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annotate src/stdlib/SDL_qsort.c @ 3035:ff602fdfdedc

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Removed Rafal Bursig's MMX RLE code, at his request.
author Sam Lantinga <slouken@libsdl.org>
date Tue, 13 Jan 2009 07:20:55 +0000
parents c121d94672cb
children dc1eb82ffdaa
rev   line source
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450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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1 /* qsort.c
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2 * (c) 1998 Gareth McCaughan
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3 *
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4 * This is a drop-in replacement for the C library's |qsort()| routine.
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5 *
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6 * Features:
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7 * - Median-of-three pivoting (and more)
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8 * - Truncation and final polishing by a single insertion sort
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9 * - Early truncation when no swaps needed in pivoting step
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10 * - Explicit recursion, guaranteed not to overflow
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11 * - A few little wrinkles stolen from the GNU |qsort()|.
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12 * - separate code for non-aligned / aligned / word-size objects
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13 *
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14 * This code may be reproduced freely provided
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15 * - this file is retained unaltered apart from minor
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16 * changes for portability and efficiency
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17 * - no changes are made to this comment
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18 * - any changes that *are* made are clearly flagged
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19 * - the _ID string below is altered by inserting, after
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20 * the date, the string " altered" followed at your option
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21 * by other material. (Exceptions: you may change the name
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22 * of the exported routine without changing the ID string.
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23 * You may change the values of the macros TRUNC_* and
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24 * PIVOT_THRESHOLD without changing the ID string, provided
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25 * they remain constants with TRUNC_nonaligned, TRUNC_aligned
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26 * and TRUNC_words/WORD_BYTES between 8 and 24, and
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27 * PIVOT_THRESHOLD between 32 and 200.)
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28 *
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29 * You may use it in anything you like; you may make money
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30 * out of it; you may distribute it in object form or as
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31 * part of an executable without including source code;
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32 * you don't have to credit me. (But it would be nice if
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33 * you did.)
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34 *
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35 * If you find problems with this code, or find ways of
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36 * making it significantly faster, please let me know!
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37 * My e-mail address, valid as of early 1998 and certainly
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38 * OK for at least the next 18 months, is
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39 * gjm11@dpmms.cam.ac.uk
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40 * Thanks!
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41 *
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42 * Gareth McCaughan Peterhouse Cambridge 1998
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43 */
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44 #include "SDL_config.h"
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45
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46 /*
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47 #include <assert.h>
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48 #include <stdlib.h>
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49 #include <string.h>
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50 */
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51 #include "SDL_stdinc.h"
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52
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53 #define assert(X)
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54 #define malloc SDL_malloc
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55 #define free SDL_free
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56 #define memcpy SDL_memcpy
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57 #define memmove SDL_memmove
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58 #define qsort SDL_qsort
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59
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60
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61 #ifndef HAVE_QSORT
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62
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63 static char _ID[] = "<qsort.c gjm 1.12 1998-03-19>";
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64
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65 /* How many bytes are there per word? (Must be a power of 2,
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66 * and must in fact equal sizeof(int).)
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67 */
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68 #define WORD_BYTES sizeof(int)
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69
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70 /* How big does our stack need to be? Answer: one entry per
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71 * bit in a |size_t|.
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72 */
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73 #define STACK_SIZE (8*sizeof(size_t))
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74
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75 /* Different situations have slightly different requirements,
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76 * and we make life epsilon easier by using different truncation
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77 * points for the three different cases.
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78 * So far, I have tuned TRUNC_words and guessed that the same
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79 * value might work well for the other two cases. Of course
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80 * what works well on my machine might work badly on yours.
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81 */
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82 #define TRUNC_nonaligned 12
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83 #define TRUNC_aligned 12
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84 #define TRUNC_words 12*WORD_BYTES /* nb different meaning */
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85
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86 /* We use a simple pivoting algorithm for shortish sub-arrays
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87 * and a more complicated one for larger ones. The threshold
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88 * is PIVOT_THRESHOLD.
