It's now possible to build SDL without any C runtime at all on Windows,
using Visual C++ 2005 --HG-- extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401334
This commit is contained in:
Sam Lantinga
parent
5372bfd326
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101 changed files with 8882 additions and 601 deletions
418
src/stdlib/SDL_qsort.c
Normal file
418
src/stdlib/SDL_qsort.c
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/* qsort.c
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* (c) 1998 Gareth McCaughan
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*
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* This is a drop-in replacement for the C library's |qsort()| routine.
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*
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* Features:
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* - Median-of-three pivoting (and more)
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* - Truncation and final polishing by a single insertion sort
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* - Early truncation when no swaps needed in pivoting step
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* - Explicit recursion, guaranteed not to overflow
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* - A few little wrinkles stolen from the GNU |qsort()|.
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* - separate code for non-aligned / aligned / word-size objects
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*
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* This code may be reproduced freely provided
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* - this file is retained unaltered apart from minor
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* changes for portability and efficiency
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* - no changes are made to this comment
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* - any changes that *are* made are clearly flagged
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* - the _ID string below is altered by inserting, after
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* the date, the string " altered" followed at your option
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* by other material. (Exceptions: you may change the name
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* of the exported routine without changing the ID string.
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* You may change the values of the macros TRUNC_* and
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* PIVOT_THRESHOLD without changing the ID string, provided
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* they remain constants with TRUNC_nonaligned, TRUNC_aligned
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* and TRUNC_words/WORD_BYTES between 8 and 24, and
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* PIVOT_THRESHOLD between 32 and 200.)
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*
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* You may use it in anything you like; you may make money
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* out of it; you may distribute it in object form or as
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* part of an executable without including source code;
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* you don't have to credit me. (But it would be nice if
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* you did.)
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*
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* If you find problems with this code, or find ways of
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* making it significantly faster, please let me know!
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* My e-mail address, valid as of early 1998 and certainly
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* OK for at least the next 18 months, is
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* gjm11@dpmms.cam.ac.uk
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* Thanks!
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*
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* Gareth McCaughan Peterhouse Cambridge 1998
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*/
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/*
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#include <assert.h>
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#include <stdlib.h>
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#include <string.h>
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*/
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#define assert(X)
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#include "SDL_stdlib.h"
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#include "SDL_string.h"
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#ifndef HAVE_QSORT
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static char _ID[]="<qsort.c gjm 1.12 1998-03-19>";
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/* How many bytes are there per word? (Must be a power of 2,
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* and must in fact equal sizeof(int).)
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*/
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#define WORD_BYTES sizeof(int)
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/* How big does our stack need to be? Answer: one entry per
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* bit in a |size_t|.
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*/
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#define STACK_SIZE (8*sizeof(size_t))
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/* Different situations have slightly different requirements,
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* and we make life epsilon easier by using different truncation
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* points for the three different cases.
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* So far, I have tuned TRUNC_words and guessed that the same
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* value might work well for the other two cases. Of course
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* what works well on my machine might work badly on yours.
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*/
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#define TRUNC_nonaligned 12
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#define TRUNC_aligned 12
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#define TRUNC_words 12*WORD_BYTES /* nb different meaning */
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/* We use a simple pivoting algorithm for shortish sub-arrays
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* and a more complicated one for larger ones. The threshold
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* is PIVOT_THRESHOLD.
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*/
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#define PIVOT_THRESHOLD 40
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typedef struct { char * first; char * last; } stack_entry;
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#define pushLeft {stack[stacktop].first=ffirst;stack[stacktop++].last=last;}
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#define pushRight {stack[stacktop].first=first;stack[stacktop++].last=llast;}
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#define doLeft {first=ffirst;llast=last;continue;}
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#define doRight {ffirst=first;last=llast;continue;}
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#define pop {if (--stacktop<0) break;\
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first=ffirst=stack[stacktop].first;\
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last=llast=stack[stacktop].last;\
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continue;}
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/* Some comments on the implementation.
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* 1. When we finish partitioning the array into "low"
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* and "high", we forget entirely about short subarrays,
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* because they'll be done later by insertion sort.
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* Doing lots of little insertion sorts might be a win
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* on large datasets for locality-of-reference reasons,
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* but it makes the code much nastier and increases
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* bookkeeping overhead.
