2 Simple DirectMedia Layer
3 Copyright (C) 1997-2018 Sam Lantinga <slouken@libsdl.org>
5 This software is provided 'as-is', without any express or implied
6 warranty. In no event will the authors be held liable for any damages
7 arising from the use of this software.
9 Permission is granted to anyone to use this software for any purpose,
10 including commercial applications, and to alter it and redistribute it
11 freely, subject to the following restrictions:
13 1. The origin of this software must not be misrepresented; you must not
14 claim that you wrote the original software. If you use this software
15 in a product, an acknowledgment in the product documentation would be
16 appreciated but is not required.
17 2. Altered source versions must be plainly marked as such, and must not be
18 misrepresented as being the original software.
19 3. This notice may not be removed or altered from any source distribution.
22 #if defined(__clang_analyzer__) && !defined(SDL_DISABLE_ANALYZE_MACROS)
23 #define SDL_DISABLE_ANALYZE_MACROS 1
26 #include "../SDL_internal.h"
28 #include "SDL_stdinc.h"
29 #include "SDL_assert.h"
31 #if defined(HAVE_QSORT)
33 SDL_qsort(void *base, size_t nmemb, size_t size, int (*compare) (const void *, const void *))
35 qsort(base, nmemb, size, compare);
43 #define assert SDL_assert
47 #define malloc SDL_malloc
55 #define memcpy SDL_memcpy
59 #define memmove SDL_memmove
63 #define qsortG SDL_qsort
66 This code came from Gareth McCaughan, under the zlib license.
67 Specifically this: https://www.mccaughan.org.uk/software/qsort.c-1.14
69 Everything below this comment until the HAVE_QSORT #endif was from Gareth
70 (any minor changes will be noted inline).
72 Thank you to Gareth for relicensing this code under the zlib license for our
78 /* This is a drop-in replacement for the C library's |qsort()| routine.
80 * It is intended for use where you know or suspect that your
81 * platform's qsort is bad. If that isn't the case, then you
82 * should probably use the qsort your system gives you in preference
83 * to mine -- it will likely have been tested and tuned better.
86 * - Median-of-three pivoting (and more)
87 * - Truncation and final polishing by a single insertion sort
88 * - Early truncation when no swaps needed in pivoting step
89 * - Explicit recursion, guaranteed not to overflow
90 * - A few little wrinkles stolen from the GNU |qsort()|.
91 * (For the avoidance of doubt, no code was stolen, only
93 * - separate code for non-aligned / aligned / word-size objects
95 * Earlier releases of this code used an idiosyncratic licence
96 * I wrote myself, because I'm an idiot. The code is now released
97 * under the "zlib/libpng licence"; you will find the actual
98 * terms in the next comment. I request (but do not require)
99 * that if you make any changes beyond the name of the exported
100 * routine and reasonable tweaks to the TRUNC_* and
101 * PIVOT_THRESHOLD values, you modify the _ID string so as
102 * to make it clear that you have changed the code.
104 * If you find problems with this code, or find ways of
105 * making it significantly faster, please let me know!
106 * My e-mail address, valid as of early 2016 and for the
107 * foreseeable future, is
108 * gareth.mccaughan@pobox.com
114 /* Copyright (c) 1998-2016 Gareth McCaughan
116 * This software is provided 'as-is', without any express or implied
117 * warranty. In no event will the authors be held liable for any
118 * damages arising from the use of this software.
120 * Permission is granted to anyone to use this software for any purpose,
121 * including commercial applications, and to alter it and redistribute it
122 * freely, subject to the following restrictions:
124 * 1. The origin of this software must not be misrepresented;
125 * you must not claim that you wrote the original software.
126 * If you use this software in a product, an acknowledgment
127 * in the product documentation would be appreciated but
130 * 2. Altered source versions must be plainly marked as such,
131 * and must not be misrepresented as being the original software.
133 * 3. This notice may not be removed or altered from any source
137 /* Revision history since release:
138 * 1998-03-19 v1.12 First release I have any records of.
139 * 2007-09-02 v1.13 Fix bug kindly reported by Dan Bodoh
140 * (premature termination of recursion).
141 * Add a few clarifying comments.
142 * Minor improvements to debug output.
143 * 2016-02-21 v1.14 Replace licence with 2-clause BSD,
144 * and clarify a couple of things in
145 * comments. No code changes.
148 /* BEGIN SDL CHANGE ... commented this out with an #if 0 block. --ryan. */
156 static char _ID[]="<qsort.c gjm 1.14 2016-02-21>";
158 /* END SDL CHANGE ... commented this out with an #if 0 block. --ryan. */
160 /* How many bytes are there per word? (Must be a power of 2,
161 * and must in fact equal sizeof(int).)
