path: root/generic/tclArithSeries.c

/*
 * tclArithSeries.c --
 *
 *     This file contains the ArithSeries concrete abstract list
 *     implementation. It implements the inner workings of the lseq command.
 *
 * Copyright © 2022 Brian S. Griffin.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"
#include "tclArithSeries.h"
#include <assert.h>
#include <math.h>

/* -------------------------- ArithSeries object ---------------------------- */


static inline ArithSeries* ArithSeriesRepPtr(Tcl_Obj *arithSeriesObjPtr)
{
    return (ArithSeries *)arithSeriesObjPtr->internalRep.twoPtrValue.ptr1;
}

static inline double ArithSeriesIndexDbl(
    ArithSeries *arithSeriesRepPtr,
    Tcl_WideInt index)
{
    ArithSeriesDbl *dblRepPtr = (ArithSeriesDbl*)arithSeriesRepPtr;
    if (arithSeriesRepPtr->isDouble) {
	return (dblRepPtr->start + ((index) * dblRepPtr->step));
    } else {
	return (double)(arithSeriesRepPtr->start + (index * arithSeriesRepPtr->step));
    }
}

static inline Tcl_WideInt ArithSeriesIndexInt(
    ArithSeries *arithSeriesRepPtr,
    Tcl_WideInt index)
{
    ArithSeriesDbl *dblRepPtr = (ArithSeriesDbl*)arithSeriesRepPtr;
    if (arithSeriesRepPtr->isDouble) {
	return (Tcl_WideInt)(dblRepPtr->start + ((index) * dblRepPtr->step));
    } else {
	return (arithSeriesRepPtr->start + (index * arithSeriesRepPtr->step));
    }
}

static inline ArithSeries *ArithSeriesGetInternalRep(Tcl_Obj *objPtr)
{
    const Tcl_ObjInternalRep *irPtr;
    irPtr = TclFetchInternalRep((objPtr), &tclArithSeriesType.objType);
    return irPtr ? (ArithSeries *)irPtr->twoPtrValue.ptr1 : NULL;
}


/*
 * Prototypes for procedures defined later in this file:
 */

static void		DupArithSeriesInternalRep (Tcl_Obj *srcPtr, Tcl_Obj *copyPtr);
static void		FreeArithSeriesInternalRep (Tcl_Obj *listPtr);
static int		SetArithSeriesFromAny (Tcl_Interp *interp, Tcl_Obj *objPtr);
static void		UpdateStringOfArithSeries (Tcl_Obj *arithSeriesObj);
static Tcl_Obj *ArithSeriesObjStep(Tcl_Obj *arithSeriesPtr);
static Tcl_Size ArithSeriesObjLength(Tcl_Obj *arithSeriesPtr);

/*
 * The structure below defines the arithmetic series Tcl object type by
 * means of procedures that can be invoked by generic object code.
 *
 * The arithmetic series object is a special case of Tcl list representing
 * an interval of an arithmetic series in constant space.
 *
 * The arithmetic series is internally represented with three integers,
 * *start*, *end*, and *step*, Where the length is calculated with
 * the following algorithm:
 *
 * if RANGE == 0 THEN
 *   ERROR
 * if RANGE > 0
 *   LEN is (((END-START)-1)/STEP) + 1
 * else if RANGE < 0
 *   LEN is (((END-START)-1)/STEP) - 1
 *
 * And where the equivalent's list I-th element is calculated
 * as:
 *
 * LIST[i] = START + (STEP * i)
 *
 * Zero elements ranges, like in the case of START=10 END=10 STEP=1
 * are valid and will be equivalent to the empty list.
 */

const TclObjTypeWithAbstractList tclArithSeriesType = {
    {"arithseries",			/* name */
    FreeArithSeriesInternalRep,		/* freeIntRepProc */
    DupArithSeriesInternalRep,		/* dupIntRepProc */
    UpdateStringOfArithSeries,		/* updateStringProc */
    SetArithSeriesFromAny,		/* setFromAnyProc */
    TCL_OBJTYPE_V0_1(
    ArithSeriesObjLength
    )}
};

