src/stdlib/SDL_qsort.c - external/github.com/libsdl-org/SDL - Git at Google

 /* qsort.c
  * (c) 1998 Gareth McCaughan
  *
  * This is a drop-in replacement for the C library's |qsort()| routine.
  *
  * Features:
  *   - Median-of-three pivoting (and more)
  *   - Truncation and final polishing by a single insertion sort
  *   - Early truncation when no swaps needed in pivoting step
  *   - Explicit recursion, guaranteed not to overflow
  *   - A few little wrinkles stolen from the GNU |qsort()|.
  *   - separate code for non-aligned / aligned / word-size objects
  *
  * This code may be reproduced freely provided
  *   - this file is retained unaltered apart from minor
  *     changes for portability and efficiency
  *   - no changes are made to this comment
  *   - any changes that *are* made are clearly flagged
  *   - the _ID string below is altered by inserting, after
  *     the date, the string " altered" followed at your option
  *     by other material. (Exceptions: you may change the name
  *     of the exported routine without changing the ID string.
  *     You may change the values of the macros TRUNC_* and
  *     PIVOT_THRESHOLD without changing the ID string, provided
  *     they remain constants with TRUNC_nonaligned, TRUNC_aligned
  *     and TRUNC_words/WORD_BYTES between 8 and 24, and
  *     PIVOT_THRESHOLD between 32 and 200.)
  *
  * You may use it in anything you like; you may make money
  * out of it; you may distribute it in object form or as
  * part of an executable without including source code;
  * you don't have to credit me. (But it would be nice if
  * you did.)
  *
  * If you find problems with this code, or find ways of
  * making it significantly faster, please let me know!
  * My e-mail address, valid as of early 1998 and certainly
  * OK for at least the next 18 months, is
  *    gjm11@dpmms.cam.ac.uk
  * Thanks!
  *
  * Gareth McCaughan   Peterhouse   Cambridge   1998
  */
 #include "SDL_config.h"

 /*
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 */
 #include "SDL_stdinc.h"
 #include "SDL_assert.h"

 #if defined(HAVE_QSORT)
 void
 SDL_qsort(void *base, size_t nmemb, size_t size, int (*compare) (const void *, const void *))
 {
     qsort(base, nmemb, size, compare);
 }
 #else

 #ifdef assert
 #undef assert
 #endif
 #define assert(X) SDL_assert(X)
 #ifdef malloc
 #undef malloc
 #endif
 #define malloc	SDL_malloc
 #ifdef free
 #undef free
 #endif
 #define free	SDL_free
 #ifdef memcpy
 #undef memcpy
 #endif
 #define memcpy	SDL_memcpy
 #ifdef memmove
 #undef memmove
 #endif
 #define memmove	SDL_memmove
 #ifdef qsort
 #undef qsort
 #endif
 #define qsort	SDL_qsort

 static const char _ID[] = "<qsort.c gjm 1.12 1998-03-19>";

 /* How many bytes are there per word? (Must be a power of 2,
  * and must in fact equal sizeof(int).)
  */
 #define WORD_BYTES sizeof(int)

 /* How big does our stack need to be? Answer: one entry per
  * bit in a |size_t|.
  */
 #define STACK_SIZE (8*sizeof(size_t))

 /* Different situations have slightly different requirements,
  * and we make life epsilon easier by using different truncation
  * points for the three different cases.
  * So far, I have tuned TRUNC_words and guessed that the same
  * value might work well for the other two cases. Of course
  * what works well on my machine might work badly on yours.
  */
 #define TRUNC_nonaligned	12
 #define TRUNC_aligned		12
 #define TRUNC_words		12*WORD_BYTES   /* nb different meaning */

 /* We use a simple pivoting algorithm for shortish sub-arrays
  * and a more complicated one for larger ones. The threshold
  * is PIVOT_THRESHOLD.
  */
 #define PIVOT_THRESHOLD 40

 typedef struct
 {
     char *first;
     char *last;
 } stack_entry;
 #define pushLeft {stack[stacktop].first=ffirst;stack[stacktop++].last=last;}
 #define pushRight {stack[stacktop].first=first;stack[stacktop++].last=llast;}
 #define doLeft {first=ffirst;llast=last;continue;}
 #define doRight {ffirst=first;last=llast;continue;}
 #define pop {if (--stacktop<0) break;\
   first=ffirst=stack[stacktop].first;\
   last=llast=stack[stacktop].last;\
   continue;}