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* 2. We always save the shorter and get to work on the
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* longer. This guarantees that every time we push
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* an item onto the stack its size is <= 1/2 of that
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* of its parent; so the stack can't need more than
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* log_2(max-array-size) entries.
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* 3. We choose a pivot by looking at the first, last
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* and middle elements. We arrange them into order
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* because it's easy to do that in conjunction with
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* choosing the pivot, and it makes things a little
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* easier in the partitioning step. Anyway, the pivot
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* is the middle of these three. It's still possible
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* to construct datasets where the algorithm takes
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* time of order n^2, but it simply never happens in
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* practice.
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* 3' Newsflash: On further investigation I find that
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* it's easy to construct datasets where median-of-3
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* simply isn't good enough. So on large-ish subarrays
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* we do a more sophisticated pivoting: we take three
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* sets of 3 elements, find their medians, and then
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* take the median of those.
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* 4. We copy the pivot element to a separate place
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* because that way we can always do our comparisons
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* directly against a pointer to that separate place,
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* and don't have to wonder "did we move the pivot
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* element?". This makes the inner loop better.
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* 5. It's possible to make the pivoting even more
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* reliable by looking at more candidates when n
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* is larger. (Taking this to its logical conclusion
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* results in a variant of quicksort that doesn't
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* have that n^2 worst case.) However, the overhead
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* from the extra bookkeeping means that it's just
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* not worth while.
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* 6. This is pretty clean and portable code. Here are
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* all the potential portability pitfalls and problems
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* I know of:
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* - In one place (the insertion sort) I construct
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* a pointer that points just past the end of the
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* supplied array, and assume that (a) it won't
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* compare equal to any pointer within the array,
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* and (b) it will compare equal to a pointer
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* obtained by stepping off the end of the array.
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* These might fail on some segmented architectures.
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* - I assume that there are 8 bits in a |char| when
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* computing the size of stack needed. This would
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* fail on machines with 9-bit or 16-bit bytes.
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* - I assume that if |((int)base&(sizeof(int)-1))==0|
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* and |(size&(sizeof(int)-1))==0| then it's safe to
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* get at array elements via |int*|s, and that if
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* actually |size==sizeof(int)| as well then it's
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* safe to treat the elements as |int|s. This might
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* fail on systems that convert pointers to integers
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* in non-standard ways.
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* - I assume that |8*sizeof(size_t)<=INT_MAX|. This
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* would be false on a machine with 8-bit |char|s,
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* 16-bit |int|s and 4096-bit |size_t|s. :-)
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*/
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/* The recursion logic is the same in each case: */
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#define Recurse(Trunc) \
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{ size_t l=last-ffirst,r=llast-first; \
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if (l<Trunc) { \
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if (r>=Trunc) doRight \
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else pop \
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} \
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else if (l<=r) { pushLeft; doRight } \
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else if (r>=Trunc) { pushRight; doLeft }\
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else doLeft \
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}
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/* and so is the pivoting logic: */
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#define Pivot(swapper,sz) \
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if ((size_t)(last-first)>PIVOT_THRESHOLD*sz) mid=pivot_big(first,mid,last,sz,compare);\
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else { \
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if (compare(first,mid)<0) { \
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if (compare(mid,last)>0) { \
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swapper(mid,last); \
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if (compare(first,mid)>0) swapper(first,mid);\
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} \
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} \
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else { \
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if (compare(mid,last)>0) swapper(first,last)\
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else { \
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swapper(first,mid); \
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if (compare(mid,last)>0) swapper(mid,last);\
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} \
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} \
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first+=sz; last-=sz; \
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}
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#ifdef DEBUG_QSORT
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#include <stdio.h>
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#endif
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/* and so is the partitioning logic: */
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#define Partition(swapper,sz) { \
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int swapped=0; \
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do { \
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while (compare(first,pivot)<0) first+=sz; \
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while (compare(pivot,last)<0) last-=sz; \
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if (first<last) { \
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swapper(first,last); swapped=1; \
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first+=sz; last-=sz; } \
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else if (first==last) { first+=sz; last-=sz; break; }\
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} while (first<=last); \
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if (!swapped) pop \
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}
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/* and so is the pre-insertion-sort operation of putting
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* the smallest element into place as a sentinel.