/*
 *----------------------------------------------------------------------
 *
 * ArithSeriesLen --
 *
 * 	Compute the length of the equivalent list where
 * 	every element is generated starting from *start*,
 * 	and adding *step* to generate every successive element
 * 	that's < *end* for positive steps, or > *end* for negative
 * 	steps.
 *
 * Results:
 *
 * 	The length of the list generated by the given range,
 * 	that may be zero.
 * 	The function returns -1 if the list is of length infinite.
 *
 * Side effects:
 *
 * 	None.
 *
 *----------------------------------------------------------------------
 */
static Tcl_WideInt
ArithSeriesLen(Tcl_WideInt start, Tcl_WideInt end, Tcl_WideInt step)
{
    Tcl_WideInt len;

    if (step == 0) {
	return 0;
    }
    len = 1 + ((end-start)/step);
    return (len < 0) ? -1 : len;
}

/*
 *----------------------------------------------------------------------
 *
 * NewArithSeriesInt --
 *
 *	Creates a new ArithSeries object. The returned object has
 *	refcount = 0.
 *
 * Results:
 *
 * 	A Tcl_Obj pointer to the created ArithSeries object.
 * 	A NULL pointer of the range is invalid.
 *
 * Side Effects:
 *
 * 	None.
 *----------------------------------------------------------------------
 */
static
Tcl_Obj *
NewArithSeriesInt(Tcl_WideInt start, Tcl_WideInt end, Tcl_WideInt step, Tcl_WideInt len)
{
    Tcl_WideInt length = (len>=0 ? len : ArithSeriesLen(start, end, step));
    Tcl_Obj *arithSeriesObj;
    ArithSeries *arithSeriesRepPtr;

    TclNewObj(arithSeriesObj);

    if (length <= 0) {
	return arithSeriesObj;
    }

    arithSeriesRepPtr = (ArithSeries*) Tcl_Alloc(sizeof (ArithSeries));
    arithSeriesRepPtr->isDouble = 0;
    arithSeriesRepPtr->start = start;
    arithSeriesRepPtr->end = end;
    arithSeriesRepPtr->step = step;
    arithSeriesRepPtr->len = length;
    arithSeriesRepPtr->elements = NULL;
    arithSeriesObj->internalRep.twoPtrValue.ptr1 = arithSeriesRepPtr;
    arithSeriesObj->internalRep.twoPtrValue.ptr2 = NULL;
    arithSeriesObj->typePtr = &tclArithSeriesType.objType;
    if (length > 0)
    	Tcl_InvalidateStringRep(arithSeriesObj);

    return arithSeriesObj;
}

/*
 *----------------------------------------------------------------------
 *
 * NewArithSeriesDbl --
 *
 *	Creates a new ArithSeries object with doubles. The returned object has
 *	refcount = 0.
 *
 * Results:
 *
 * 	A Tcl_Obj pointer to the created ArithSeries object.
 * 	A NULL pointer of the range is invalid.
 *
 * Side Effects:
 *
 * 	None.
 *----------------------------------------------------------------------
 */
static
Tcl_Obj *
NewArithSeriesDbl(double start, double end, double step, Tcl_WideInt len)
{
    Tcl_WideInt length = (len>=0 ? len : ArithSeriesLen(start, end, step));
    Tcl_Obj *arithSeriesObj;
    ArithSeriesDbl *arithSeriesRepPtr;

    TclNewObj(arithSeriesObj);

    if (length <= 0) {
	return arithSeriesObj;
    }

    arithSeriesRepPtr = (ArithSeriesDbl*) Tcl_Alloc(sizeof (ArithSeriesDbl));
    arithSeriesRepPtr->isDouble = 1;
    arithSeriesRepPtr->start = start;
    arithSeriesRepPtr->end = end;
    arithSeriesRepPtr->step = step;
    arithSeriesRepPtr->len = length;
    arithSeriesRepPtr->elements = NULL;
    arithSeriesObj->internalRep.twoPtrValue.ptr1 = arithSeriesRepPtr;
    arithSeriesObj->internalRep.twoPtrValue.ptr2 = NULL;
    arithSeriesObj->typePtr = &tclArithSeriesType.objType;
    if (length > 0)
    	Tcl_InvalidateStringRep(arithSeriesObj);

    return arithSeriesObj;
}

/*
 *----------------------------------------------------------------------
 *
 * assignNumber --
 *
 *	Create the appropriate Tcl_Obj value for the given numeric values.
 *      Used locally only for decoding [lseq] numeric arguments.
 *	refcount = 0.
 *
 * Results:
 *
 * 	A Tcl_Obj pointer.
 *      No assignment on error.
 *
 * Side Effects:
 *
 * 	None.
 *----------------------------------------------------------------------
 */
static void
assignNumber(
    int useDoubles,
    Tcl_WideInt *intNumberPtr,
    double *dblNumberPtr,
    Tcl_Obj *numberObj)
{
    void *clientData;
    int tcl_number_type;