 /* Some comments on the implementation.
  * 1. When we finish partitioning the array into "low"
  *    and "high", we forget entirely about short subarrays,
  *    because they'll be done later by insertion sort.
  *    Doing lots of little insertion sorts might be a win
  *    on large datasets for locality-of-reference reasons,
  *    but it makes the code much nastier and increases
  *    bookkeeping overhead.
  * 2. We always save the shorter and get to work on the
  *    longer. This guarantees that every time we push
  *    an item onto the stack its size is <= 1/2 of that
  *    of its parent; so the stack can't need more than
  *    log_2(max-array-size) entries.
  * 3. We choose a pivot by looking at the first, last
  *    and middle elements. We arrange them into order
  *    because it's easy to do that in conjunction with
  *    choosing the pivot, and it makes things a little
  *    easier in the partitioning step. Anyway, the pivot
  *    is the middle of these three. It's still possible
  *    to construct datasets where the algorithm takes
  *    time of order n^2, but it simply never happens in
  *    practice.
  * 3' Newsflash: On further investigation I find that
  *    it's easy to construct datasets where median-of-3
  *    simply isn't good enough. So on large-ish subarrays
  *    we do a more sophisticated pivoting: we take three
  *    sets of 3 elements, find their medians, and then
  *    take the median of those.
  * 4. We copy the pivot element to a separate place
  *    because that way we can always do our comparisons
  *    directly against a pointer to that separate place,
  *    and don't have to wonder "did we move the pivot
  *    element?". This makes the inner loop better.
  * 5. It's possible to make the pivoting even more
  *    reliable by looking at more candidates when n
  *    is larger. (Taking this to its logical conclusion
  *    results in a variant of quicksort that doesn't
  *    have that n^2 worst case.) However, the overhead
  *    from the extra bookkeeping means that it's just
  *    not worth while.
  * 6. This is pretty clean and portable code. Here are
  *    all the potential portability pitfalls and problems
  *    I know of:
  *      - In one place (the insertion sort) I construct
  *        a pointer that points just past the end of the
  *        supplied array, and assume that (a) it won't
  *        compare equal to any pointer within the array,
  *        and (b) it will compare equal to a pointer
  *        obtained by stepping off the end of the array.
  *        These might fail on some segmented architectures.
  *      - I assume that there are 8 bits in a |char| when
  *        computing the size of stack needed. This would
  *        fail on machines with 9-bit or 16-bit bytes.
  *      - I assume that if |((int)base&(sizeof(int)-1))==0|
  *        and |(size&(sizeof(int)-1))==0| then it's safe to
  *        get at array elements via |int*|s, and that if
  *        actually |size==sizeof(int)| as well then it's
  *        safe to treat the elements as |int|s. This might
  *        fail on systems that convert pointers to integers
  *        in non-standard ways.
  *      - I assume that |8*sizeof(size_t)<=INT_MAX|. This
  *        would be false on a machine with 8-bit |char|s,
  *        16-bit |int|s and 4096-bit |size_t|s. :-)
  */

 /* The recursion logic is the same in each case: */
 #define Recurse(Trunc)				\
       { size_t l=last-ffirst,r=llast-first;	\
         if (l<Trunc) {				\
           if (r>=Trunc) doRight			\
           else pop				\
         }					\
         else if (l<=r) { pushLeft; doRight }	\
         else if (r>=Trunc) { pushRight; doLeft }\
         else doLeft				\
       }

 /* and so is the pivoting logic: */
 #define Pivot(swapper,sz)			\
   if ((size_t)(last-first)>PIVOT_THRESHOLD*sz) mid=pivot_big(first,mid,last,sz,compare);\
   else {	\
     if (compare(first,mid)<0) {			\
       if (compare(mid,last)>0) {		\
         swapper(mid,last);			\
         if (compare(first,mid)>0) swapper(first,mid);\
       }						\
     }						\
     else {					\
       if (compare(mid,last)>0) swapper(first,last)\
       else {					\
         swapper(first,mid);			\
         if (compare(mid,last)>0) swapper(mid,last);\
       }						\
     }						\
     first+=sz; last-=sz;			\
   }