163 #define WORD_BYTES sizeof(int)
165 /* How big does our stack need to be? Answer: one entry per
168 #define STACK_SIZE (8*sizeof(size_t))
170 /* Different situations have slightly different requirements,
171 * and we make life epsilon easier by using different truncation
172 * points for the three different cases.
173 * So far, I have tuned TRUNC_words and guessed that the same
174 * value might work well for the other two cases. Of course
175 * what works well on my machine might work badly on yours.
177 #define TRUNC_nonaligned 12
178 #define TRUNC_aligned 12
179 #define TRUNC_words 12*WORD_BYTES /* nb different meaning */
181 /* We use a simple pivoting algorithm for shortish sub-arrays
182 * and a more complicated one for larger ones. The threshold
183 * is PIVOT_THRESHOLD.
185 #define PIVOT_THRESHOLD 40
187 typedef struct { char * first; char * last; } stack_entry;
188 #define pushLeft {stack[stacktop].first=ffirst;stack[stacktop++].last=last;}
189 #define pushRight {stack[stacktop].first=first;stack[stacktop++].last=llast;}
190 #define doLeft {first=ffirst;llast=last;continue;}
191 #define doRight {ffirst=first;last=llast;continue;}
192 #define pop {if (--stacktop<0) break;\
193 first=ffirst=stack[stacktop].first;\
194 last=llast=stack[stacktop].last;\
197 /* Some comments on the implementation.
198 * 1. When we finish partitioning the array into "low"
199 * and "high", we forget entirely about short subarrays,
200 * because they'll be done later by insertion sort.
201 * Doing lots of little insertion sorts might be a win
202 * on large datasets for locality-of-reference reasons,
203 * but it makes the code much nastier and increases
204 * bookkeeping overhead.
205 * 2. We always save the shorter and get to work on the
206 * longer. This guarantees that every time we push
207 * an item onto the stack its size is <= 1/2 of that
208 * of its parent; so the stack can't need more than
209 * log_2(max-array-size) entries.
210 * 3. We choose a pivot by looking at the first, last
211 * and middle elements. We arrange them into order
212 * because it's easy to do that in conjunction with
213 * choosing the pivot, and it makes things a little
214 * easier in the partitioning step. Anyway, the pivot
215 * is the middle of these three. It's still possible
216 * to construct datasets where the algorithm takes
217 * time of order n^2, but it simply never happens in
219 * 3' Newsflash: On further investigation I find that
220 * it's easy to construct datasets where median-of-3
221 * simply isn't good enough. So on large-ish subarrays
222 * we do a more sophisticated pivoting: we take three
223 * sets of 3 elements, find their medians, and then
224 * take the median of those.
225 * 4. We copy the pivot element to a separate place
226 * because that way we can always do our comparisons
227 * directly against a pointer to that separate place,
228 * and don't have to wonder "did we move the pivot
229 * element?". This makes the inner loop better.
230 * 5. It's possible to make the pivoting even more
231 * reliable by looking at more candidates when n
232 * is larger. (Taking this to its logical conclusion
233 * results in a variant of quicksort that doesn't
234 * have that n^2 worst case.) However, the overhead
235 * from the extra bookkeeping means that it's just
237 * 6. This is pretty clean and portable code. Here are
238 * all the potential portability pitfalls and problems
240 * - In one place (the insertion sort) I construct
241 * a pointer that points just past the end of the
242 * supplied array, and assume that (a) it won't
243 * compare equal to any pointer within the array,
244 * and (b) it will compare equal to a pointer
245 * obtained by stepping off the end of the array.
246 * These might fail on some segmented architectures.
247 * - I assume that there are 8 bits in a |char| when
248 * computing the size of stack needed. This would
249 * fail on machines with 9-bit or 16-bit bytes.
250 * - I assume that if |((int)base&(sizeof(int)-1))==0|
251 * and |(size&(sizeof(int)-1))==0| then it's safe to
252 * get at array elements via |int*|s, and that if
253 * actually |size==sizeof(int)| as well then it's
254 * safe to treat the elements as |int|s. This might
255 * fail on systems that convert pointers to integers
256 * in non-standard ways.
257 * - I assume that |8*sizeof(size_t)<=INT_MAX|. This
258 * would be false on a machine with 8-bit |char|s,
259 * 16-bit |int|s and 4096-bit |size_t|s. :-)
262 /* The recursion logic is the same in each case.
