stdlib: Restored previous qsort() implementation; the licensing is resolved.
authorRyan C. Gordon <icculus@icculus.org>
Sun, 21 Feb 2016 13:07:14 -0500
changeset 10085 a8e53dc3c5a1
parent 10084 3bd08d2d45b0
child 10087 96f7be2c885b
stdlib: Restored previous qsort() implementation; the licensing is resolved. Thanks to Gareth McCaughan for changing his code to the zlib license on our behalf!
src/stdlib/SDL_qsort.c
--- a/src/stdlib/SDL_qsort.c	Sat Feb 20 01:03:39 2016 -0500
+++ b/src/stdlib/SDL_qsort.c	Sun Feb 21 13:07:14 2016 -0500
@@ -1,3 +1,28 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+#if defined(__clang_analyzer__) && !defined(SDL_DISABLE_ANALYZE_MACROS)
+#define SDL_DISABLE_ANALYZE_MACROS 1
+#endif
+
 #include "../SDL_internal.h"
 
 #include "SDL_stdinc.h"
@@ -9,208 +34,501 @@
 {
     qsort(base, nmemb, size, compare);
 }
+
 #else
 
-#ifdef REGTEST
-#undef REGTEST
+#ifdef assert
+#undef assert
 #endif
-
-#ifdef TEST
-#undef TEST
+#define assert SDL_assert
+#ifdef malloc
+#undef malloc
 #endif
-
-#ifndef _PDCLIB_memswp
-#define _PDCLIB_memswp( i, j, size ) char tmp; do { tmp = *i; *i++ = *j; *j++ = tmp; } while ( --size );
+#define malloc SDL_malloc
+#ifdef free
+#undef free
 #endif
-
-#ifndef _PDCLIB_size_t
-#define _PDCLIB_size_t size_t
+#define free SDL_free
+#ifdef memcpy
+#undef memcpy
 #endif
-
-#ifdef qsort
-#undef qsort
+#define memcpy SDL_memcpy
+#ifdef memmove
+#undef memmove
 #endif
-#define qsort SDL_qsort
-
-#define inline SDL_INLINE
+#define memmove SDL_memmove
+#ifdef qsortG
+#undef qsortG
+#endif
+#define qsortG SDL_qsort
 
 /*
-This code came from PDCLib, under the public domain. Specifically this:
-https://bitbucket.org/pdclib/pdclib/raw/a82b02d0c7d4ed633b97f2a7639d9a10b1c92ec8/functions/stdlib/qsort.c
-The _PDCLIB_memswp macro was from
-https://bitbucket.org/pdclib/pdclib/src/a82b02d0c7d4ed633b97f2a7639d9a10b1c92ec8/platform/posix/internals/_PDCLIB_config.h?at=default&fileviewer=file-view-default#_PDCLIB_config.h-28
+This code came from Gareth McCaughan, under the zlib license.
+Specifically this: https://www.mccaughan.org.uk/software/qsort.c-1.14
 
-Everything below this comment until the HAVE_QSORT #endif was from PDCLib (minor changes noted inline).
+Everything below this comment until the HAVE_QSORT #endif was from Gareth
+(any minor changes will be noted inline).
+
+Thank you to Gareth for relicensing this code under the zlib license for our
+benefit!
+
 --ryan.
 */
 
-/* $Id$ */
-
-/* qsort( void *, size_t, size_t, int(*)( const void *, const void * ) )
+/* This is a drop-in replacement for the C library's |qsort()| routine.
+ *
+ * It is intended for use where you know or suspect that your
+ * platform's qsort is bad. If that isn't the case, then you
+ * should probably use the qsort your system gives you in preference
+ * to mine -- it will likely have been tested and tuned better.
+ *
+ * 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()|.
+ *     (For the avoidance of doubt, no code was stolen, only
+ *     broad ideas.)
+ *   - separate code for non-aligned / aligned / word-size objects
+ *
+ * Earlier releases of this code used an idiosyncratic licence
+ * I wrote myself, because I'm an idiot. The code is now released
+ * under the "zlib/libpng licence"; you will find the actual
+ * terms in the next comment. I request (but do not require)
+ * that if you make any changes beyond the name of the exported
+ * routine and reasonable tweaks to the TRUNC_* and
+ * PIVOT_THRESHOLD values, you modify the _ID string so as
+ * to make it clear that you have changed the code.
+ *
+ * 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 2016 and for the
+ * foreseeable future, is
+ *    gareth.mccaughan@pobox.com
+ * Thanks!
+ *
+ * Gareth McCaughan
+ */
 