 #ifdef DEBUG_QSORT
 #include <stdio.h>
 #endif

 /* and so is the partitioning logic: */
 #define Partition(swapper,sz) {			\
   int swapped=0;				\
   do {						\
     while (compare(first,pivot)<0) first+=sz;	\
     while (compare(pivot,last)<0) last-=sz;	\
     if (first<last) {				\
       swapper(first,last); swapped=1;		\
       first+=sz; last-=sz; }			\
     else if (first==last) { first+=sz; last-=sz; break; }\
   } while (first<=last);			\
   if (!swapped) pop				\
 }

 /* and so is the pre-insertion-sort operation of putting
  * the smallest element into place as a sentinel.
  * Doing this makes the inner loop nicer. I got this
  * idea from the GNU implementation of qsort().
  */
 #define PreInsertion(swapper,limit,sz)		\
   first=base;					\
   last=first + (nmemb>limit ? limit : nmemb-1)*sz;\
   while (last!=base) {				\
     if (compare(first,last)>0) first=last;	\
     last-=sz; }					\
   if (first!=base) swapper(first,(char*)base);

 /* and so is the insertion sort, in the first two cases: */
 #define Insertion(swapper)			\
   last=((char*)base)+nmemb*size;		\
   for (first=((char*)base)+size;first!=last;first+=size) {	\
     char *test;					\
     /* Find the right place for |first|.	\
      * My apologies for var reuse. */		\
     for (test=first-size;compare(test,first)>0;test-=size) ;	\
     test+=size;					\
     if (test!=first) {				\
       /* Shift everything in [test,first)	\
        * up by one, and place |first|		\
        * where |test| is. */			\
       memcpy(pivot,first,size);			\
       memmove(test+size,test,first-test);	\
       memcpy(test,pivot,size);			\
     }						\
   }

 #define SWAP_nonaligned(a,b) { \
   register char *aa=(a),*bb=(b); \
   register size_t sz=size; \
   do { register char t=*aa; *aa++=*bb; *bb++=t; } while (--sz); }

 #define SWAP_aligned(a,b) { \
   register int *aa=(int*)(a),*bb=(int*)(b); \
   register size_t sz=size; \
   do { register int t=*aa;*aa++=*bb; *bb++=t; } while (sz-=WORD_BYTES); }

 #define SWAP_words(a,b) { \
   register int t=*((int*)a); *((int*)a)=*((int*)b); *((int*)b)=t; }

 /* ---------------------------------------------------------------------- */

 static char *
 pivot_big(char *first, char *mid, char *last, size_t size,
           int compare(const void *, const void *))
 {
     size_t d = (((last - first) / size) >> 3) * size;
     char *m1, *m2, *m3;
     {
         char *a = first, *b = first + d, *c = first + 2 * d;
 #ifdef DEBUG_QSORT
         fprintf(stderr, "< %d %d %d\n", *(int *) a, *(int *) b, *(int *) c);
 #endif
         m1 = compare(a, b) < 0 ?
             (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
             : (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
     }
     {
         char *a = mid - d, *b = mid, *c = mid + d;
 #ifdef DEBUG_QSORT
         fprintf(stderr, ". %d %d %d\n", *(int *) a, *(int *) b, *(int *) c);
 #endif
         m2 = compare(a, b) < 0 ?
             (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
             : (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
     }
     {
         char *a = last - 2 * d, *b = last - d, *c = last;
 #ifdef DEBUG_QSORT
         fprintf(stderr, "> %d %d %d\n", *(int *) a, *(int *) b, *(int *) c);
 #endif
         m3 = compare(a, b) < 0 ?
             (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
             : (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
     }
 #ifdef DEBUG_QSORT
     fprintf(stderr, "-> %d %d %d\n", *(int *) m1, *(int *) m2, *(int *) m3);
 #endif
     return compare(m1, m2) < 0 ?
         (compare(m2, m3) < 0 ? m2 : (compare(m1, m3) < 0 ? m3 : m1))
         : (compare(m1, m3) < 0 ? m1 : (compare(m2, m3) < 0 ? m3 : m2));
 }