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89 */
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90 #define PIVOT_THRESHOLD 40
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91
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92 typedef struct
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93 {
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94 char *first;
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95 char *last;
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96 } stack_entry;
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97 #define pushLeft {stack[stacktop].first=ffirst;stack[stacktop++].last=last;}
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98 #define pushRight {stack[stacktop].first=first;stack[stacktop++].last=llast;}
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99 #define doLeft {first=ffirst;llast=last;continue;}
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100 #define doRight {ffirst=first;last=llast;continue;}
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101 #define pop {if (--stacktop<0) break;\
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102 first=ffirst=stack[stacktop].first;\
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103 last=llast=stack[stacktop].last;\
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104 continue;}
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105
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106 /* Some comments on the implementation.
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107 * 1. When we finish partitioning the array into "low"
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108 * and "high", we forget entirely about short subarrays,
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109 * because they'll be done later by insertion sort.
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110 * Doing lots of little insertion sorts might be a win
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111 * on large datasets for locality-of-reference reasons,
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112 * but it makes the code much nastier and increases
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113 * bookkeeping overhead.
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114 * 2. We always save the shorter and get to work on the
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115 * longer. This guarantees that every time we push
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116 * an item onto the stack its size is <= 1/2 of that
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117 * of its parent; so the stack can't need more than
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118 * log_2(max-array-size) entries.
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119 * 3. We choose a pivot by looking at the first, last
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120 * and middle elements. We arrange them into order
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121 * because it's easy to do that in conjunction with
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122 * choosing the pivot, and it makes things a little
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123 * easier in the partitioning step. Anyway, the pivot
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124 * is the middle of these three. It's still possible
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125 * to construct datasets where the algorithm takes
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126 * time of order n^2, but it simply never happens in
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127 * practice.
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128 * 3' Newsflash: On further investigation I find that
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129 * it's easy to construct datasets where median-of-3
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130 * simply isn't good enough. So on large-ish subarrays
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131 * we do a more sophisticated pivoting: we take three
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132 * sets of 3 elements, find their medians, and then
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133 * take the median of those.
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134 * 4. We copy the pivot element to a separate place
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135 * because that way we can always do our comparisons
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136 * directly against a pointer to that separate place,
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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137 * and don't have to wonder "did we move the pivot
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138 * element?". This makes the inner loop better.
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139 * 5. It's possible to make the pivoting even more
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140 * reliable by looking at more candidates when n
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141 * is larger. (Taking this to its logical conclusion
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142 * results in a variant of quicksort that doesn't
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143 * have that n^2 worst case.) However, the overhead
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144 * from the extra bookkeeping means that it's just
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145 * not worth while.
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146 * 6. This is pretty clean and portable code. Here are
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147 * all the potential portability pitfalls and problems
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148 * I know of:
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149 * - In one place (the insertion sort) I construct
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150 * a pointer that points just past the end of the
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151 * supplied array, and assume that (a) it won't
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152 * compare equal to any pointer within the array,
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153 * and (b) it will compare equal to a pointer
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154 * obtained by stepping off the end of the array.
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155 * These might fail on some segmented architectures.
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156 * - I assume that there are 8 bits in a |char| when
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157 * computing the size of stack needed. This would
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158 * fail on machines with 9-bit or 16-bit bytes.
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159 * - I assume that if |((int)base&(sizeof(int)-1))==0|
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160 * and |(size&(sizeof(int)-1))==0| then it's safe to
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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161 * get at array elements via |int*|s, and that if
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162 * actually |size==sizeof(int)| as well then it's
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163 * safe to treat the elements as |int|s. This might
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164 * fail on systems that convert pointers to integers
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165 * in non-standard ways.
