skia / third_party / sdl / 9d7ab323461e9c23545e2ad9d1d4b14dbd9f21b0 / . / src / stdlib / SDL_qsort.c

/* | |

Simple DirectMedia Layer | |

Copyright (C) 1997-2020 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" | |

#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 SDL_assert | |

#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 qsortG | |

#undef qsortG | |

#endif | |

#define qsortG SDL_qsort | |

/* | |

This code came from Gareth McCaughan, under the zlib license. | |

Specifically this: https://www.mccaughan.org.uk/software/qsort.c-1.15 | |

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. | |

*/ | |

/* 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 | |

*/ | |

/* 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. | |

* 2016-03-10 v1.15 Fix bug kindly reported by Ryan Gordon | |

* (pre-insertion-sort messed up). | |

* Disable DEBUG_QSORT by default. | |

* Tweak comments very slightly. | |

*/ | |

/* BEGIN SDL CHANGE ... commented this out with an #if 0 block. --ryan. */ | |

#if 0 | |

#include <assert.h> | |

#include <stdlib.h> | |

#include <string.h> | |

#undef DEBUG_QSORT | |

static char _ID[]="<qsort.c gjm 1.15 2016-03-10>"; | |

#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) | |

/* 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. | |

* 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 ((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) { \ | |

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); \ | |

} | |

/* 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| (because our | |

* quicksort recursion bottoms out only once we | |

* reach subarrays smaller than |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); | |

/* 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; | |

#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)); | |

} | |

/* ---------------------------------------------------------------------- */ | |

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 = %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,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); | |

} | |

/* ---------------------------------------------------------------------- */ | |

extern void qsortG(void *base, size_t nmemb, size_t size, | |

int (*compare)(const void *, const void *)) { | |

if (nmemb<=1) return; | |

if (((size_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 /* HAVE_QSORT */ | |

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