263 * We keep chopping up until we reach subarrays of size
264 * strictly less than Trunc; we leave these unsorted. */
265 #define Recurse(Trunc) \
266 { size_t l=last-ffirst,r=llast-first; \
268 if (r>=Trunc) doRight \
271 else if (l<=r) { pushLeft; doRight } \
272 else if (r>=Trunc) { pushRight; doLeft }\
276 /* and so is the pivoting logic (note: last is inclusive): */
277 #define Pivot(swapper,sz) \
278 if ((size_t)(last-first)>PIVOT_THRESHOLD*sz) mid=pivot_big(first,mid,last,sz,compare);\
280 if (compare(first,mid)<0) { \
281 if (compare(mid,last)>0) { \
283 if (compare(first,mid)>0) swapper(first,mid);\
287 if (compare(mid,last)>0) swapper(first,last)\
289 swapper(first,mid); \
290 if (compare(mid,last)>0) swapper(mid,last);\
293 first+=sz; last-=sz; \
300 /* and so is the partitioning logic: */
301 #define Partition(swapper,sz) { \
303 while (compare(first,pivot)<0) first+=sz; \
304 while (compare(pivot,last)<0) last-=sz; \
306 swapper(first,last); \
307 first+=sz; last-=sz; } \
308 else if (first==last) { first+=sz; last-=sz; break; }\
309 } while (first<=last); \
312 /* and so is the pre-insertion-sort operation of putting
313 * the smallest element into place as a sentinel.
314 * Doing this makes the inner loop nicer. I got this
315 * idea from the GNU implementation of qsort().
316 * We find the smallest element from the first |nmemb|,
317 * or the first |limit|, whichever is smaller;
318 * therefore we must have ensured that the globally smallest
319 * element is in the first |limit|.
321 #define PreInsertion(swapper,limit,sz) \
323 last=first + ((nmemb>limit ? limit : nmemb)-1)*sz;\
324 while (last!=base) { \
325 if (compare(first,last)>0) first=last; \
327 if (first!=base) swapper(first,(char*)base);
329 /* and so is the insertion sort, in the first two cases: */
330 #define Insertion(swapper) \
331 last=((char*)base)+nmemb*size; \
332 for (first=((char*)base)+size;first!=last;first+=size) { \
334 /* Find the right place for |first|. \
335 * My apologies for var reuse. */ \
336 for (test=first-size;compare(test,first)>0;test-=size) ; \
339 /* Shift everything in [test,first) \
340 * up by one, and place |first| \
341 * where |test| is. */ \
342 memcpy(pivot,first,size); \
343 memmove(test+size,test,first-test); \
344 memcpy(test,pivot,size); \
348 #define SWAP_nonaligned(a,b) { \
349 register char *aa=(a),*bb=(b); \
350 register size_t sz=size; \
351 do { register char t=*aa; *aa++=*bb; *bb++=t; } while (--sz); }
353 #define SWAP_aligned(a,b) { \
354 register int *aa=(int*)(a),*bb=(int*)(b); \
355 register size_t sz=size; \
356 do { register int t=*aa;*aa++=*bb; *bb++=t; } while (sz-=WORD_BYTES); }
358 #define SWAP_words(a,b) { \
359 register int t=*((int*)a); *((int*)a)=*((int*)b); *((int*)b)=t; }
361 /* ---------------------------------------------------------------------- */
363 static char * pivot_big(char *first, char *mid, char *last, size_t size,
364 int compare(const void *, const void *)) {
365 size_t d=(((last-first)/size)>>3)*size;
367 fprintf(stderr, "pivot_big: first=%p last=%p size=%lu n=%lu\n", first, (unsigned long)last, size, (unsigned long)((last-first+1)/size));
370 { char *a=first, *b=first+d, *c=first+2*d;
372 fprintf(stderr,"< %d %d %d @ %p %p %p\n",*(int*)a,*(int*)b,*(int*)c, a,b,c);
374 m1 = compare(a,b)<0 ?
375 (compare(b,c)<0 ? b : (compare(a,c)<0 ? c : a))
376 : (compare(a,c)<0 ? a : (compare(b,c)<0 ? c : b));
378 { char *a=mid-d, *b=mid, *c=mid+d;
380 fprintf(stderr,". %d %d %d @ %p %p %p\n",*(int*)a,*(int*)b,*(int*)c, a,b,c);
382 m2 = compare(a,b)<0 ?
383 (compare(b,c)<0 ? b : (compare(a,c)<0 ? c : a))
384 : (compare(a,c)<0 ? a : (compare(b,c)<0 ? c : b));
386 { char *a=last-2*d, *b=last-d, *c=last;
388 fprintf(stderr,"> %d %d %d @ %p %p %p\n",*(int*)a,*(int*)b,*(int*)c, a,b,c);
390 m3 = compare(a,b)<0 ?