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166 * - I assume that |8*sizeof(size_t)<=INT_MAX|. This
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167 * would be false on a machine with 8-bit |char|s,
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168 * 16-bit |int|s and 4096-bit |size_t|s. :-)
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169 */
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170
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171 /* The recursion logic is the same in each case: */
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172 #define Recurse(Trunc) \
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173 { size_t l=last-ffirst,r=llast-first; \
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174 if (l<Trunc) { \
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175 if (r>=Trunc) doRight \
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176 else pop \
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177 } \
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178 else if (l<=r) { pushLeft; doRight } \
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179 else if (r>=Trunc) { pushRight; doLeft }\
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180 else doLeft \
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181 }
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182
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183 /* and so is the pivoting logic: */
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184 #define Pivot(swapper,sz) \
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185 if ((size_t)(last-first)>PIVOT_THRESHOLD*sz) mid=pivot_big(first,mid,last,sz,compare);\
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186 else { \
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187 if (compare(first,mid)<0) { \
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188 if (compare(mid,last)>0) { \
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189 swapper(mid,last); \
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190 if (compare(first,mid)>0) swapper(first,mid);\
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191 } \
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192 } \
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193 else { \
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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194 if (compare(mid,last)>0) swapper(first,last)\
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195 else { \
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196 swapper(first,mid); \
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197 if (compare(mid,last)>0) swapper(mid,last);\
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198 } \
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199 } \
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200 first+=sz; last-=sz; \
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201 }
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202
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203 #ifdef DEBUG_QSORT
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204 #include <stdio.h>
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205 #endif
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206
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207 /* and so is the partitioning logic: */
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208 #define Partition(swapper,sz) { \
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209 int swapped=0; \
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210 do { \
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211 while (compare(first,pivot)<0) first+=sz; \
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212 while (compare(pivot,last)<0) last-=sz; \
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213 if (first<last) { \
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214 swapper(first,last); swapped=1; \
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215 first+=sz; last-=sz; } \
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216 else if (first==last) { first+=sz; last-=sz; break; }\
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217 } while (first<=last); \
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218 if (!swapped) pop \
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219 }
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220
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221 /* and so is the pre-insertion-sort operation of putting
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222 * the smallest element into place as a sentinel.
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223 * Doing this makes the inner loop nicer. I got this
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224 * idea from the GNU implementation of qsort().
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225 */
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226 #define PreInsertion(swapper,limit,sz) \
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227 first=base; \
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228 last=first + (nmemb>limit ? limit : nmemb-1)*sz;\
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229 while (last!=base) { \
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230 if (compare(first,last)>0) first=last; \
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231 last-=sz; } \
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232 if (first!=base) swapper(first,(char*)base);
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233
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234 /* and so is the insertion sort, in the first two cases: */
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235 #define Insertion(swapper) \
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236 last=((char*)base)+nmemb*size; \
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237 for (first=((char*)base)+size;first!=last;first+=size) { \
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238 char *test; \
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239 /* Find the right place for |first|. \
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240 * My apologies for var reuse. */ \
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241 for (test=first-size;compare(test,first)>0;test-=size) ; \
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242 test+=size; \
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243 if (test!=first) { \
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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244 /* Shift everything in [test,first) \
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245 * up by one, and place |first| \
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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246 * where |test| is. */ \
1337
c687f06c7473 Don't touch code that we brought in from other sources
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247 memcpy(pivot,first,size); \
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248 memmove(test+size,test,first-test); \
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249 memcpy(test,pivot,size); \
1330
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250 } \
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251 }
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252
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253 #define SWAP_nonaligned(a,b) { \
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254 register char *aa=(a),*bb=(b); \
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255 register size_t sz=size; \
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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diff changeset
256 do { register char t=*aa; *aa++=*bb; *bb++=t; } while (--sz); }
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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257
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258 #define SWAP_aligned(a,b) { \
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259 register int *aa=(int*)(a),*bb=(int*)(b); \
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260 register size_t sz=size; \
450721ad5436 It's now possible to build SDL without any C runtime at all on Windows,
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diff changeset
261 do { register int t=*aa;*aa++=*bb; *bb++=t; } while (sz-=WORD_BYTES); }
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262
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263 #define SWAP_words(a,b) { \
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diff changeset
264 register int t=*((int*)a); *((int*)a)=*((int*)b); *((int*)b)=t; }
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diff changeset
265
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diff changeset
266 /* ---------------------------------------------------------------------- */
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diff changeset
267
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diff changeset
268 static char *
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diff changeset
269 pivot_big(char *first, char *mid, char *last, size_t size,
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270 int compare(const void *, const void *))
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271 {
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272 size_t d = (((last - first) / size) >> 3) * size;
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273 char *m1, *m2, *m3;
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diff changeset
274 {
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diff changeset
275 char *a = first, *b = first + d, *c = first + 2 * d;
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276 #ifdef DEBUG_QSORT
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277 fprintf(stderr, "< %d %d %d\n", *(int *) a, *(int *) b, *(int *) c);
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278 #endif
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279 m1 = compare(a, b) < 0 ?
