GREEN] = DEFAULT_BACKGROUND_VALUE;
+	statePtr->mapa[0][CM_BLUE] = DEFAULT_BACKGROUND_VALUE;
     } else {
 	statePtr->num = -1;
     }
@@ -1696,7 +1844,7 @@ savemap(
 		red = colores[0];
 		green = colores[statePtr->greenOffset];
 		blue = colores[statePtr->blueOffset];
-		if (nuevo(statePtr, red, green, blue)) {
+		if (IsNewColor(statePtr, red, green, blue)) {
 		    statePtr->num++;
 		    if (statePtr->num >= MAXCOLORMAPSIZE) {
 			return;
@@ -1720,18 +1868,19 @@ ReadValue(
     if (statePtr->csize == 0) {
 	return EOF;
     }
-    if (statePtr->alphaOffset && (statePtr->pixelo[statePtr->alphaOffset]==0)) {
+    if (statePtr->alphaOffset
+	    && (statePtr->pixelOffset[statePtr->alphaOffset]==0)) {
 	col = 0;
     } else {
-	col = color(statePtr, statePtr->pixelo[0],
-		statePtr->pixelo[statePtr->greenOffset],
-		statePtr->pixelo[statePtr->blueOffset]);
+	col = ColorNumber(statePtr, statePtr->pixelOffset[0],
+		statePtr->pixelOffset[statePtr->greenOffset],
+		statePtr->pixelOffset[statePtr->blueOffset]);
     }
-    statePtr->pixelo += statePtr->pixelSize;
+    statePtr->pixelOffset += statePtr->pixelSize;
     if (--statePtr->ssize <= 0) {
 	statePtr->ssize = statePtr->rsize;
 	statePtr->csize--;
-	statePtr->pixelo += statePtr->pixelPitch
+	statePtr->pixelOffset += statePtr->pixelPitch
 		- (statePtr->rsize * statePtr->pixelSize);
     }
 
@@ -1739,7 +1888,7 @@ ReadValue(
 }
 
 /*
- * GIF Image compression - modified 'compress'
+ * GIF Image compression - modified 'Compress'
  *
  * Based on: compress.c - File compression ala IEEE Computer, June 1984.
  *
@@ -1750,192 +1899,98 @@ ReadValue(
  *              James A. Woods          (decvax!ihnp4!ames!jaw)
  *              Joe Orost               (decvax!vax135!petsd!joe)
  */
-
-#define MAXCODE(n_bits)		(((long) 1 << (n_bits)) - 1)
-
-typedef struct {
-    int n_bits;			/* number of bits/code */
-    long maxcode;		/* maximum code, given n_bits */
-    int htab[HSIZE];
-    unsigned int codetab[HSIZE];
-    long hsize;			/* for dynamic table sizing */
-
-    /*
-     * To save much memory, we overlay the table used by compress() with those
-     * used by decompress(). The tab_prefix table is the same size and type as
-     * the codetab. The tab_suffix table needs 2**GIFBITS characters. We get
-     * this from the beginning of htab. The output stack uses the rest of
-     * htab, and contains characters. There is plenty of room for any possible
-     * stack (stack used to be 8000 characters).
-     */
-
-    int free_ent;		/* first unused entry */
-
-    /*
-     * block compression parameters -- after all codes are used up,
-     * and compression rate changes, start over.
-     */
-
-    int clear_flg;
-
-    int offset;
-    unsigned int in_count;	/* length of input */
-    unsigned int out_count;	/* # of codes output (for debugging) */
-
-    /*
-     * compress stdin to stdout
-     *
-     * Algorithm: use open addressing double hashing (no chaining) on the
-     * prefix code / next character combination. We do a variant of Knuth's
-     * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
-     * secondary probe. Here, the modular division first probe is gives way to
-     * a faster exclusive-or manipulation. Also do block compression with an
-     * adaptive reset, whereby the code table is cleared when the compression
-     * ratio decreases, but after the table fills. The variable-length output
-     * codes are re-sized at this point, and a special CLEAR code is generated
-     * for the decompressor. Late addition: construct the table according to
-     * file size for noticeable speed improvement on small files. Please
-     * direct questions about this implementation to ames!jaw.
-     */
-
-    int g_init_bits;
-    Tcl_Channel g_outfile;
-
-    int ClearCode;
-    int EOFCode;
-
-    unsigned long cur_accum;
-    int cur_bits;
-
-    /*
-     * Number of characters so far in this 'packet'
-     */
-
-    int a_count;
-
-    /*
-     * Define the storage for the packet accumulator
-     */
-
-    unsigned char accum[256];
-} GIFState_t;
-
-static void		output(GIFState_t *statePtr, long code);
-static void		cl_block(GIFState_t *statePtr);
-static void		cl_hash(GIFState_t *statePtr, int hsize);
-static void		char_init(GIFState_t *statePtr);
-static void		char_out(GIFState_t *statePtr, int c);
-static void		flush_char(GIFState_t *statePtr);
-static void		compress(int initBits, Tcl_Channel handle,
-			    ifunptr readValue, GifWriterState *statePtr);
 