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* Doing this makes the inner loop nicer. I got this
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* idea from the GNU implementation of qsort().
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*/
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#define PreInsertion(swapper,limit,sz) \
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first=base; \
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last=first + (nmemb>limit ? limit : nmemb-1)*sz;\
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while (last!=base) { \
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if (compare(first,last)>0) first=last; \
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last-=sz; } \
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if (first!=base) swapper(first,(char*)base);
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/* and so is the insertion sort, in the first two cases: */
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#define Insertion(swapper) \
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last=((char*)base)+nmemb*size; \
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for (first=((char*)base)+size;first!=last;first+=size) { \
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char *test; \
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/* Find the right place for |first|. \
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* My apologies for var reuse. */ \
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for (test=first-size;compare(test,first)>0;test-=size) ; \
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test+=size; \
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if (test!=first) { \
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/* Shift everything in [test,first) \
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* up by one, and place |first| \
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* where |test| is. */ \
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memcpy(pivot,first,size); \
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memmove(test+size,test,first-test); \
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memcpy(test,pivot,size); \
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} \
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}
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#define SWAP_nonaligned(a,b) { \
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register char *aa=(a),*bb=(b); \
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register size_t sz=size; \
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do { register char t=*aa; *aa++=*bb; *bb++=t; } while (--sz); }
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#define SWAP_aligned(a,b) { \
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register int *aa=(int*)(a),*bb=(int*)(b); \
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register size_t sz=size; \
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do { register int t=*aa;*aa++=*bb; *bb++=t; } while (sz-=WORD_BYTES); }
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#define SWAP_words(a,b) { \
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register int t=*((int*)a); *((int*)a)=*((int*)b); *((int*)b)=t; }
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/* ---------------------------------------------------------------------- */
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static char * pivot_big(char *first, char *mid, char *last, size_t size,
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int compare(const void *, const void *)) {
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int d=(((last-first)/size)>>3)*size;
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char *m1,*m2,*m3;
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{ char *a=first, *b=first+d, *c=first+2*d;
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#ifdef DEBUG_QSORT
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fprintf(stderr,"< %d %d %d\n",*(int*)a,*(int*)b,*(int*)c);
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#endif
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m1 = compare(a,b)<0 ?
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(compare(b,c)<0 ? b : (compare(a,c)<0 ? c : a))
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: (compare(a,c)<0 ? a : (compare(b,c)<0 ? c : b));
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}
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{ char *a=mid-d, *b=mid, *c=mid+d;
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#ifdef DEBUG_QSORT
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fprintf(stderr,". %d %d %d\n",*(int*)a,*(int*)b,*(int*)c);
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#endif
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m2 = compare(a,b)<0 ?
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(compare(b,c)<0 ? b : (compare(a,c)<0 ? c : a))
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: (compare(a,c)<0 ? a : (compare(b,c)<0 ? c : b));
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}
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{ char *a=last-2*d, *b=last-d, *c=last;
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#ifdef DEBUG_QSORT
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fprintf(stderr,"> %d %d %d\n",*(int*)a,*(int*)b,*(int*)c);
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#endif
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m3 = compare(a,b)<0 ?
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(compare(b,c)<0 ? b : (compare(a,c)<0 ? c : a))
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: (compare(a,c)<0 ? a : (compare(b,c)<0 ? c : b));
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}
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#ifdef DEBUG_QSORT
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fprintf(stderr,"-> %d %d %d\n",*(int*)m1,*(int*)m2,*(int*)m3);
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#endif
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return compare(m1,m2)<0 ?