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280 (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
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281 : (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
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282 }
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
283 {
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
284 char *a = mid - d, *b = mid, *c = mid + d;
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285 #ifdef DEBUG_QSORT
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286 fprintf(stderr, ". %d %d %d\n", *(int *) a, *(int *) b, *(int *) c);
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287 #endif
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diff changeset
288 m2 = compare(a, b) < 0 ?
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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289 (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
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290 : (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
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291 }
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
292 {
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
293 char *a = last - 2 * d, *b = last - d, *c = last;
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294 #ifdef DEBUG_QSORT
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295 fprintf(stderr, "> %d %d %d\n", *(int *) a, *(int *) b, *(int *) c);
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296 #endif
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297 m3 = compare(a, b) < 0 ?
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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298 (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a))
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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299 : (compare(a, c) < 0 ? a : (compare(b, c) < 0 ? c : b));
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300 }
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301 #ifdef DEBUG_QSORT
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302 fprintf(stderr, "-> %d %d %d\n", *(int *) m1, *(int *) m2, *(int *) m3);
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303 #endif
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304 return compare(m1, m2) < 0 ?
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305 (compare(m2, m3) < 0 ? m2 : (compare(m1, m3) < 0 ? m3 : m1))
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306 : (compare(m1, m3) < 0 ? m1 : (compare(m2, m3) < 0 ? m3 : m2));
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307 }
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308
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309 /* ---------------------------------------------------------------------- */
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310
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311 static void
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312 qsort_nonaligned(void *base, size_t nmemb, size_t size,
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313 int (*compare) (const void *, const void *))
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314 {
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315
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316 stack_entry stack[STACK_SIZE];
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317 int stacktop = 0;
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diff changeset
318 char *first, *last;
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319 char *pivot = malloc(size);
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320 size_t trunc = TRUNC_nonaligned * size;
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321 assert(pivot != 0);
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322
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323 first = (char *) base;
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324 last = first + (nmemb - 1) * size;
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325
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326 if ((size_t) (last - first) > trunc) {
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327 char *ffirst = first, *llast = last;
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diff changeset
328 while (1) {
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329 /* Select pivot */
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
330 {
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331 char *mid = first + size * ((last - first) / size >> 1);
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332 Pivot(SWAP_nonaligned, size);
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333 memcpy(pivot, mid, size);
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334 }
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diff changeset
335 /* Partition. */
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336 Partition(SWAP_nonaligned, size);
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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337 /* Prepare to recurse/iterate. */
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338 Recurse(trunc)}
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339 }
1895
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340 PreInsertion(SWAP_nonaligned, TRUNC_nonaligned, size);
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341 Insertion(SWAP_nonaligned);
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342 free(pivot);
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343 }
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344
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345 static void
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346 qsort_aligned(void *base, size_t nmemb, size_t size,
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347 int (*compare) (const void *, const void *))
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348 {
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349
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350 stack_entry stack[STACK_SIZE];
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351 int stacktop = 0;
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diff changeset
352 char *first, *last;
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353 char *pivot = malloc(size);
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354 size_t trunc = TRUNC_aligned * size;
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355 assert(pivot != 0);
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diff changeset
356
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357 first = (char *) base;
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358 last = first + (nmemb - 1) * size;
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359
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360 if ((size_t) (last - first) > trunc) {
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361 char *ffirst = first, *llast = last;
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
362 while (1) {
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
363 /* Select pivot */
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
364 {