    if (Tcl_GetNumberFromObj(NULL, numberObj, &clientData, &tcl_number_type) != TCL_OK
	    || tcl_number_type == TCL_NUMBER_BIG) {
	return;
    }
    if (useDoubles) {
	if (tcl_number_type != TCL_NUMBER_INT) {
	    *dblNumberPtr = *(double *)clientData;
	} else {
	    *dblNumberPtr = (double)*(Tcl_WideInt *)clientData;
	}
    } else {
	if (tcl_number_type == TCL_NUMBER_INT) {
	    *intNumberPtr = *(Tcl_WideInt *)clientData;
	} else {
	    *intNumberPtr = (Tcl_WideInt)*(double *)clientData;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclNewArithSeriesObj --
 *
 *	Creates a new ArithSeries object. Some arguments may be NULL and will
 *	be computed based on the other given arguments.
 *      refcount = 0.
 *
 * Results:
 *
 * 	A Tcl_Obj pointer to the created ArithSeries object.
 * 	An empty Tcl_Obj if the range is invalid.
 *
 * Side Effects:
 *
 * 	None.
 *----------------------------------------------------------------------
 */

int
TclNewArithSeriesObj(
    Tcl_Interp *interp,       /* For error reporting */
    Tcl_Obj **arithSeriesObj, /* return value */
    int useDoubles,           /* Flag indicates values start,
			      ** end, step, are treated as doubles */
    Tcl_Obj *startObj,        /* Starting value */
    Tcl_Obj *endObj,          /* Ending limit */
    Tcl_Obj *stepObj,         /* increment value */
    Tcl_Obj *lenObj)          /* Number of elements */
{
    double dstart, dend, dstep;
    Tcl_WideInt start, end, step;
    Tcl_WideInt len;

    if (startObj) {
	assignNumber(useDoubles, &start, &dstart, startObj);
    } else {
	start = 0;
	dstart = start;
    }
    if (stepObj) {
	assignNumber(useDoubles, &step, &dstep, stepObj);
	if (useDoubles) {
	    step = dstep;
	} else {
	    dstep = step;
	}
	if (dstep == 0) {
	    *arithSeriesObj = Tcl_NewObj();
	    return TCL_OK;
	}
    }
    if (endObj) {
	assignNumber(useDoubles, &end, &dend, endObj);
    }
    if (lenObj) {
	if (TCL_OK != Tcl_GetWideIntFromObj(interp, lenObj, &len)) {
	    return TCL_ERROR;
	}
    }

    if (startObj && endObj) {
	if (!stepObj) {
	    if (useDoubles) {
		dstep = (dstart < dend) ? 1.0 : -1.0;
		step = dstep;
	    } else {
		step = (start < end) ? 1 : -1;
		dstep = step;
	    }
	}
	assert(dstep!=0);
	if (!lenObj) {
	    if (useDoubles) {
		len = (dend - dstart + dstep)/dstep;
	    } else {
		len = (end - start + step)/step;
	    }
	}
    }

    if (!endObj) {
	if (useDoubles) {
	    dend = dstart + (dstep * (len-1));
	    end = dend;
	} else {
	    end = start + (step * (len-1));
	    dend = end;
	}
    }

    if (TCL_MAJOR_VERSION < 9 && ((len > ListSizeT_MAX) || (len > LIST_MAX))) {
	Tcl_SetObjResult(
	    interp,
	    Tcl_NewStringObj("max length of a Tcl list exceeded", TCL_INDEX_NONE));
	Tcl_SetErrorCode(interp, "TCL", "MEMORY", NULL);
	return TCL_ERROR;
    }

    if (arithSeriesObj) {
	*arithSeriesObj = (useDoubles)
	    ? NewArithSeriesDbl(dstart, dend, dstep, len)
	    : NewArithSeriesInt(start, end, step, len);
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ArithSeriesObjStep --
 *
 *	Return a Tcl_Obj with the step value from the give ArithSeries Obj.
 *	refcount = 0.
 *
 * Results:
 *
 * 	A Tcl_Obj pointer to the created ArithSeries object.
 * 	A NULL pointer of the range is invalid.
 *
 * Side Effects:
 *
 * 	None.
 *----------------------------------------------------------------------
 */
Tcl_Obj *
ArithSeriesObjStep(
    Tcl_Obj *arithSeriesObj)
{
    ArithSeries *arithSeriesRepPtr;
    Tcl_Obj *stepObj;