-   This file is part of the Public Domain C Library (PDCLib).
-   Permission is granted to use, modify, and / or redistribute at will.
-*/
+/* Copyright (c) 1998-2016 Gareth McCaughan
+ *
+ * This software is provided 'as-is', without any express or implied
+ * warranty. In no event will the authors be held liable for any
+ * damages arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, subject to the following restrictions:
+ *
+ * 1. The origin of this software must not be misrepresented;
+ *    you must not claim that you wrote the original software.
+ *    If you use this software in a product, an acknowledgment
+ *    in the product documentation would be appreciated but
+ *    is not required.
+ *
+ * 2. Altered source versions must be plainly marked as such,
+ *    and must not be misrepresented as being the original software.
+ *
+ * 3. This notice may not be removed or altered from any source
+ *    distribution.
+ */
+
+/* Revision history since release:
+ *   1998-03-19 v1.12 First release I have any records of.
+ *   2007-09-02 v1.13 Fix bug kindly reported by Dan Bodoh
+ *                    (premature termination of recursion).
+ *                    Add a few clarifying comments.
+ *                    Minor improvements to debug output.
+ *   2016-02-21 v1.14 Replace licence with 2-clause BSD,
+ *                    and clarify a couple of things in
+ *                    comments. No code changes.
+ */
 
-/* I commented this out. --ryan. #include <stdlib.h> */
+/* BEGIN SDL CHANGE ... commented this out with an #if 0 block. --ryan. */
+#if 0
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define DEBUG_QSORT
+
+static char _ID[]="<qsort.c gjm 1.14 2016-02-21>";
+#endif
+/* END SDL CHANGE ... commented this out with an #if 0 block. --ryan. */
+
+/* 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)
 
-#ifndef REGTEST
+/* 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
 
-/* This implementation is taken from Paul Edward's PDPCLIB.
+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;}
 
-   Original code is credited to Raymond Gardner, Englewood CO.
-   Minor mods are credited to Paul Edwards.
-   Some reformatting and simplification done by Martin Baute.
-   All code is still Public Domain.
-*/
+/* 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. :-)
+ */
 
-/* Wrapper for _PDCLIB_memswp protects against multiple argument evaluation. */
-static inline void memswp( char * i, char * j, size_t size )
-{
-    _PDCLIB_memswp( i, j, size );
+/* The recursion logic is the same in each case.
+ * We keep chopping up until we reach subarrays of size
+ * strictly less than Trunc; we leave these unsorted. */
+#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 (note: last is inclusive): */
+#define Pivot(swapper,sz)			\
+  if (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) {			\
+  do {						\
+    while (compare(first,pivot)<0) first+=sz;	\
+    while (compare(pivot,last)<0) last-=sz;	\
+    if (first<last) {				\
+      swapper(first,last);			\
+      first+=sz; last-=sz; }			\
+    else if (first==last) { first+=sz; last-=sz; break; }\
+  } while (first<=last);			\
 }
 
-/* For small sets, insertion sort is faster than quicksort.
-   T is the threshold below which insertion sort will be used.
-   Must be 3 or larger.
-*/
-#define T 7
+/* 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().
+ * We find the smallest element from the first |nmemb|,
+ * or the first |limit|, whichever is smaller;
+ * therefore we must have ensured that the globally smallest
+ * element is in the first |limit|.
+ */
+#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);
 
-/* Macros for handling the QSort stack */
-#define PREPARE_STACK char * stack[STACKSIZE]; char * * stackptr = stack
-#define PUSH( base, limit ) stackptr[0] = base; stackptr[1] = limit; stackptr += 2
-#define POP( base, limit ) stackptr -= 2; base = stackptr[0]; limit = stackptr[1]
-/* TODO: Stack usage is log2( nmemb ) (minus what T shaves off the worst case).
-         Worst-case nmemb is platform dependent and should probably be 
-         configured through _PDCLIB_config.h.
-*/
-#define STACKSIZE 64
+/* 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);			\
+    }						\
+  }
 
-void qsort( void * base, size_t nmemb, size_t size, int (*compar)( const void *, const void * ) )
-{
-    char * i;
-    char * j;
-    _PDCLIB_size_t thresh = T * size;
-    char * base_          = (char *)base;
-    char * limit          = base_ + nmemb * size;
-    PREPARE_STACK;
+#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); }
 