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diff changeset
365 char *mid = first + size * ((last - first) / size >> 1);
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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366 Pivot(SWAP_aligned, size);
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367 memcpy(pivot, mid, size);
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diff changeset
368 }
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diff changeset
369 /* Partition. */
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diff changeset
370 Partition(SWAP_aligned, size);
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diff changeset
371 /* Prepare to recurse/iterate. */
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
372 Recurse(trunc)}
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373 }
1895
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diff changeset
374 PreInsertion(SWAP_aligned, TRUNC_aligned, size);
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
375 Insertion(SWAP_aligned);
c121d94672cb SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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diff changeset
376 free(pivot);
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diff changeset
377 }
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diff changeset
378
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diff changeset
379 static void
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diff changeset
380 qsort_words(void *base, size_t nmemb,
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diff changeset
381 int (*compare) (const void *, const void *))
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diff changeset
382 {
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383
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384 stack_entry stack[STACK_SIZE];
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385 int stacktop = 0;
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386 char *first, *last;
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387 char *pivot = malloc(WORD_BYTES);
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388 assert(pivot != 0);
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389
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390 first = (char *) base;
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391 last = first + (nmemb - 1) * WORD_BYTES;
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392
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393 if (last - first > TRUNC_words) {
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394 char *ffirst = first, *llast = last;
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395 while (1) {
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396 #ifdef DEBUG_QSORT
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397 fprintf(stderr, "Doing %d:%d: ",
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398 (first - (char *) base) / WORD_BYTES,
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399 (last - (char *) base) / WORD_BYTES);
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400 #endif
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401 /* Select pivot */
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402 {
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403 char *mid =
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404 first + WORD_BYTES * ((last - first) / (2 * WORD_BYTES));
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405 Pivot(SWAP_words, WORD_BYTES);
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406 *(int *) pivot = *(int *) mid;
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407 }
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408 #ifdef DEBUG_QSORT
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409 fprintf(stderr, "pivot=%d\n", *(int *) pivot);
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410 #endif
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411 /* Partition. */
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412 Partition(SWAP_words, WORD_BYTES);
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413 /* Prepare to recurse/iterate. */
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414 Recurse(TRUNC_words)}
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415 }
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416 PreInsertion(SWAP_words, (TRUNC_words / WORD_BYTES), WORD_BYTES);
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417 /* Now do insertion sort. */
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418 last = ((char *) base) + nmemb * WORD_BYTES;
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419 for (first = ((char *) base) + WORD_BYTES; first != last;
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420 first += WORD_BYTES) {
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421 /* Find the right place for |first|. My apologies for var reuse */
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422 int *pl = (int *) (first - WORD_BYTES), *pr = (int *) first;
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423 *(int *) pivot = *(int *) first;
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424 for (; compare(pl, pivot) > 0; pr = pl, --pl) {
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425 *pr = *pl;
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426 }
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427 if (pr != (int *) first)
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428 *pr = *(int *) pivot;
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429 }
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430 free(pivot);
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431 }
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432
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433 /* ---------------------------------------------------------------------- */
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434
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435 void
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436 qsort(void *base, size_t nmemb, size_t size,
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437 int (*compare) (const void *, const void *))
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438 {
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439
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440 if (nmemb <= 1)
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441 return;
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442 if (((uintptr_t) base | size) & (WORD_BYTES - 1))
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443 qsort_nonaligned(base, nmemb, size, compare);
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444 else if (size != WORD_BYTES)
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445 qsort_aligned(base, nmemb, size, compare);
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446 else
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447 qsort_words(base, nmemb, compare);
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448 }
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449
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450 #endif /* !HAVE_QSORT */
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451 /* vi: set ts=4 sw=4 expandtab: */