    if (arithSeriesObj->typePtr != &tclArithSeriesType.objType) {
        Tcl_Panic("ArithSeriesObjStep called with a not ArithSeries Obj.");
    }
    arithSeriesRepPtr = ArithSeriesRepPtr(arithSeriesObj);
    if (arithSeriesRepPtr->isDouble) {
	TclNewDoubleObj(stepObj, ((ArithSeriesDbl*)(arithSeriesRepPtr))->step);
    } else {
	TclNewIntObj(stepObj, arithSeriesRepPtr->step);
    }
    return stepObj;
}


/*
 *----------------------------------------------------------------------
 *
 * TclArithSeriesObjIndex --
 *
 *	Returns the element with the specified index in the list
 *	represented by the specified Arithmetic Sequence object.
 *	If the index is out of range, NULL is returned.
 *
 * Results:
 *
 * 	The element on success, NULL on index out of range.
 *
 * Side Effects:
 *
 * 	On success, the integer pointed by *element is modified.
 *
 *----------------------------------------------------------------------
 */

Tcl_Obj *
TclArithSeriesObjIndex(
    Tcl_Interp *interp,
    Tcl_Obj *arithSeriesObj,
    Tcl_WideInt index)
{
    ArithSeries *arithSeriesRepPtr;

    if (arithSeriesObj->typePtr != &tclArithSeriesType.objType) {
	Tcl_Panic("TclArithSeriesObjIndex called with a not ArithSeries Obj.");
    }
    arithSeriesRepPtr = ArithSeriesRepPtr(arithSeriesObj);
    if (index < 0 || (Tcl_Size)index >= arithSeriesRepPtr->len) {
	return Tcl_NewObj();
    }
    /* List[i] = Start + (Step * index) */
    if (arithSeriesRepPtr->isDouble) {
	return Tcl_NewDoubleObj(ArithSeriesIndexDbl(arithSeriesRepPtr, index));
    } else {
	return Tcl_NewWideIntObj(ArithSeriesIndexInt(arithSeriesRepPtr, index));
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ArithSeriesObjLength
 *
 *	Returns the length of the arithmetic series.
 *
 * Results:
 *
 * 	The length of the series as Tcl_WideInt.
 *
 * Side Effects:
 *
 * 	None.
 *
 *----------------------------------------------------------------------
 */
Tcl_Size ArithSeriesObjLength(Tcl_Obj *arithSeriesObj)
{
    ArithSeries *arithSeriesRepPtr = (ArithSeries*)
	    arithSeriesObj->internalRep.twoPtrValue.ptr1;
    return arithSeriesRepPtr->len;
}

/*
 *----------------------------------------------------------------------
 *
 * FreeArithSeriesInternalRep --
 *
 *	Deallocate the storage associated with an arithseries object's
 *	internal representation.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Frees arithSeriesObj's ArithSeries* internal representation and
 *	sets listPtr's	internalRep.twoPtrValue.ptr1 to NULL.
 *
 *----------------------------------------------------------------------
 */

static void
FreeArithSeriesInternalRep(Tcl_Obj *arithSeriesObj)
{
    ArithSeries *arithSeriesRepPtr =
	    (ArithSeries *) arithSeriesObj->internalRep.twoPtrValue.ptr1;
    if (arithSeriesRepPtr->elements) {
	Tcl_Size i;
	Tcl_Obj**elmts = arithSeriesRepPtr->elements;
	for(i=0; i<arithSeriesRepPtr->len; i++) {
	    if (elmts[i]) {
		Tcl_DecrRefCount(elmts[i]);
	    }
	}
	Tcl_Free((char *) arithSeriesRepPtr->elements);
    }
    Tcl_Free((char *) arithSeriesRepPtr);
    arithSeriesObj->internalRep.twoPtrValue.ptr1 = NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * DupArithSeriesInternalRep --
 *
 *	Initialize the internal representation of a arithseries Tcl_Obj to a
 *	copy of the internal representation of an existing arithseries object.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	We set "copyPtr"s internal rep to a pointer to a
 *	newly allocated ArithSeries structure.
 *----------------------------------------------------------------------
 */

static void
DupArithSeriesInternalRep(
    Tcl_Obj *srcPtr,		/* Object with internal rep to copy. */
    Tcl_Obj *copyPtr)		/* Object with internal rep to set. */
{
    ArithSeries *srcArithSeriesRepPtr =
	    (ArithSeries *) srcPtr->internalRep.twoPtrValue.ptr1;
    ArithSeries *copyArithSeriesRepPtr;