 static void
-compress(
-    int init_bits,
-    Tcl_Channel handle,
+Compress(
+    int initialBits,
+    ClientData handle,
+    WriteBytesFunc *writeProc,
     ifunptr readValue,
     GifWriterState *statePtr)
 {
-    register long fcode;
-    register long i = 0;
-    register int c;
-    register long ent;
-    register long disp;
-    register long hsize_reg;
-    register int hshift;
+    long fcode, ent, disp, hSize, i = 0;
+    int c, hshift;
     GIFState_t state;
 
     memset(&state, 0, sizeof(state));
 
     /*
-     * Set up the globals:  g_init_bits - initial number of bits
-     *			    g_outfile	- pointer to output file
+     * Set up the globals:  initialBits - initial number of bits
+     *			    outChannel	- pointer to output file
      */
 
-    state.g_init_bits = init_bits;
-    state.g_outfile = handle;
+    state.initialBits = initialBits;
+    state.destination = handle;
+    state.writeProc = writeProc;
 
     /*
      * Set up the necessary values.
      */
 
     state.offset = 0;
-    state.hsize = HSIZE;
-    state.out_count = 0;
-    state.clear_flg = 0;
-    state.in_count = 1;
-    state.maxcode = MAXCODE(state.n_bits = state.g_init_bits);
-
-    state.ClearCode = (1 << (init_bits - 1));
-    state.EOFCode = state.ClearCode + 1;
-    state.free_ent = state.ClearCode + 2;
-
-    char_init(&state);
+    state.hSize = HSIZE;
+    state.outCount = 0;
+    state.clearFlag = 0;
+    state.inCount = 1;
+    state.maxCode = MAXCODE(state.numBits = state.initialBits);
+    state.clearCode = 1 << (initialBits - 1);
+    state.eofCode = state.clearCode + 1;
+    state.freeEntry = state.clearCode + 2;
+    CharInit(&state);
 
     ent = readValue(statePtr);
 
     hshift = 0;
-    for (fcode = (long) state.hsize;  fcode < 65536L;  fcode *= 2L) {
+    for (fcode = (long) state.hSize;  fcode < 65536L;  fcode *= 2L) {
 	hshift++;
     }
-    hshift = 8 - hshift;			/* set hash code range bound */
+    hshift = 8 - hshift;		/* Set hash code range bound */
 
-    hsize_reg = state.hsize;
-    cl_hash(&state, (int) hsize_reg);		/* clear hash table */
+    hSize = state.hSize;
+    ClearHashTable(&state, (int) hSize); /* Clear hash table */
 
-    output(&state, (long) state.ClearCode);
+    Output(&state, (long) state.clearCode);
 
-#ifdef SIGNED_COMPARE_SLOW
-    while ((c = readValue(statePtr)) != (unsigned) EOF)
-#else
-    while ((c = readValue(statePtr)) != EOF)
-#endif
-    {
-	state.in_count++;
+    while (U(c = readValue(statePtr)) != U(EOF)) {
+	state.inCount++;
 
 	fcode = (long) (((long) c << GIFBITS) + ent);
-	i = (((long)c << hshift) ^ ent);	/* xor hashing */
+	i = ((long)c << hshift) ^ ent;	/* XOR hashing */
 
