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Diffstat (limited to 'distrib/sdl-1.2.15/src/stdlib/SDL_qsort.c')
| -rw-r--r-- | distrib/sdl-1.2.15/src/stdlib/SDL_qsort.c | 443 |
1 files changed, 443 insertions, 0 deletions
diff --git a/distrib/sdl-1.2.15/src/stdlib/SDL_qsort.c b/distrib/sdl-1.2.15/src/stdlib/SDL_qsort.c new file mode 100644 index 0000000..2b5abea --- /dev/null +++ b/distrib/sdl-1.2.15/src/stdlib/SDL_qsort.c @@ -0,0 +1,443 @@ +/* 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" + +#ifdef assert +#undef assert +#endif +#define 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 + + +#ifndef HAVE_QSORT + +static 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 /* !HAVE_QSORT */ |