    /*
     * Allocate a new ArithSeries structure. */

    copyArithSeriesRepPtr = (ArithSeries*) Tcl_Alloc(sizeof(ArithSeries));
    *copyArithSeriesRepPtr = *srcArithSeriesRepPtr;
    copyArithSeriesRepPtr->elements = NULL;
    copyPtr->internalRep.twoPtrValue.ptr1 = copyArithSeriesRepPtr;
    copyPtr->internalRep.twoPtrValue.ptr2 = NULL;
    copyPtr->typePtr = &tclArithSeriesType.objType;
}

/*
 *----------------------------------------------------------------------
 *
 * UpdateStringOfArithSeries --
 *
 *	Update the string representation for an arithseries object.
 *	Note: This procedure does not invalidate an existing old string rep
 *	so storage will be lost if this has not already been done.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The object's string is set to a valid string that results from
 *	the list-to-string conversion. This string will be empty if the
 *	list has no elements. The list internal representation
 *	should not be NULL and we assume it is not NULL.
 *
 * Notes:
 * 	At the cost of overallocation it's possible to estimate
 * 	the length of the string representation and make this procedure
 * 	much faster. Because the programmer shouldn't expect the
 * 	string conversion of a big arithmetic sequence to be fast
 * 	this version takes more care of space than time.
 *
 *----------------------------------------------------------------------
 */

static void
UpdateStringOfArithSeries(Tcl_Obj *arithSeriesObj)
{
    ArithSeries *arithSeriesRepPtr =
	    (ArithSeries*) arithSeriesObj->internalRep.twoPtrValue.ptr1;
    char *elem, *p;
    Tcl_Obj *elemObj;
    Tcl_Size i;
    Tcl_Size length = 0;
    size_t slen;

    /*
     * Pass 1: estimate space.
     */
    if (!arithSeriesRepPtr->isDouble) {
	for (i = 0; i < arithSeriesRepPtr->len; i++) {
	    double d = ArithSeriesIndexDbl(arithSeriesRepPtr, i);
	    slen = d>0 ? log10(d)+1 : d<0 ? log10((0-d))+2 : 1;
	    length += slen;
	}
    } else {
	for (i = 0; i < arithSeriesRepPtr->len; i++) {
	    double d = ArithSeriesIndexDbl(arithSeriesRepPtr, i);
	    char tmp[TCL_DOUBLE_SPACE+2];
	    tmp[0] = 0;
	    Tcl_PrintDouble(NULL,d,tmp);
	    if ((length + strlen(tmp)) >= TCL_SIZE_SMAX) {
		break; //
	    }
	    length += strlen(tmp);
	}
    }
    length += arithSeriesRepPtr->len; // Space for each separator

    /*
     * Pass 2: generate the string repr.
     */

    p = Tcl_InitStringRep(arithSeriesObj, NULL, length);
    if (p == NULL) {
	Tcl_Panic("Unable to allocate string size %" TCL_Z_MODIFIER "u", length);
    }
    for (i = 0; i < arithSeriesRepPtr->len; i++) {
	elemObj = TclArithSeriesObjIndex(NULL, arithSeriesObj, i);
	elem = Tcl_GetStringFromObj(elemObj, &slen);
	if (((p - arithSeriesObj->bytes)+slen) > length) {
	    break;
	}
	strcpy(p, elem);
	p[slen] = ' ';
	p += slen+1;
	Tcl_DecrRefCount(elemObj);
    }
    if (length > 0) arithSeriesObj->bytes[length-1] = '\0';
    arithSeriesObj->length = length-1;
}

/*
 *----------------------------------------------------------------------
 *
 * SetArithSeriesFromAny --
 *
 * 	The Arithmetic Series object is just an way to optimize
 * 	Lists space complexity, so no one should try to convert
 * 	a string to an Arithmetic Series object.
 *
 * 	This function is here just to populate the Type structure.
 *
 * Results:
 *
 * 	The result is always TCL_ERROR. But see Side Effects.
 *
 * Side effects:
 *
 * 	Tcl Panic if called.
 *
 *----------------------------------------------------------------------
 */

static int
SetArithSeriesFromAny(
    TCL_UNUSED(Tcl_Interp *),		/* Used for error reporting if not NULL. */
    TCL_UNUSED(Tcl_Obj *))		/* The object to convert. */
{
    Tcl_Panic("SetArithSeriesFromAny: should never be called");
    return TCL_ERROR;
}