-	if (state.htab[i] == fcode) {
-	    ent = state.codetab[i];
+	if (state.hashTable[i] == fcode) {
+	    ent = state.codeTable[i];
 	    continue;
-	} else if ((long) state.htab[i] < 0) {	/* empty slot */
+	} else if ((long) state.hashTable[i] < 0) {	/* Empty slot */
 	    goto nomatch;
 	}
 
-	disp = hsize_reg - i;			/* secondary hash (after G.
-						 * Knott) */
+	disp = hSize - i;		/* Secondary hash (after G. Knott) */
 	if (i == 0) {
 	    disp = 1;
 	}
 
     probe:
 	if ((i -= disp) < 0) {
-	    i += hsize_reg;
+	    i += hSize;
 	}
 
-	if (state.htab[i] == fcode) {
-	    ent = state.codetab[i];
+	if (state.hashTable[i] == fcode) {
+	    ent = state.codeTable[i];
 	    continue;
 	}
-	if ((long) state.htab[i] > 0) {
+	if ((long) state.hashTable[i] > 0) {
 	    goto probe;
 	}
 
     nomatch:
-	output(&state, (long) ent);
-	state.out_count++;
+	Output(&state, (long) ent);
+	state.outCount++;
 	ent = c;
-#ifdef SIGNED_COMPARE_SLOW
-	if ((unsigned) free_ent < (unsigned) ((long)1 << GIFBITS))
-#else
-	if (state.free_ent < ((long)1 << GIFBITS))
-#endif
-	{
-	    state.codetab[i] = state.free_ent++; /* code -> hashtable */
-	    state.htab[i] = fcode;
+	if (U(state.freeEntry) < U((long)1 << GIFBITS)) {
+	    state.codeTable[i] = state.freeEntry++; /* code -> hashtable */
+	    state.hashTable[i] = fcode;
 	} else {
-	    cl_block(&state);
+	    ClearForBlock(&state);
 	}
     }
 
@@ -1943,91 +1998,87 @@ compress(
      * Put out the final code.
      */
 
-    output(&state, (long)ent);
-    state.out_count++;
-    output(&state, (long) state.EOFCode);
-
-    return;
+    Output(&state, (long) ent);
+    state.outCount++;
+    Output(&state, (long) state.eofCode);
 }
 
 /*****************************************************************
- * TAG( output )
+ * Output --
+ *	Output the given code.
  *
- * Output the given code.
  * Inputs:
- *	code:	A n_bits-bit integer. If == -1, then EOF. This assumes that
- *		n_bits =< (long) wordsize - 1.
+ *	code:	A numBits-bit integer. If == -1, then EOF. This assumes that
+ *		numBits =< (long) wordsize - 1.
  * Outputs:
  *	Outputs code to the file.
  * Assumptions:
  *	Chars are 8 bits long.
  * Algorithm:
- *	Maintain a GIFBITS character long buffer (so that 8 codes will
- * fit in it exactly).	Use the VAX insv instruction to insert each
- * code in turn.  When the buffer fills up empty it and start over.
+ *	Maintain a GIFBITS character long buffer (so that 8 codes will fit in
+ *	it exactly). Use the VAX insv instruction to insert each code in turn.
+ *	When the buffer fills up empty it and start over.
  */
 
-static const
-unsigned long masks[] = {
-    0x0000,
-    0x0001, 0x0003, 0x0007, 0x000F,
-    0x001F, 0x003F, 0x007F, 0x00FF,
-    0x01FF, 0x03FF, 0x07FF, 0x0FFF,
-    0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
-};
-
 static void
-output(
+Output(
     GIFState_t *statePtr,
     long code)
 {
-    statePtr->cur_accum &= masks[statePtr->cur_bits];
+    static const unsigned long masks[] = {
+	0x0000,
+	0x0001, 0x0003, 0x0007, 0x000F,
+	0x001F, 0x003F, 0x007F, 0x00FF,
+	0x01FF, 0x03FF, 0x07FF, 0x0FFF,
+	0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
+    };
 