-    for ( ;; )
-    {
-        if ( (size_t)( limit - base_ ) > thresh ) /* QSort for more than T elements. */
-        {
-            /* We work from second to last - first will be pivot element. */
-            i = base_ + size;
-            j = limit - size;
-            /* We swap first with middle element, then sort that with second
-               and last element so that eventually first element is the median
-               of the three - avoiding pathological pivots.
-               TODO: Instead of middle element, chose one randomly.
-            */
-            memswp( ( ( ( (size_t)( limit - base_ ) ) / size ) / 2 ) * size + base_, base_, size );
-            if ( compar( i, j ) > 0 ) memswp( i, j, size );
-            if ( compar( base_, j ) > 0 ) memswp( base_, j, size );
-            if ( compar( i, base_ ) > 0 ) memswp( i, base_, size );
-            /* Now we have the median for pivot element, entering main Quicksort. */
-            for ( ;; )
-            {
-                do
-                {
-                    /* move i right until *i >= pivot */
-                    i += size;
-                } while ( compar( i, base_ ) < 0 );
-                do
-                {
-                    /* move j left until *j <= pivot */
-                    j -= size;
-                } while ( compar( j, base_ ) > 0 );
-                if ( i > j )
-                {
-                    /* break loop if pointers crossed */
-                    break;
-                }
-                /* else swap elements, keep scanning */
-                memswp( i, j, size );
-            }
-            /* move pivot into correct place */
-            memswp( base_, j, size );
-            /* larger subfile base / limit to stack, sort smaller */
-            if ( j - base_ > limit - i )
-            {
-                /* left is larger */
-                PUSH( base_, j );
-                base_ = i;
-            }
-            else
-            {
-                /* right is larger */
-                PUSH( i, limit );
-                limit = j;
-            }
-        }
-        else /* insertion sort for less than T elements              */
-        {
-            for ( j = base_, i = j + size; i < limit; j = i, i += size )
-            {
-                for ( ; compar( j, j + size ) > 0; j -= size )
-                {
-                    memswp( j, j + size, size );
-                    if ( j == base_ )
-                    {
-                        break;
-                    }
-                }
-            }
-            if ( stackptr != stack )           /* if any entries on stack  */
-            {
-                POP( base_, limit );
-            }
-            else                       /* else stack empty, done   */
-            {
-                break;
-            }
-        }
-    }
+#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 *)) {
+  int d=(((last-first)/size)>>3)*size;
+#ifdef DEBUG_QSORT
+fprintf(stderr, "pivot_big: first=%p last=%p size=%lu n=%lu\n", first, (unsigned long)last, size, (unsigned long)((last-first+1)/size));
+#endif
+  char *m1,*m2,*m3;
+  { char *a=first, *b=first+d, *c=first+2*d;
+#ifdef DEBUG_QSORT
+fprintf(stderr,"< %d %d %d @ %p %p %p\n",*(int*)a,*(int*)b,*(int*)c, a,b,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 @ %p %p %p\n",*(int*)a,*(int*)b,*(int*)c, a,b,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 @ %p %p %p\n",*(int*)a,*(int*)b,*(int*)c, a,b,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 @ %p %p %p\n",*(int*)m1,*(int*)m2,*(int*)m3, m1,m2,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));
 }
 
-#endif
+/* ---------------------------------------------------------------------- */
+
+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;
 
-#ifdef TEST
-#include <_PDCLIB_test.h>
-#include <string.h>
-#include <limits.h>
+  if (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-1,size);
+  Insertion(SWAP_nonaligned);
+  free(pivot);
+}
+
+static void qsort_aligned(void *base, size_t nmemb, size_t size,
+           int (*compare)(const void *, const void *)) {
 
-static int compare( const void * left, const void * right )
-{
-    return *( (unsigned char *)left ) - *( (unsigned char *)right );
+  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 (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-1,size);
+  Insertion(SWAP_aligned);
+  free(pivot);
 }
 
-int main( void )
-{
-    char presort[] = { "shreicnyjqpvozxmbt" };
-    char sorted1[] = { "bcehijmnopqrstvxyz" };
-    char sorted2[] = { "bticjqnyozpvreshxm" };
-    char s[19];
-    strcpy( s, presort );
-    qsort( s, 18, 1, compare );
-    TESTCASE( strcmp( s, sorted1 ) == 0 );
-    strcpy( s, presort );
-    qsort( s, 9, 2, compare );
-    TESTCASE( strcmp( s, sorted2 ) == 0 );
-    strcpy( s, presort );
-    qsort( s, 1, 1, compare );
-    TESTCASE( strcmp( s, presort ) == 0 );
-#if defined(REGTEST) && (__BSD_VISIBLE || __APPLE__)
-    puts( "qsort.c: Skipping test #4 for BSD as it goes into endless loop here." );
-#else
-    qsort( s, 100, 0, compare );
-    TESTCASE( strcmp( s, presort ) == 0 );
+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
-    return TEST_RESULTS;
+      /* 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 = %p = #%lu = %d\n", mid, (unsigned long)(((int*)mid)-((int*)base)), *(int*)mid);
+#endif
+      }
+      /* Partition. */
+      Partition(SWAP_words,WORD_BYTES);
+#ifdef DEBUG_QSORT
+fprintf(stderr, "after partitioning first=#%lu last=#%lu\n", (first-(char*)base)/4lu, (last-(char*)base)/4lu);
+#endif
+      /* Prepare to recurse/iterate. */
+      Recurse(TRUNC_words)
+    }
+  }
+  PreInsertion(SWAP_words,(TRUNC_words/WORD_BYTES)-1,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);
 }
 
-#endif
+/* ---------------------------------------------------------------------- */
+
+extern void qsortG(void *base, size_t nmemb, size_t size,
+           int (*compare)(const void *, const void *)) {
+
+  if (nmemb<=1) return;
+  if (((int)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 /* HAVE_QSORT */
 
 /* vi: set ts=4 sw=4 expandtab: */
+