You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
383 lines
13 KiB
383 lines
13 KiB
/***
|
|
*qsort.c - quicksort algorithm; qsort() library function for sorting arrays
|
|
*
|
|
* Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
|
|
*
|
|
*Purpose:
|
|
* To implement the qsort() routine for sorting arrays.
|
|
*
|
|
*Revision History:
|
|
* 06-22-84 RN author
|
|
* 03-25-85 RN added pre-check for elements already in order to
|
|
* eliminate worst-case behavior.
|
|
* 05-18-86 TC changed to recurse on the smallest piece to avoid
|
|
* piece. unneccesary stack usage, and to iterate on
|
|
* largest
|
|
* 01-09-87 BCM fixed huge-array case where (num-1) * wid computation
|
|
* was overflowing (large/compact models only)
|
|
* 06-13-89 PHG made more efficient, many more comments, removed
|
|
* recursion
|
|
* 10-30-89 JCR Added _cdecl to prototypes
|
|
* 03-15-90 GJF Replaced _cdecl with _CALLTYPE1 and added #include
|
|
* <cruntime.h>. Also, fixed the copyright.
|
|
* 04-05-90 GJF Made shortsort() and swap() _CALLTYPE4. Also, added
|
|
* #include <search.h>.
|
|
* 10-04-90 GJF New-style function declarators.
|
|
* 12-28-90 SRW Added _CRUISER_ conditional around check_stack pragmas
|
|
* 01-24-91 SRW Added missing close comment in swap procedure
|
|
* 11-19-91 GJF Do the swap one character at a time to avoid alignment
|
|
* woes.
|
|
* 04-06-93 SKS Replace _CRTAPI* with __cdecl
|
|
* 09-06-94 CFW Remove Cruiser support.
|
|
* 02-27-98 RKP Add 64 bit support.
|
|
* 01-04-99 GJF Changes for 64-bit size_t.
|
|
* 05-10-00 PML Performance improvements - middle-of-3 pivot choice,
|
|
* widen middle range equal to pivot, don't swap pivot to
|
|
* beginning (vs7#99674).
|
|
* 08-08-00 PML Avoid calling comp(p,p), since some existing code
|
|
* doesn't expect that (vs7#123134).
|
|
*
|
|
*******************************************************************************/
|
|
|
|
#include <stdlib.h>
|
|
#include <search.h>
|
|
#ifdef NEW_QSORT_NAME
|
|
#define qsort NEW_QSORT_NAME
|
|
#endif
|
|
|
|
/* Always compile this module for speed, not size */
|
|
#pragma optimize("t", on)
|
|
|
|
/* prototypes for local routines */
|
|
static void __cdecl shortsort(char *lo, char *hi, size_t width,
|
|
int (__cdecl *comp)(const void *, const void *));
|
|
static void __cdecl swap(char *p, char *q, size_t width);
|
|
|
|
/* this parameter defines the cutoff between using quick sort and
|
|
insertion sort for arrays; arrays with lengths shorter or equal to the
|
|
below value use insertion sort */
|
|
|
|
#define CUTOFF 8 /* testing shows that this is good value */
|
|
|
|
/***
|
|
*qsort(base, num, wid, comp) - quicksort function for sorting arrays
|
|
*
|
|
*Purpose:
|
|
* quicksort the array of elements
|
|
* side effects: sorts in place
|
|
* maximum array size is number of elements times size of elements,
|
|
* but is limited by the virtual address space of the processor
|
|
*
|
|
*Entry:
|
|
* char *base = pointer to base of array
|
|
* size_t num = number of elements in the array
|
|
* size_t width = width in bytes of each array element
|
|
* int (*comp)() = pointer to function returning analog of strcmp for
|
|
* strings, but supplied by user for comparing the array elements.
|
|
* it accepts 2 pointers to elements and returns neg if 1<2, 0 if
|
|
* 1=2, pos if 1>2.