 /* ---------------------------------------------------------------------- */

 static void
 qsort_nonaligned(void *base, size_t nmemb, size_t size,
                  int (*compare) (const void *, const void *))
 {

     stack_entry stack[STACK_SIZE];
     int stacktop = 0;
     char *first, *last;
     char *pivot = malloc(size);
     size_t trunc = TRUNC_nonaligned * size;
     assert(pivot != 0);

     first = (char *) base;
     last = first + (nmemb - 1) * size;

     if ((size_t) (last - first) > trunc) {
         char *ffirst = first, *llast = last;
         while (1) {
             /* Select pivot */
             {
                 char *mid = first + size * ((last - first) / size >> 1);
                 Pivot(SWAP_nonaligned, size);
                 memcpy(pivot, mid, size);
             }
             /* Partition. */
             Partition(SWAP_nonaligned, size);
             /* Prepare to recurse/iterate. */
         Recurse(trunc)}
     }
     PreInsertion(SWAP_nonaligned, TRUNC_nonaligned, size);
     Insertion(SWAP_nonaligned);
     free(pivot);
 }

 static void
 qsort_aligned(void *base, size_t nmemb, size_t size,
               int (*compare) (const void *, const void *))
 {

     stack_entry stack[STACK_SIZE];
     int stacktop = 0;
     char *first, *last;
     char *pivot = malloc(size);
     size_t trunc = TRUNC_aligned * size;
     assert(pivot != 0);

     first = (char *) base;
     last = first + (nmemb - 1) * size;

     if ((size_t) (last - first) > trunc) {
         char *ffirst = first, *llast = last;
         while (1) {
             /* Select pivot */
             {
                 char *mid = first + size * ((last - first) / size >> 1);
                 Pivot(SWAP_aligned, size);
                 memcpy(pivot, mid, size);
             }
             /* Partition. */
             Partition(SWAP_aligned, size);
             /* Prepare to recurse/iterate. */
         Recurse(trunc)}
     }
     PreInsertion(SWAP_aligned, TRUNC_aligned, size);
     Insertion(SWAP_aligned);
     free(pivot);
 }

 static void
 qsort_words(void *base, size_t nmemb,
             int (*compare) (const void *, const void *))
 {

     stack_entry stack[STACK_SIZE];
     int stacktop = 0;
     char *first, *last;
     char *pivot = malloc(WORD_BYTES);
     assert(pivot != 0);

     first = (char *) base;
     last = first + (nmemb - 1) * WORD_BYTES;

     if (last - first > TRUNC_words) {
         char *ffirst = first, *llast = last;
         while (1) {
 #ifdef DEBUG_QSORT
             fprintf(stderr, "Doing %d:%d: ",
                     (first - (char *) base) / WORD_BYTES,
                     (last - (char *) base) / WORD_BYTES);
 #endif
             /* Select pivot */
             {
                 char *mid =
                     first + WORD_BYTES * ((last - first) / (2 * WORD_BYTES));
                 Pivot(SWAP_words, WORD_BYTES);
                 *(int *) pivot = *(int *) mid;
             }
 #ifdef DEBUG_QSORT
             fprintf(stderr, "pivot=%d\n", *(int *) pivot);
 #endif
             /* Partition. */
             Partition(SWAP_words, WORD_BYTES);
             /* Prepare to recurse/iterate. */
         Recurse(TRUNC_words)}
     }
     PreInsertion(SWAP_words, (TRUNC_words / WORD_BYTES), WORD_BYTES);
     /* Now do insertion sort. */
     last = ((char *) base) + nmemb * WORD_BYTES;
     for (first = ((char *) base) + WORD_BYTES; first != last;
          first += WORD_BYTES) {
         /* Find the right place for |first|. My apologies for var reuse */
         int *pl = (int *) (first - WORD_BYTES), *pr = (int *) first;
         *(int *) pivot = *(int *) first;
         for (; compare(pl, pivot) > 0; pr = pl, --pl) {
             *pr = *pl;
         }
         if (pr != (int *) first)
             *pr = *(int *) pivot;
     }
     free(pivot);
 }

 /* ---------------------------------------------------------------------- */

 void
 qsort(void *base, size_t nmemb, size_t size,
       int (*compare) (const void *, const void *))
 {

     if (nmemb <= 1)
         return;
     if (((uintptr_t) base | size) & (WORD_BYTES - 1))
         qsort_nonaligned(base, nmemb, size, compare);
     else if (size != WORD_BYTES)
         qsort_aligned(base, nmemb, size, compare);
     else
         qsort_words(base, nmemb, compare);
 }