-    if (statePtr->cur_bits > 0) {
-	statePtr->cur_accum |= ((long) code << statePtr->cur_bits);
+    statePtr->currentAccumulated &= masks[statePtr->currentBits];
+    if (statePtr->currentBits > 0) {
+	statePtr->currentAccumulated |= ((long) code << statePtr->currentBits);
     } else {
-	statePtr->cur_accum = code;
+	statePtr->currentAccumulated = code;
     }
+    statePtr->currentBits += statePtr->numBits;
 
-    statePtr->cur_bits += statePtr->n_bits;
-
-    while (statePtr->cur_bits >= 8 ) {
-	char_out(statePtr, (unsigned) (statePtr->cur_accum & 0xff));
-	statePtr->cur_accum >>= 8;
-	statePtr->cur_bits -= 8;
+    while (statePtr->currentBits >= 8) {
+	CharOut(statePtr, (unsigned) (statePtr->currentAccumulated & 0xff));
+	statePtr->currentAccumulated >>= 8;
+	statePtr->currentBits -= 8;
     }
 
     /*
-     * If the next entry is going to be too big for the code size,
-     * then increase it, if possible.
+     * If the next entry is going to be too big for the code size, then
+     * increase it, if possible.
      */
 
-    if ((statePtr->free_ent > statePtr->maxcode)|| statePtr->clear_flg ) {
-	if (statePtr->clear_flg) {
-	    statePtr->maxcode = MAXCODE(
-		    statePtr->n_bits = statePtr->g_init_bits);
-	    statePtr->clear_flg = 0;
+    if ((statePtr->freeEntry > statePtr->maxCode) || statePtr->clearFlag) {
+	if (statePtr->clearFlag) {
+	    statePtr->maxCode = MAXCODE(
+		    statePtr->numBits = statePtr->initialBits);
+	    statePtr->clearFlag = 0;
 	} else {
-	    statePtr->n_bits++;
-	    if (statePtr->n_bits == GIFBITS) {
-		statePtr->maxcode = (long)1 << GIFBITS;
+	    statePtr->numBits++;
+	    if (statePtr->numBits == GIFBITS) {
+		statePtr->maxCode = (long)1 << GIFBITS;
 	    } else {
-		statePtr->maxcode = MAXCODE(statePtr->n_bits);
+		statePtr->maxCode = MAXCODE(statePtr->numBits);
 	    }
 	}
     }
 
-    if (code == statePtr->EOFCode) {
+    if (code == statePtr->eofCode) {
 	/*
 	 * At EOF, write the rest of the buffer.
 	 */
 
-	while (statePtr->cur_bits > 0) {
-	    char_out(statePtr, (unsigned) (statePtr->cur_accum & 0xff));
-	    statePtr->cur_accum >>= 8;
-	    statePtr->cur_bits -= 8;
+	while (statePtr->currentBits > 0) {
+	    CharOut(statePtr,
+		    (unsigned) (statePtr->currentAccumulated & 0xff));
+	    statePtr->currentAccumulated >>= 8;
+	    statePtr->currentBits -= 8;
 	}
-	flush_char(statePtr);
+	FlushChar(statePtr);
     }
 }
 
@@ -2036,48 +2087,48 @@ output(
  */
 
 static void
-cl_block(			/* table clear for block compress */
+ClearForBlock(			/* Table clear for block compress. */
     GIFState_t *statePtr)
 {
-    cl_hash(statePtr, (int) statePtr->hsize);
-    statePtr->free_ent = statePtr->ClearCode + 2;
-    statePtr->clear_flg = 1;
+    ClearHashTable(statePtr, (int) statePtr->hSize);
+    statePtr->freeEntry = statePtr->clearCode + 2;
+    statePtr->clearFlag = 1;
 