|
|
*
|
|
*Exit:
|
|
* returns void
|
|
*
|
|
*Exceptions:
|
|
*
|
|
*******************************************************************************/
|
|
|
|
/* sort the array between lo and hi (inclusive) */
|
|
|
|
#define STKSIZ (8*sizeof(void*) - 2)
|
|
|
|
void __cdecl qsort (
|
|
void *base,
|
|
size_t num,
|
|
size_t width,
|
|
int (__cdecl *comp)(const void *, const void *)
|
|
)
|
|
{
|
|
/* Note: the number of stack entries required is no more than
|
|
1 + log2(num), so 30 is sufficient for any array */
|
|
char *lo, *hi; /* ends of sub-array currently sorting */
|
|
char *mid; /* points to middle of subarray */
|
|
char *loguy, *higuy; /* traveling pointers for partition step */
|
|
size_t size; /* size of the sub-array */
|
|
char *lostk[STKSIZ], *histk[STKSIZ];
|
|
int stkptr; /* stack for saving sub-array to be processed */
|
|
|
|
if (num < 2 || width == 0)
|
|
return; /* nothing to do */
|
|
|
|
stkptr = 0; /* initialize stack */
|
|
|
|
lo = (char *)base;
|
|
hi = (char *)base + width * (num-1); /* initialize limits */
|
|
|
|
/* this entry point is for pseudo-recursion calling: setting
|
|
lo and hi and jumping to here is like recursion, but stkptr is
|
|
preserved, locals aren't, so we preserve stuff on the stack */
|
|
recurse:
|
|
|
|
size = (hi - lo) / width + 1; /* number of el's to sort */
|
|
|
|
/* below a certain size, it is faster to use a O(n^2) sorting method */
|
|
if (size <= CUTOFF) {
|
|
shortsort(lo, hi, width, comp);
|
|
}
|
|
else {
|
|
/* First we pick a partitioning element. The efficiency of the
|
|
algorithm demands that we find one that is approximately the median
|
|
of the values, but also that we select one fast. We choose the
|
|
median of the first, middle, and last elements, to avoid bad
|
|
performance in the face of already sorted data, or data that is made
|
|
up of multiple sorted runs appended together. Testing shows that a
|
|
median-of-three algorithm provides better performance than simply
|
|
picking the middle element for the latter case. */
|
|
|
|
mid = lo + (size / 2) * width; /* find middle element */
|
|
|
|
/* Sort the first, middle, last elements into order */
|
|
if (comp(lo, mid) > 0) {
|
|
swap(lo, mid, width);
|
|
}
|
|
if (comp(lo, hi) > 0) {
|
|
swap(lo, hi, width);
|
|
}
|
|
if (comp(mid, hi) > 0) {
|
|
swap(mid, hi, width);
|
|
}
|
|
|
|
/* We now wish to partition the array into three pieces, one consisting
|
|
of elements <= partition element, one of elements equal to the
|
|
partition element, and one of elements > than it. This is done
|
|
below; comments indicate conditions established at every step. */
|
|
|
|
loguy = lo;
|
|
higuy = hi;
|
|
|
|
/* Note that higuy decreases and loguy increases on every iteration,
|
|
so loop must terminate. */
|
|
for (;;) {
|
|
/* lo <= loguy < hi, lo < higuy <= hi,
|
|
A[i] <= A[mid] for lo <= i <= loguy,
|
|
A[i] > A[mid] for higuy <= i < hi,
|
|
A[hi] >= A[mid] */
|
|
|
|
/* The doubled loop is to avoid calling comp(mid,mid), since some
|
|
existing comparison funcs don't work when passed the same
|
|
value for both pointers. */
|
|
|
|
if (mid > loguy) {
|
|
do {
|
|
loguy += width;
|
|
} while (loguy < mid && comp(loguy, mid) <= 0);
|
|
}
|
|
if (mid <= loguy) {
|
|
do {
|
|
loguy += width;
|
|
} while (loguy <= hi && comp(loguy, mid) <= 0);
|
|
}
|
|
|
|
/* lo < loguy <= hi+1, A[i] <= A[mid] for lo <= i < loguy,
|
|
either loguy > hi or A[loguy] > A[mid] */
|
|
|
|
do {
|
|
higuy -= width;
|
|
} while (higuy > mid && comp(higuy, mid) > 0);
|
|
|
|
/* lo <= higuy < hi, A[i] > A[mid] for higuy < i < hi,
|
|
either higuy == lo or A[higuy] <= A[mid] */
|
|
|
|
if (higuy < loguy)
|
|
break;
|
|
|
|
/* if loguy > hi or higuy == lo, then we would have exited, so
|
|
A[loguy] > A[mid], A[higuy] <= A[mid],
|
|
loguy <= hi, higuy > lo */
|
|
|
|
swap(loguy, higuy, width);
|
|
|
|
/* If the partition element was moved, follow it. Only need
|
|
to check for mid == higuy, since before the swap,
|
|
A[loguy] > A[mid] implies loguy != mid. */
|
|
|
|
if (mid == higuy)
|
|
mid = loguy;
|
|
|
|
/* A[loguy] <= A[mid], A[higuy] > A[mid]; so condition at top
|
|
of loop is re-established */
|
|
}
|
|
|
|
/* A[i] <= A[mid] for lo <= i < loguy,
|
|
A[i] > A[mid] for higuy < i < hi,
|
|
A[hi] >= A[mid]
|
|
higuy < loguy
|
|
implying:
|
|
higuy == loguy-1
|
|
or higuy == hi - 1, loguy == hi + 1, A[hi] == A[mid] */
|
|
|
|
/* Find adjacent elements equal to the partition element. The
|
|
doubled loop is to avoid calling comp(mid,mid), since some
|
|
existing comparison funcs don't work when passed the same value
|
|
for both pointers. */
|
|
|
|
higuy += width;
|
|
if (mid < higuy) {
|
|
do {
|
|
higuy -= width;
|
|
} while (higuy > mid && comp(higuy, mid) == 0);
|
|
}
|
|
if (mid >= higuy) {
|
|
do {
|
|
higuy -= width;
|
|
} while (higuy > lo && comp(higuy, mid) == 0);
|
|
}
|
|
|
|
/* OK, now we have the following:
|
|
higuy < loguy
|
|
lo <= higuy <= hi
|
|
A[i] <= A[mid] for lo <= i <= higuy
|
|
A[i] == A[mid] for higuy < i < loguy
|
|
A[i] > A[mid] for loguy <= i < hi
|
|
A[hi] >= A[mid] */
|
|
|
|
/* We've finished the partition, now we want to sort the subarrays
|
|
[lo, higuy] and [loguy, hi].