 #endif /* !SDL_qsort */

 /* vi: set ts=4 sw=4 expandtab: */
	/* qsort.c
	* (c) 1998 Gareth McCaughan
	*
	* This is a drop-in replacement for the C library's \|qsort()\| routine.
	*
	* Features:
	* - Median-of-three pivoting (and more)
	* - Truncation and final polishing by a single insertion sort
	* - Early truncation when no swaps needed in pivoting step
	* - Explicit recursion, guaranteed not to overflow
	* - A few little wrinkles stolen from the GNU \|qsort()\|.
	* - separate code for non-aligned / aligned / word-size objects
	*
	* This code may be reproduced freely provided
	* - this file is retained unaltered apart from minor
	* changes for portability and efficiency
	* - no changes are made to this comment
	* - any changes that are made are clearly flagged
	* - the _ID string below is altered by inserting, after
	* the date, the string " altered" followed at your option
	* by other material. (Exceptions: you may change the name
	* of the exported routine without changing the ID string.
	* You may change the values of the macros TRUNC_* and
	* PIVOT_THRESHOLD without changing the ID string, provided
	* they remain constants with TRUNC_nonaligned, TRUNC_aligned
	* and TRUNC_words/WORD_BYTES between 8 and 24, and
	* PIVOT_THRESHOLD between 32 and 200.)
	*
	* You may use it in anything you like; you may make money
	* out of it; you may distribute it in object form or as
	* part of an executable without including source code;
	* you don't have to credit me. (But it would be nice if
	* you did.)
	*
	* If you find problems with this code, or find ways of
	* making it significantly faster, please let me know!
	* My e-mail address, valid as of early 1998 and certainly
	* OK for at least the next 18 months, is
	* gjm11@dpmms.cam.ac.uk
	* Thanks!
	*
	* Gareth McCaughan Peterhouse Cambridge 1998
	*/
	#include "SDL_config.h"

	/*
	#include <assert.h>
	#include <stdlib.h>
	#include <string.h>
	*/
	#include "SDL_stdinc.h"
	#include "SDL_assert.h"

	#if defined(HAVE_QSORT)
	void
	SDL_qsort(void base, size_t nmemb, size_t size, int (compare) (const void , const void ))
	{
	qsort(base, nmemb, size, compare);
	}
	#else

	#ifdef assert
	#undef assert
	#endif
	#define assert(X) SDL_assert(X)
	#ifdef malloc
	#undef malloc
	#endif
	#define malloc SDL_malloc
	#ifdef free
	#undef free
	#endif
	#define free SDL_free
	#ifdef memcpy
	#undef memcpy
	#endif
	#define memcpy SDL_memcpy
	#ifdef memmove
	#undef memmove
	#endif
	#define memmove SDL_memmove
	#ifdef qsort
	#undef qsort
	#endif
	#define qsort SDL_qsort

	static const char _ID[] = "<qsort.c gjm 1.12 1998-03-19>";

	/* How many bytes are there per word? (Must be a power of 2,
	* and must in fact equal sizeof(int).)
	*/
	#define WORD_BYTES sizeof(int)

	/* How big does our stack need to be? Answer: one entry per
	* bit in a \|size_t\|.
	*/
	#define STACK_SIZE (8*sizeof(size_t))

	/* Different situations have slightly different requirements,
	* and we make life epsilon easier by using different truncation
	* points for the three different cases.
	* So far, I have tuned TRUNC_words and guessed that the same
	* value might work well for the other two cases. Of course
	* what works well on my machine might work badly on yours.
	*/
	#define TRUNC_nonaligned 12
	#define TRUNC_aligned 12
	#define TRUNC_words 12WORD_BYTES / nb different meaning */

	/* We use a simple pivoting algorithm for shortish sub-arrays
	* and a more complicated one for larger ones. The threshold
	* is PIVOT_THRESHOLD.
	*/
	#define PIVOT_THRESHOLD 40

	typedef struct
	{
	char *first;
	char *last;
	} stack_entry;
	#define pushLeft {stack[stacktop].first=ffirst;stack[stacktop++].last=last;}
	#define pushRight {stack[stacktop].first=first;stack[stacktop++].last=llast;}
	#define doLeft {first=ffirst;llast=last;continue;}
	#define doRight {ffirst=first;last=llast;continue;}
	#define pop {if (--stacktop<0) break;\
	first=ffirst=stack[stacktop].first;\
	last=llast=stack[stacktop].last;\
	continue;}

