Mercurial > sdl-ios-xcode
annotate src/stdlib/SDL_qsort.c @ 2324:3202e4826c57
more valgrind errors fixed. Plus I ran make indent which changed a few files.
author | Bob Pendleton <bob@pendleton.com> |
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date | Fri, 07 Mar 2008 17:20:37 +0000 |
parents | c121d94672cb |
children | dc1eb82ffdaa |
rev | line source |
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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, |
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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 |
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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 { \ |
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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) { \ |
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244 /* Shift everything in [test,first) \ |
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245 * up by one, and place |first| \ |
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246 * where |test| is. */ \ |
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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); \ |
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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; \ |
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256 do { register char t=*aa; *aa++=*bb; *bb++=t; } while (--sz); } |
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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; \ |
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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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264 register int t=*((int*)a); *((int*)a)=*((int*)b); *((int*)b)=t; } |
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265 |
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266 /* ---------------------------------------------------------------------- */ |
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267 |
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268 static char * |
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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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274 { |
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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 } |
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283 { |
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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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288 m2 = compare(a, b) < 0 ? |
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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 } |
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292 { |
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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 ? |
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298 (compare(b, c) < 0 ? b : (compare(a, c) < 0 ? c : a)) |
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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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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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328 while (1) { |
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329 /* Select pivot */ |
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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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335 /* Partition. */ |
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336 Partition(SWAP_nonaligned, size); |
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337 /* Prepare to recurse/iterate. */ |
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338 Recurse(trunc)} |
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339 } |
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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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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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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; |
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362 while (1) { |
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363 /* Select pivot */ |
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364 { |
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365 char *mid = first + size * ((last - first) / size >> 1); |
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366 Pivot(SWAP_aligned, size); |
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367 memcpy(pivot, mid, size); |
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368 } |
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369 /* Partition. */ |
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370 Partition(SWAP_aligned, size); |
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371 /* Prepare to recurse/iterate. */ |
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372 Recurse(trunc)} |
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373 } |
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374 PreInsertion(SWAP_aligned, TRUNC_aligned, size); |
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375 Insertion(SWAP_aligned); |
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376 free(pivot); |
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377 } |
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378 |
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379 static void |
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380 qsort_words(void *base, size_t nmemb, |
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381 int (*compare) (const void *, const void *)) |
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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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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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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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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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429 } |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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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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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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436 qsort(void *base, size_t nmemb, size_t size, |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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437 int (*compare) (const void *, const void *)) |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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438 { |
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439 |
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440 if (nmemb <= 1) |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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441 return; |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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442 if (((uintptr_t) base | size) & (WORD_BYTES - 1)) |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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443 qsort_nonaligned(base, nmemb, size, compare); |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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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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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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446 else |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
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447 qsort_words(base, nmemb, compare); |
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It's now possible to build SDL without any C runtime at all on Windows,
Sam Lantinga <slouken@libsdl.org>
parents:
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448 } |
450721ad5436
It's now possible to build SDL without any C runtime at all on Windows,
Sam Lantinga <slouken@libsdl.org>
parents:
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changeset
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449 |
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A few fixes to get this building on Linux again
Sam Lantinga <slouken@libsdl.org>
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450 #endif /* !HAVE_QSORT */ |
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SDL 1.2 is moving to a branch, and SDL 1.3 is becoming the head.
Sam Lantinga <slouken@libsdl.org>
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451 /* vi: set ts=4 sw=4 expandtab: */ |