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(compare(m2,m3)<0 ? m2 : (compare(m1,m3)<0 ? m3 : m1))
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: (compare(m1,m3)<0 ? m1 : (compare(m2,m3)<0 ? m3 : m2));
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}
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/* ---------------------------------------------------------------------- */
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static void qsort_nonaligned(void *base, size_t nmemb, size_t size,
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int (*compare)(const void *, const void *)) {
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stack_entry stack[STACK_SIZE];
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int stacktop=0;
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char *first,*last;
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char *pivot=malloc(size);
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size_t trunc=TRUNC_nonaligned*size;
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assert(pivot!=0);
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first=(char*)base; last=first+(nmemb-1)*size;
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if ((size_t)(last-first)>trunc) {
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char *ffirst=first, *llast=last;
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while (1) {
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/* Select pivot */
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{ char * mid=first+size*((last-first)/size >> 1);
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Pivot(SWAP_nonaligned,size);
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memcpy(pivot,mid,size);
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}
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/* Partition. */
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Partition(SWAP_nonaligned,size);
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/* Prepare to recurse/iterate. */
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Recurse(trunc)
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}
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}
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PreInsertion(SWAP_nonaligned,TRUNC_nonaligned,size);
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Insertion(SWAP_nonaligned);
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free(pivot);
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}
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static void qsort_aligned(void *base, size_t nmemb, size_t size,
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int (*compare)(const void *, const void *)) {
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stack_entry stack[STACK_SIZE];
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int stacktop=0;
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char *first,*last;
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char *pivot=malloc(size);
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size_t trunc=TRUNC_aligned*size;
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assert(pivot!=0);
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first=(char*)base; last=first+(nmemb-1)*size;
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if ((size_t)(last-first)>trunc) {
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char *ffirst=first,*llast=last;
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while (1) {
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/* Select pivot */
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{ char * mid=first+size*((last-first)/size >> 1);
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Pivot(SWAP_aligned,size);
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memcpy(pivot,mid,size);
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}
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/* Partition. */
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Partition(SWAP_aligned,size);
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/* Prepare to recurse/iterate. */
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Recurse(trunc)
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}
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}
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PreInsertion(SWAP_aligned,TRUNC_aligned,size);
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Insertion(SWAP_aligned);
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free(pivot);
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}
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static void qsort_words(void *base, size_t nmemb,
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int (*compare)(const void *, const void *)) {
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stack_entry stack[STACK_SIZE];
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int stacktop=0;
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char *first,*last;
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char *pivot=malloc(WORD_BYTES);
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assert(pivot!=0);
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first=(char*)base; last=first+(nmemb-1)*WORD_BYTES;
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if (last-first>TRUNC_words) {
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char *ffirst=first, *llast=last;
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while (1) {
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#ifdef DEBUG_QSORT
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fprintf(stderr,"Doing %d:%d: ",
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(first-(char*)base)/WORD_BYTES,
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(last-(char*)base)/WORD_BYTES);
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#endif
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/* Select pivot */
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{ char * mid=first+WORD_BYTES*((last-first) / (2*WORD_BYTES));
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Pivot(SWAP_words,WORD_BYTES);
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*(int*)pivot=*(int*)mid;
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}
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#ifdef DEBUG_QSORT
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fprintf(stderr,"pivot=%d\n",*(int*)pivot);
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#endif
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/* Partition. */
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Partition(SWAP_words,WORD_BYTES);
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/* Prepare to recurse/iterate. */
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Recurse(TRUNC_words)
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}
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}
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PreInsertion(SWAP_words,(TRUNC_words/WORD_BYTES),WORD_BYTES);
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/* Now do insertion sort. */
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last=((char*)base)+nmemb*WORD_BYTES;
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for (first=((char*)base)+WORD_BYTES;first!=last;first+=WORD_BYTES) {
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/* Find the right place for |first|. My apologies for var reuse */
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int *pl=(int*)(first-WORD_BYTES),*pr=(int*)first;
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*(int*)pivot=*(int*)first;
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for (;compare(pl,pivot)>0;pr=pl,--pl) {
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*pr=*pl; }
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if (pr!=(int*)first) *pr=*(int*)pivot;
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}
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free(pivot);
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}
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/* ---------------------------------------------------------------------- */
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void SDL_qsort(void *base, size_t nmemb, size_t size,
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int (*compare)(const void *, const void *)) {
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if (nmemb<=1) return;
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if (((int)base|size)&(WORD_BYTES-1))
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qsort_nonaligned(base,nmemb,size,compare);
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else if (size!=WORD_BYTES)
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qsort_aligned(base,nmemb,size,compare);
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else
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qsort_words(base,nmemb,compare);
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}
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#endif /* !HAVE_QSORT */
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