	/* Some comments on the implementation.
	* 1. When we finish partitioning the array into "low"
	* and "high", we forget entirely about short subarrays,
	* because they'll be done later by insertion sort.
	* Doing lots of little insertion sorts might be a win
	* on large datasets for locality-of-reference reasons,
	* but it makes the code much nastier and increases
	* bookkeeping overhead.
	* 2. We always save the shorter and get to work on the
	* longer. This guarantees that every time we push
	* an item onto the stack its size is <= 1/2 of that
	* of its parent; so the stack can't need more than
	* log_2(max-array-size) entries.
	* 3. We choose a pivot by looking at the first, last
	* and middle elements. We arrange them into order
	* because it's easy to do that in conjunction with
	* choosing the pivot, and it makes things a little
	* easier in the partitioning step. Anyway, the pivot
	* is the middle of these three. It's still possible
	* to construct datasets where the algorithm takes
	* time of order n^2, but it simply never happens in
	* practice.
	* 3' Newsflash: On further investigation I find that
	* it's easy to construct datasets where median-of-3
	* simply isn't good enough. So on large-ish subarrays
	* we do a more sophisticated pivoting: we take three
	* sets of 3 elements, find their medians, and then
	* take the median of those.
	* 4. We copy the pivot element to a separate place
	* because that way we can always do our comparisons
	* directly against a pointer to that separate place,
	* and don't have to wonder "did we move the pivot
	* element?". This makes the inner loop better.
	* 5. It's possible to make the pivoting even more
	* reliable by looking at more candidates when n
	* is larger. (Taking this to its logical conclusion
	* results in a variant of quicksort that doesn't
	* have that n^2 worst case.) However, the overhead
	* from the extra bookkeeping means that it's just
	* not worth while.
	* 6. This is pretty clean and portable code. Here are
	* all the potential portability pitfalls and problems
	* I know of:
	* - In one place (the insertion sort) I construct
	* a pointer that points just past the end of the
	* supplied array, and assume that (a) it won't
	* compare equal to any pointer within the array,
	* and (b) it will compare equal to a pointer
	* obtained by stepping off the end of the array.
	* These might fail on some segmented architectures.
	* - I assume that there are 8 bits in a \|char\| when
	* computing the size of stack needed. This would
	* fail on machines with 9-bit or 16-bit bytes.
	* - I assume that if \|((int)base&(sizeof(int)-1))==0\|
	* and \|(size&(sizeof(int)-1))==0\| then it's safe to
	* get at array elements via \|int*\|s, and that if
	* actually \|size==sizeof(int)\| as well then it's
	* safe to treat the elements as \|int\|s. This might
	* fail on systems that convert pointers to integers
	* in non-standard ways.
	* - I assume that \|8*sizeof(size_t)<=INT_MAX\|. This
	* would be false on a machine with 8-bit \|char\|s,
	* 16-bit \|int\|s and 4096-bit \|size_t\|s. :-)
	*/

	/* The recursion logic is the same in each case: */
	#define Recurse(Trunc) \
	{ size_t l=last-ffirst,r=llast-first; \
	if (l<Trunc) { \
	if (r>=Trunc) doRight \
	else pop \
	} \
	else if (l<=r) { pushLeft; doRight } \
	else if (r>=Trunc) { pushRight; doLeft }\
	else doLeft \
	}

	/* and so is the pivoting logic: */
	#define Pivot(swapper,sz) \
	if ((size_t)(last-first)>PIVOT_THRESHOLD*sz) mid=pivot_big(first,mid,last,sz,compare);\
	else { \
	if (compare(first,mid)<0) { \
	if (compare(mid,last)>0) { \
	swapper(mid,last); \
	if (compare(first,mid)>0) swapper(first,mid);\
	} \
	} \
	else { \
	if (compare(mid,last)>0) swapper(first,last)\
	else { \
	swapper(first,mid); \
	if (compare(mid,last)>0) swapper(mid,last);\
	} \
	} \
	first+=sz; last-=sz; \
	}