391 (compare(b,c)<0 ? b : (compare(a,c)<0 ? c : a))
392 : (compare(a,c)<0 ? a : (compare(b,c)<0 ? c : b));
395 fprintf(stderr,"-> %d %d %d @ %p %p %p\n",*(int*)m1,*(int*)m2,*(int*)m3, m1,m2,m3);
397 return compare(m1,m2)<0 ?
398 (compare(m2,m3)<0 ? m2 : (compare(m1,m3)<0 ? m3 : m1))
399 : (compare(m1,m3)<0 ? m1 : (compare(m2,m3)<0 ? m3 : m2));
402 /* ---------------------------------------------------------------------- */
404 static void qsort_nonaligned(void *base, size_t nmemb, size_t size,
405 int (*compare)(const void *, const void *)) {
407 stack_entry stack[STACK_SIZE];
410 char *pivot=malloc(size);
411 size_t trunc=TRUNC_nonaligned*size;
414 first=(char*)base; last=first+(nmemb-1)*size;
416 if ((size_t)(last-first)>=trunc) {
417 char *ffirst=first, *llast=last;
420 { char * mid=first+size*((last-first)/size >> 1);
421 Pivot(SWAP_nonaligned,size);
422 memcpy(pivot,mid,size);
425 Partition(SWAP_nonaligned,size);
426 /* Prepare to recurse/iterate. */
430 PreInsertion(SWAP_nonaligned,TRUNC_nonaligned,size);
431 Insertion(SWAP_nonaligned);
435 static void qsort_aligned(void *base, size_t nmemb, size_t size,
436 int (*compare)(const void *, const void *)) {
438 stack_entry stack[STACK_SIZE];
441 char *pivot=malloc(size);
442 size_t trunc=TRUNC_aligned*size;
445 first=(char*)base; last=first+(nmemb-1)*size;
447 if ((size_t)(last-first)>=trunc) {
448 char *ffirst=first,*llast=last;
451 { char * mid=first+size*((last-first)/size >> 1);
452 Pivot(SWAP_aligned,size);
453 memcpy(pivot,mid,size);
456 Partition(SWAP_aligned,size);
457 /* Prepare to recurse/iterate. */
461 PreInsertion(SWAP_aligned,TRUNC_aligned,size);
462 Insertion(SWAP_aligned);
466 static void qsort_words(void *base, size_t nmemb,
467 int (*compare)(const void *, const void *)) {
469 stack_entry stack[STACK_SIZE];
472 char *pivot=malloc(WORD_BYTES);
475 first=(char*)base; last=first+(nmemb-1)*WORD_BYTES;
477 if (last-first>=TRUNC_words) {
478 char *ffirst=first, *llast=last;
481 fprintf(stderr,"Doing %d:%d: ",
482 (first-(char*)base)/WORD_BYTES,
483 (last-(char*)base)/WORD_BYTES);
486 { char * mid=first+WORD_BYTES*((last-first) / (2*WORD_BYTES));
487 Pivot(SWAP_words,WORD_BYTES);
488 *(int*)pivot=*(int*)mid;
490 fprintf(stderr,"pivot = %p = #%lu = %d\n", mid, (unsigned long)(((int*)mid)-((int*)base)), *(int*)mid);
494 Partition(SWAP_words,WORD_BYTES);
496 fprintf(stderr, "after partitioning first=#%lu last=#%lu\n", (first-(char*)base)/4lu, (last-(char*)base)/4lu);
498 /* Prepare to recurse/iterate. */
502 PreInsertion(SWAP_words,(TRUNC_words/WORD_BYTES),WORD_BYTES);
503 /* Now do insertion sort. */
504 last=((char*)base)+nmemb*WORD_BYTES;
505 for (first=((char*)base)+WORD_BYTES;first!=last;first+=WORD_BYTES) {
506 /* Find the right place for |first|. My apologies for var reuse */
507 int *pl=(int*)(first-WORD_BYTES),*pr=(int*)first;
508 *(int*)pivot=*(int*)first;
509 for (;compare(pl,pivot)>0;pr=pl,--pl) {
511 if (pr!=(int*)first) *pr=*(int*)pivot;
516 /* ---------------------------------------------------------------------- */
518 extern void qsortG(void *base, size_t nmemb, size_t size,
519 int (*compare)(const void *, const void *)) {
521 if (nmemb<=1) return;
522 if (((size_t)base|size)&(WORD_BYTES-1))
523 qsort_nonaligned(base,nmemb,size,compare);
524 else if (size!=WORD_BYTES)
525 qsort_aligned(base,nmemb,size,compare);
527 qsort_words(base,nmemb,compare);
531 #endif /* HAVE_QSORT */
533 /* vi: set ts=4 sw=4 expandtab: */