145 lines
3.6 KiB
C
145 lines
3.6 KiB
C
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// template qsort adapted from msdev\crt\src\qsort.c
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// created 7/96 bobp
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// template<class T>
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// void QSort (T *base, unsigned nEl, BOOL fSortUp)
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//
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// quicksort array of T
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//
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// Uses class T member functions:
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// operator =
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// operator <=
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#ifndef __TQSORT_INCL
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#define __TQSORT_INCL
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template<class T>
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inline void Swap(T &a, T &b)
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{
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T x = a; a = b; b = x;
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}
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template<class T>
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static void __cdecl ShortSort (T *lo, T *hi, BOOL fUp)
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{
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T *p, *max;
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while (hi > lo) {
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max = lo;
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if (fUp) {
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for (p = lo+1; p <= hi; p++) {
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if ( !(*p <= *max) )
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max = p;
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}
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} else {
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for (p = lo+1; p <= hi; p++) {
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if ( !(*max <= *p) )
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max = p;
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}
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}
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Swap (*max, *hi);
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hi --;
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}
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}
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#define CUTOFF 8 /* testing shows that this is good value */
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template<class T>
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void QSort (T *base, unsigned nEl, BOOL fUp)
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{
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T *lo, *hi; /* ends of sub-array currently sorting */
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T *mid; /* points to middle of subarray */
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T *loguy, *higuy; /* traveling pointers for partition step */
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unsigned size; /* size of the sub-array */
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T *lostk[30], *histk[30];
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int stkptr; /* stack for saving sub-array to be processed */
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/* Note: the number of stack entries required is no more than
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1 + log2(size), so 30 is sufficient for any array */
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if (nEl < 2)
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return; /* nothing to do */
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stkptr = 0; /* initialize stack */
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lo = base;
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hi = base + (nEl-1); /* initialize limits */
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recurse:
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size = (int)(hi - lo) + 1; /* number of el's to sort */
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if (size <= CUTOFF) {
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ShortSort(lo, hi, fUp);
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}
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else {
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mid = lo + (size / 2); /* find middle element */
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Swap(*mid, *lo); /* swap it to beginning of array */
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loguy = lo;
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higuy = hi + 1;
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for (;;) {
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if (fUp) {
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do {
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loguy ++;
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} while (loguy <= hi && *loguy <= *lo);
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do {
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higuy --;
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} while (higuy > lo && *lo <= *higuy);
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} else {
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do {
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loguy ++;
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} while (loguy <= hi && *lo <= *loguy);
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do {
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higuy --;
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} while (higuy > lo && *higuy <= *lo);
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}
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if (higuy < loguy)
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break;
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Swap(*loguy, *higuy);
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}
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Swap(*lo, *higuy); /* put partition element in place */
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if ( higuy - 1 - lo >= hi - loguy ) {
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if (lo + 1 < higuy) {
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lostk[stkptr] = lo;
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histk[stkptr] = higuy - 1;
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++stkptr;
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} /* save big recursion for later */
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if (loguy < hi) {
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lo = loguy;
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goto recurse; /* do small recursion */
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}
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}
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else {
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if (loguy < hi) {
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lostk[stkptr] = loguy;
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histk[stkptr] = hi;
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++stkptr; /* save big recursion for later */
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}
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if (lo + 1 < higuy) {
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hi = higuy - 1;
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goto recurse; /* do small recursion */
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}
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}
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}
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--stkptr;
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if (stkptr >= 0) {
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lo = lostk[stkptr];
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hi = histk[stkptr];
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goto recurse; /* pop subarray from stack */
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}
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}
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#endif
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