	#ifdef DEBUG_QSORT
	#include <stdio.h>
	#endif

	/* and so is the partitioning logic: */
	#define Partition(swapper,sz) { \
	int swapped=0; \
	do { \
	while (compare(first,pivot)<0) first+=sz; \
	while (compare(pivot,last)<0) last-=sz; \
	if (first<last) { \
	swapper(first,last); swapped=1; \
	first+=sz; last-=sz; } \
	else if (first==last) { first+=sz; last-=sz; break; }\
	} while (first<=last); \
	if (!swapped) pop \
	}

	/* and so is the pre-insertion-sort operation of putting
	* the smallest element into place as a sentinel.
	* Doing this makes the inner loop nicer. I got this
	* idea from the GNU implementation of qsort().
	*/
	#define PreInsertion(swapper,limit,sz) \
	first=base; \
	last=first + (nmemb>limit ? limit : nmemb-1)*sz;\
	while (last!=base) { \
	if (compare(first,last)>0) first=last; \
	last-=sz; } \
	if (first!=base) swapper(first,(char*)base);

	/* and so is the insertion sort, in the first two cases: */
	#define Insertion(swapper) \
	last=((char)base)+nmembsize; \
	for (first=((char*)base)+size;first!=last;first+=size) { \
	char *test; \
	/* Find the right place for \|first\|. \
	* My apologies for var reuse. */ \
	for (test=first-size;compare(test,first)>0;test-=size) ; \
	test+=size; \
	if (test!=first) { \
	/* Shift everything in [test,first) \
	* up by one, and place \|first\| \
	* where \|test\| is. */ \
	memcpy(pivot,first,size); \
	memmove(test+size,test,first-test); \
	memcpy(test,pivot,size); \
	} \
	}

	#define SWAP_nonaligned(a,b) { \
	register char aa=(a),bb=(b); \
	register size_t sz=size; \
	do { register char t=aa; aa++=bb; bb++=t; } while (--sz); }

	#define SWAP_aligned(a,b) { \
	register int aa=(int)(a),bb=(int)(b); \
	register size_t sz=size; \
	do { register int t=aa;aa++=bb; bb++=t; } while (sz-=WORD_BYTES); }

	#define SWAP_words(a,b) { \
	register int t=((int)a); ((int)a)=((int)b); ((int)b)=t; }

	/* ---------------------------------------------------------------------- */

	static char *
	pivot_big(char first, char mid, char *last, size_t size,
	int compare(const void , const void ))
	{
	size_t d = (((last - first) / size) >> 3) * size;
	char m1, m2, *m3;
	{
	char a = first, b = first + d, c = first + 2 d;
	#ifdef DEBUG_QSORT
	fprintf(stderr, "< %d %d %d\n", (int ) a, (int ) b, (int ) c);
	#endif
	m1 = compare(a, b) < 0 ?
	(compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
	: (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
	}
	{
	char a = mid - d, b = mid, *c = mid + d;
	#ifdef DEBUG_QSORT
	fprintf(stderr, ". %d %d %d\n", (int ) a, (int ) b, (int ) c);
	#endif
	m2 = compare(a, b) < 0 ?
	(compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
	: (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
	}
	{
	char a = last - 2 d, b = last - d, c = last;
	#ifdef DEBUG_QSORT
	fprintf(stderr, "> %d %d %d\n", (int ) a, (int ) b, (int ) c);
	#endif
	m3 = compare(a, b) < 0 ?
	(compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
	: (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
	}
	#ifdef DEBUG_QSORT
	fprintf(stderr, "-> %d %d %d\n", (int ) m1, (int ) m2, (int ) m3);
	#endif
	return compare(m1, m2) < 0 ?
	(compare(m2, m3) < 0 ? m2 : (compare(m1, m3) < 0 ? m3 : m1))
	: (compare(m1, m3) < 0 ? m1 : (compare(m2, m3) < 0 ? m3 : m2));
	}