/*
 *----------------------------------------------------------------------
 *
 * TclArithSeriesObjCopy --
 *
 *	Makes a "pure arithSeries" copy of an ArithSeries value. This provides for the C
 *	level a counterpart of the [lrange $list 0 end] command, while using
 *	internals details to be as efficient as possible.
 *
 * Results:
 *
 *	Normally returns a pointer to a new Tcl_Obj, that contains the same
 *	arithSeries value as *arithSeriesObj does. The returned Tcl_Obj has a
 *	refCount of zero. If *arithSeriesObj does not hold an arithSeries,
 *	NULL is returned, and if interp is non-NULL, an error message is
 *	recorded there.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_Obj *
TclArithSeriesObjCopy(
    Tcl_Interp *interp,		/* Used to report errors if not NULL. */
    Tcl_Obj *arithSeriesObj)	/* List object for which an element array is
				 * to be returned. */
{
    Tcl_Obj *copyPtr;
    ArithSeries *arithSeriesRepPtr;

    arithSeriesRepPtr = ArithSeriesGetInternalRep(arithSeriesObj);
    if (NULL == arithSeriesRepPtr) {
	if (SetArithSeriesFromAny(interp, arithSeriesObj) != TCL_OK) {
	    /* We know this is going to panic, but it's the message we want */
	    return NULL;
	}
    }

    TclNewObj(copyPtr);
    TclInvalidateStringRep(copyPtr);
    DupArithSeriesInternalRep(arithSeriesObj, copyPtr);
    return copyPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TclArithSeriesObjRange --
 *
 *	Makes a slice of an ArithSeries value.
 *      *arithSeriesObj must be known to be a valid list.
 *
 * Results:
 *	Returns a pointer to the sliced series.
 *      This may be a new object or the same object if not shared.
 *
 * Side effects:
 *	?The possible conversion of the object referenced by listPtr?
 *	?to a list object.?
 *
 *----------------------------------------------------------------------
 */

Tcl_Obj *
TclArithSeriesObjRange(
    Tcl_Interp *interp,         /* For error message(s) */
    Tcl_Obj *arithSeriesObj,	/* List object to take a range from. */
    Tcl_Size fromIdx,		/* Index of first element to include. */
    Tcl_Size toIdx)		/* Index of last element to include. */
{
    ArithSeries *arithSeriesRepPtr;
    Tcl_Obj *startObj, *endObj, *stepObj;

    arithSeriesRepPtr = ArithSeriesGetInternalRep(arithSeriesObj);

    if (fromIdx == TCL_INDEX_NONE) {
	fromIdx = 0;
    }
    
    if (fromIdx > toIdx ||
	(toIdx > arithSeriesRepPtr->len-1 &&
	 fromIdx > arithSeriesRepPtr->len-1)) {
	Tcl_Obj *obj;
	TclNewObj(obj);
	return obj;
    }
    
    if (fromIdx < 0) {
	fromIdx = 0;
    }
    if (toIdx < 0) {
	toIdx = 0;
    }
    if (toIdx > arithSeriesRepPtr->len-1) {
	toIdx = arithSeriesRepPtr->len-1;
    }

    startObj = TclArithSeriesObjIndex(interp, arithSeriesObj, fromIdx);
    if (startObj == NULL) {
	return NULL;
    }
    Tcl_IncrRefCount(startObj);
    endObj = TclArithSeriesObjIndex(interp, arithSeriesObj, toIdx);
    if (endObj == NULL) {
	return NULL;
    }
    Tcl_IncrRefCount(endObj);
    stepObj = ArithSeriesObjStep(arithSeriesObj);
    Tcl_IncrRefCount(stepObj);

    if (Tcl_IsShared(arithSeriesObj) ||
	    ((arithSeriesObj->refCount > 1))) {
	Tcl_Obj *newSlicePtr;
	if (TclNewArithSeriesObj(interp, &newSlicePtr,
	        arithSeriesRepPtr->isDouble, startObj, endObj,
		stepObj, NULL) != TCL_OK) {
	    newSlicePtr = NULL;
	}
	Tcl_DecrRefCount(startObj);
	Tcl_DecrRefCount(endObj);
	Tcl_DecrRefCount(stepObj);
	return newSlicePtr;
    }