|
|
We do the smaller one first to minimize stack usage.
|
|
We only sort arrays of length 2 or more.*/
|
|
|
|
if ( higuy - lo >= hi - loguy ) {
|
|
if (lo < higuy) {
|
|
lostk[stkptr] = lo;
|
|
histk[stkptr] = higuy;
|
|
++stkptr;
|
|
} /* save big recursion for later */
|
|
|
|
if (loguy < hi) {
|
|
lo = loguy;
|
|
goto recurse; /* do small recursion */
|
|
}
|
|
}
|
|
else {
|
|
if (loguy < hi) {
|
|
lostk[stkptr] = loguy;
|
|
histk[stkptr] = hi;
|
|
++stkptr; /* save big recursion for later */
|
|
}
|
|
|
|
if (lo < higuy) {
|
|
hi = higuy;
|
|
goto recurse; /* do small recursion */
|
|
}
|
|
}
|
|
}
|
|
|
|
/* We have sorted the array, except for any pending sorts on the stack.
|
|
Check if there are any, and do them. */
|
|
|
|
--stkptr;
|
|
if (stkptr >= 0) {
|
|
lo = lostk[stkptr];
|
|
hi = histk[stkptr];
|
|
goto recurse; /* pop subarray from stack */
|
|
}
|
|
else
|
|
return; /* all subarrays done */
|
|
}
|
|
|
|
|
|
/***
|
|
*shortsort(hi, lo, width, comp) - insertion sort for sorting short arrays
|
|
*
|
|
*Purpose:
|
|
* sorts the sub-array of elements between lo and hi (inclusive)
|
|
* side effects: sorts in place
|
|
* assumes that lo < hi
|
|
*
|
|
*Entry:
|
|
* char *lo = pointer to low element to sort
|
|
* char *hi = pointer to high element to sort
|
|
* size_t width = width in bytes of each array element
|
|
* int (*comp)() = pointer to function returning analog of strcmp for
|
|
* strings, but supplied by user for comparing the array elements.
|
|
* it accepts 2 pointers to elements and returns neg if 1<2, 0 if
|
|
* 1=2, pos if 1>2.
|
|
*
|
|
*Exit:
|
|
* returns void
|
|
*
|
|
*Exceptions:
|
|
*
|
|
*******************************************************************************/
|
|
|
|
static void __cdecl shortsort (
|
|
char *lo,
|
|
char *hi,
|
|
size_t width,
|
|
int (__cdecl *comp)(const void *, const void *)
|
|
)
|
|
{
|
|
char *p, *max;
|
|
|
|
/* Note: in assertions below, i and j are alway inside original bound of
|
|
array to sort. */
|
|
|
|
while (hi > lo) {
|
|
/* A[i] <= A[j] for i <= j, j > hi */
|
|
max = lo;
|
|
for (p = lo+width; p <= hi; p += width) {
|
|
/* A[i] <= A[max] for lo <= i < p */
|
|
if (comp(p, max) > 0) {
|
|
max = p;
|
|
}
|
|
/* A[i] <= A[max] for lo <= i <= p */
|
|
}
|
|
|
|
/* A[i] <= A[max] for lo <= i <= hi */
|
|
|
|
swap(max, hi, width);
|
|
|
|
/* A[i] <= A[hi] for i <= hi, so A[i] <= A[j] for i <= j, j >= hi */
|
|
|
|
hi -= width;
|
|
|
|
/* A[i] <= A[j] for i <= j, j > hi, loop top condition established */
|
|
}
|
|
/* A[i] <= A[j] for i <= j, j > lo, which implies A[i] <= A[j] for i < j,
|
|
so array is sorted */
|
|
}
|
|
|
|
|
|
/***
|
|
*swap(a, b, width) - swap two elements
|
|
*
|
|
*Purpose:
|
|
* swaps the two array elements of size width
|
|
*
|
|
*Entry:
|
|
* char *a, *b = pointer to two elements to swap
|
|
* size_t width = width in bytes of each array element
|
|
*
|
|
*Exit:
|
|
* returns void
|
|
*
|
|
*Exceptions:
|
|
*
|
|
*******************************************************************************/
|
|
|
|
static void __cdecl swap (
|
|
char *a,
|
|
char *b,
|
|
size_t width
|
|
)
|
|
{
|
|
char tmp;
|
|
|
|
if ( a != b )
|
|
/* Do the swap one character at a time to avoid potential alignment
|
|
problems. */
|
|
while ( width-- ) {
|
|
tmp = *a;
|
|
*a++ = *b;
|
|
*b++ = tmp;
|
|
}
|
|
}
|