	/* ---------------------------------------------------------------------- */

	static void
	qsort_nonaligned(void *base, size_t nmemb, size_t size,
	int (compare) (const void , const void *))
	{

	stack_entry stack[STACK_SIZE];
	int stacktop = 0;
	char first, last;
	char *pivot = malloc(size);
	size_t trunc = TRUNC_nonaligned * size;
	assert(pivot != 0);

	first = (char *) base;
	last = first + (nmemb - 1) * size;

	if ((size_t) (last - first) > trunc) {
	char ffirst = first, llast = last;
	while (1) {
	/* Select pivot */
	{
	char mid = first + size ((last - first) / size >> 1);
	Pivot(SWAP_nonaligned, size);
	memcpy(pivot, mid, size);
	}
	/* Partition. */
	Partition(SWAP_nonaligned, size);
	/* Prepare to recurse/iterate. */
	Recurse(trunc)}
	}
	PreInsertion(SWAP_nonaligned, TRUNC_nonaligned, size);
	Insertion(SWAP_nonaligned);
	free(pivot);
	}

	static void
	qsort_aligned(void *base, size_t nmemb, size_t size,
	int (compare) (const void , const void *))
	{

	stack_entry stack[STACK_SIZE];
	int stacktop = 0;
	char first, last;
	char *pivot = malloc(size);
	size_t trunc = TRUNC_aligned * size;
	assert(pivot != 0);

	first = (char *) base;
	last = first + (nmemb - 1) * size;

	if ((size_t) (last - first) > trunc) {
	char ffirst = first, llast = last;
	while (1) {
	/* Select pivot */
	{
	char mid = first + size ((last - first) / size >> 1);
	Pivot(SWAP_aligned, size);
	memcpy(pivot, mid, size);
	}
	/* Partition. */
	Partition(SWAP_aligned, size);
	/* Prepare to recurse/iterate. */
	Recurse(trunc)}
	}
	PreInsertion(SWAP_aligned, TRUNC_aligned, size);
	Insertion(SWAP_aligned);
	free(pivot);
	}

	static void
	qsort_words(void *base, size_t nmemb,
	int (compare) (const void , const void *))
	{

	stack_entry stack[STACK_SIZE];
	int stacktop = 0;
	char first, last;
	char *pivot = malloc(WORD_BYTES);
	assert(pivot != 0);

	first = (char *) base;
	last = first + (nmemb - 1) * WORD_BYTES;

	if (last - first > TRUNC_words) {
	char ffirst = first, llast = last;
	while (1) {
	#ifdef DEBUG_QSORT
	fprintf(stderr, "Doing %d:%d: ",
	(first - (char *) base) / WORD_BYTES,
	(last - (char *) base) / WORD_BYTES);
	#endif
	/* Select pivot */
	{
	char *mid =
	first + WORD_BYTES * ((last - first) / (2 * WORD_BYTES));
	Pivot(SWAP_words, WORD_BYTES);
	(int ) pivot = (int ) mid;
	}
	#ifdef DEBUG_QSORT
	fprintf(stderr, "pivot=%d\n", (int ) pivot);
	#endif
	/* Partition. */
	Partition(SWAP_words, WORD_BYTES);
	/* Prepare to recurse/iterate. */
	Recurse(TRUNC_words)}
	}
	PreInsertion(SWAP_words, (TRUNC_words / WORD_BYTES), WORD_BYTES);
	/* Now do insertion sort. */
	last = ((char ) base) + nmemb WORD_BYTES;
	for (first = ((char *) base) + WORD_BYTES; first != last;
	first += WORD_BYTES) {
	/* Find the right place for \|first\|. My apologies for var reuse */
	int pl = (int ) (first - WORD_BYTES), pr = (int ) first;
	(int ) pivot = (int ) first;
	for (; compare(pl, pivot) > 0; pr = pl, --pl) {
	pr = pl;
	}
	if (pr != (int *) first)
	pr = (int *) pivot;
	}
	free(pivot);
	}

	/* ---------------------------------------------------------------------- */

	void
	qsort(void *base, size_t nmemb, size_t size,
	int (compare) (const void , const void *))
	{

	if (nmemb <= 1)
	return;
	if (((uintptr_t) base \| size) & (WORD_BYTES - 1))
	qsort_nonaligned(base, nmemb, size, compare);
	else if (size != WORD_BYTES)
	qsort_aligned(base, nmemb, size, compare);
	else
	qsort_words(base, nmemb, compare);
	}

	#endif /* !SDL_qsort */

	/* vi: set ts=4 sw=4 expandtab: */