-    output(statePtr, (long) statePtr->ClearCode);
+    Output(statePtr, (long) statePtr->clearCode);
 }
 
 static void
-cl_hash(			/* reset code table */
+ClearHashTable(			/* Reset code table. */
     GIFState_t *statePtr,
-    int hsize)
+    int hSize)
 {
-    register int *htab_p = statePtr->htab + hsize;
+    register int *hashTablePtr = statePtr->hashTable + hSize;
     register long i;
     register long m1 = -1;
 
-    i = hsize - 16;
+    i = hSize - 16;
     do {			/* might use Sys V memset(3) here */
-	*(htab_p-16) = m1;
-	*(htab_p-15) = m1;
-	*(htab_p-14) = m1;
-	*(htab_p-13) = m1;
-	*(htab_p-12) = m1;
-	*(htab_p-11) = m1;
-	*(htab_p-10) = m1;
-	*(htab_p-9) = m1;
-	*(htab_p-8) = m1;
-	*(htab_p-7) = m1;
-	*(htab_p-6) = m1;
-	*(htab_p-5) = m1;
-	*(htab_p-4) = m1;
-	*(htab_p-3) = m1;
-	*(htab_p-2) = m1;
-	*(htab_p-1) = m1;
-	htab_p -= 16;
+	*(hashTablePtr-16) = m1;
+	*(hashTablePtr-15) = m1;
+	*(hashTablePtr-14) = m1;
+	*(hashTablePtr-13) = m1;
+	*(hashTablePtr-12) = m1;
+	*(hashTablePtr-11) = m1;
+	*(hashTablePtr-10) = m1;
+	*(hashTablePtr-9) = m1;
+	*(hashTablePtr-8) = m1;
+	*(hashTablePtr-7) = m1;
+	*(hashTablePtr-6) = m1;
+	*(hashTablePtr-5) = m1;
+	*(hashTablePtr-4) = m1;
+	*(hashTablePtr-3) = m1;
+	*(hashTablePtr-2) = m1;
+	*(hashTablePtr-1) = m1;
+	hashTablePtr -= 16;
     } while ((i -= 16) >= 0);
 
     for (i += 16; i > 0; i--) {
-	*--htab_p = m1;
+	*--hashTablePtr = m1;
     }
 }
 
@@ -2094,12 +2145,12 @@ cl_hash(			/* reset code table */
  */
 
 static void
-char_init(
+CharInit(
     GIFState_t *statePtr)
 {
-    statePtr->a_count = 0;
-    statePtr->cur_accum = 0;
-    statePtr->cur_bits = 0;
+    statePtr->accumulatedByteCount = 0;
+    statePtr->currentAccumulated = 0;
+    statePtr->currentBits = 0;
 }
 
 /*
@@ -2108,13 +2159,13 @@ char_init(
  */
 
 static void
-char_out(
+CharOut(
     GIFState_t *statePtr,
     int c)
 {
-    statePtr->accum[statePtr->a_count++] = c;
-    if (statePtr->a_count >= 254) {
-	flush_char(statePtr);
+    statePtr->packetAccumulator[statePtr->accumulatedByteCount++] = c;
+    if (statePtr->accumulatedByteCount >= 254) {
+	FlushChar(statePtr);
     }
 }
 
@@ -2123,17 +2174,18 @@ char_out(
  */
 
 static void
-flush_char(
+FlushChar(
     GIFState_t *statePtr)
 {
     unsigned char c;
 
-    if (statePtr->a_count > 0) {
-	c = statePtr->a_count;
-	Tcl_Write(statePtr->g_outfile, (const char *) &c, 1);
-	Tcl_Write(statePtr->g_outfile, (const char *) statePtr->accum,
-		statePtr->a_count);
-	statePtr->a_count = 0;
+    if (statePtr->accumulatedByteCount > 0) {
+	c = statePtr->accumulatedByteCount;
+	statePtr->writeProc(statePtr->destination, (const char *) &c, 1);
+	statePtr->writeProc(statePtr->destination,
+		(const char *) statePtr->packetAccumulator,
+		statePtr->accumulatedByteCount);
+	statePtr->accumulatedByteCount = 0;
     }
 }