    /*
     * In-place is possible.
     */

    /*
     * Even if nothing below causes any changes, we still want the
     * string-canonizing effect of [lrange 0 end].
     */

    TclInvalidateStringRep(arithSeriesObj);

    if (arithSeriesRepPtr->isDouble) {
	ArithSeriesDbl *arithSeriesDblRepPtr = (ArithSeriesDbl*)arithSeriesRepPtr;
	double start, end, step;
	Tcl_GetDoubleFromObj(NULL, startObj, &start);
	Tcl_GetDoubleFromObj(NULL, endObj, &end);
	Tcl_GetDoubleFromObj(NULL, stepObj, &step);
	arithSeriesDblRepPtr->start = start;
	arithSeriesDblRepPtr->end = end;
	arithSeriesDblRepPtr->step = step;
	arithSeriesDblRepPtr->len = (end-start+step)/step;
	arithSeriesDblRepPtr->elements = NULL;

    } else {
	Tcl_WideInt start, end, step;
	Tcl_GetWideIntFromObj(NULL, startObj, &start);
	Tcl_GetWideIntFromObj(NULL, endObj, &end);
	Tcl_GetWideIntFromObj(NULL, stepObj, &step);
	arithSeriesRepPtr->start = start;
	arithSeriesRepPtr->end = end;
	arithSeriesRepPtr->step = step;
	arithSeriesRepPtr->len = (end-start+step)/step;
	arithSeriesRepPtr->elements = NULL;
    }

    Tcl_DecrRefCount(startObj);
    Tcl_DecrRefCount(endObj);
    Tcl_DecrRefCount(stepObj);

    return arithSeriesObj;
}

/*
 *----------------------------------------------------------------------
 *
 * TclArithSeriesGetElements --
 *
 *	This function returns an (objc,objv) array of the elements in a list
 *	object.
 *
 * Results:
 *	The return value is normally TCL_OK; in this case *objcPtr is set to
 *	the count of list elements and *objvPtr is set to a pointer to an
 *	array of (*objcPtr) pointers to each list element. If listPtr does not
 *	refer to an Abstract List object and the object can not be converted
 *	to one, TCL_ERROR is returned and an error message will be left in the
 *	interpreter's result if interp is not NULL.
 *
 *	The objects referenced by the returned array should be treated as
 *	readonly and their ref counts are _not_ incremented; the caller must
 *	do that if it holds on to a reference. Furthermore, the pointer and
 *	length returned by this function may change as soon as any function is
 *	called on the list object; be careful about retaining the pointer in a
 *	local data structure.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
TclArithSeriesGetElements(
    Tcl_Interp *interp,		/* Used to report errors if not NULL. */
    Tcl_Obj *objPtr,		/* ArithSeries object for which an element
				 * array is to be returned. */
    Tcl_Size *objcPtr,		/* Where to store the count of objects
				 * referenced by objv. */
    Tcl_Obj ***objvPtr)		/* Where to store the pointer to an array of
				 * pointers to the list's objects. */
{
    if (TclHasInternalRep(objPtr,&tclArithSeriesType.objType)) {
	ArithSeries *arithSeriesRepPtr;
	Tcl_Obj **objv;
	int i, objc;

	arithSeriesRepPtr = ArithSeriesGetInternalRep(objPtr);
	objc = arithSeriesRepPtr->len;
	if (objc > 0) {
	    if (arithSeriesRepPtr->elements) {
		/* If this exists, it has already been populated */
		objv = arithSeriesRepPtr->elements;
	    } else {
		/* Construct the elements array */
		objv = (Tcl_Obj **)Tcl_Alloc(sizeof(Tcl_Obj*) * objc);
		if (objv == NULL) {
		    if (interp) {
			Tcl_SetObjResult(
			    interp,
			    Tcl_NewStringObj("max length of a Tcl list exceeded", TCL_INDEX_NONE));
			Tcl_SetErrorCode(interp, "TCL", "MEMORY", NULL);
		    }
		    return TCL_ERROR;
		}
		arithSeriesRepPtr->elements = objv;
		for (i = 0; i < objc; i++) {
		    objv[i] = TclArithSeriesObjIndex(interp, objPtr, i);
		    if (objv[i] == NULL) {
			return TCL_ERROR;
		    }
		    Tcl_IncrRefCount(objv[i]);
		}
	    }
	} else {
	    objv = NULL;
	}
	*objvPtr = objv;
	*objcPtr = objc;
    } else {
	if (interp != NULL) {
	    Tcl_SetObjResult(
		interp,
		Tcl_ObjPrintf("value is not an arithseries"));
	    Tcl_SetErrorCode(interp, "TCL", "VALUE", "UNKNOWN", NULL);
	}
	return TCL_ERROR;
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * TclArithSeriesObjReverse --
 *
 *	Reverse the order of the ArithSeries value.
 *      *arithSeriesObj must be known to be a valid list.
 *
 * Results:
 *	Returns a pointer to the reordered series.
 *      This may be a new object or the same object if not shared.
 *
 * Side effects:
 *	?The possible conversion of the object referenced by listPtr?
 *	?to a list object.?
 *
 *----------------------------------------------------------------------
 */

Tcl_Obj *
TclArithSeriesObjReverse(
    Tcl_Interp *interp,         /* For error message(s) */
    Tcl_Obj *arithSeriesObj)	/* List object to reverse. */
{
    ArithSeries *arithSeriesRepPtr;
    Tcl_Obj *startObj, *endObj, *stepObj;
    Tcl_Obj *resultObj;
    Tcl_WideInt start, end, step, len;
    double dstart, dend, dstep;
    int isDouble;

    arithSeriesRepPtr = ArithSeriesGetInternalRep(arithSeriesObj);

    isDouble = arithSeriesRepPtr->isDouble;
    len = arithSeriesRepPtr->len;

    startObj = TclArithSeriesObjIndex(NULL, arithSeriesObj, (len-1));
    Tcl_IncrRefCount(startObj);
    endObj = TclArithSeriesObjIndex(NULL, arithSeriesObj, 0);
    Tcl_IncrRefCount(endObj);
    stepObj = ArithSeriesObjStep(arithSeriesObj);
    Tcl_IncrRefCount(stepObj);

    if (isDouble) {
	Tcl_GetDoubleFromObj(NULL, startObj, &dstart);
	Tcl_GetDoubleFromObj(NULL, endObj, &dend);
	Tcl_GetDoubleFromObj(NULL, stepObj, &dstep);
	dstep = -dstep;
	TclSetDoubleObj(stepObj, dstep);
    } else {
	Tcl_GetWideIntFromObj(NULL, startObj, &start);
	Tcl_GetWideIntFromObj(NULL, endObj, &end);
	Tcl_GetWideIntFromObj(NULL, stepObj, &step);
	step = -step;
	TclSetIntObj(stepObj, step);
    }

    if (Tcl_IsShared(arithSeriesObj) ||
	    ((arithSeriesObj->refCount > 1))) {
	Tcl_Obj *lenObj;
	TclNewIntObj(lenObj, len);
	if (TclNewArithSeriesObj(interp, &resultObj,
		 isDouble, startObj, endObj, stepObj, lenObj) != TCL_OK) {
	    resultObj = NULL;
	}
	Tcl_DecrRefCount(lenObj);
    } else {

	/*
	 * In-place is possible.
	 */

	TclInvalidateStringRep(arithSeriesObj);

	if (isDouble) {
	    ArithSeriesDbl *arithSeriesDblRepPtr =
		(ArithSeriesDbl*)arithSeriesRepPtr;
	    arithSeriesDblRepPtr->start = dstart;
	    arithSeriesDblRepPtr->end = dend;
	    arithSeriesDblRepPtr->step = dstep;
	} else {
	    arithSeriesRepPtr->start = start;
	    arithSeriesRepPtr->end = end;
	    arithSeriesRepPtr->step = step;
	}
	if (arithSeriesRepPtr->elements) {
	    Tcl_WideInt i;
	    for (i=0; i<len; i++) {
		Tcl_DecrRefCount(arithSeriesRepPtr->elements[i]);
	    }
	    Tcl_Free((char*)arithSeriesRepPtr->elements);
	}
	arithSeriesRepPtr->elements = NULL;

	resultObj = arithSeriesObj;
    }

    Tcl_DecrRefCount(startObj);
    Tcl_DecrRefCount(endObj);
    Tcl_DecrRefCount(stepObj);

    return resultObj;
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */