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1 /* Plug-compatible replacement for UNIX qsort.
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2 Copyright (C) 1989 Free Software Foundation, Inc.
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3 Written by Douglas C. Schmidt (schmidt@ics.uci.edu)
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4
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5 This file is part of GNU CC.
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6
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7 GNU QSORT is free software; you can redistribute it and/or modify
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8 it under the terms of the GNU General Public License as published by
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9 the Free Software Foundation; either version 2, or (at your option)
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10 any later version.
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11
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12 GNU QSORT is distributed in the hope that it will be useful,
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13 but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 GNU General Public License for more details.
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16
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17 You should have received a copy of the GNU General Public License
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18 along with GNU QSORT; see the file COPYING. If not, write to
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19 the Free the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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20 Boston, MA 02111-1307, USA. */
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21
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22 /* Synched up with: FSF 19.28. */
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23
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24 #ifdef sparc
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25 #include <alloca.h>
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26 #endif
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27
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28 /* Invoke the comparison function, returns either 0, < 0, or > 0. */
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29 #define CMP(A,B) ((*cmp)((A),(B)))
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30
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31 /* Byte-wise swap two items of size SIZE. */
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32 #define SWAP(A,B,SIZE) do {int sz = (SIZE); char *a = (A); char *b = (B); \
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33 do { char _temp = *a;*a++ = *b;*b++ = _temp;} while (--sz);} while (0)
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34
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35 /* Copy SIZE bytes from item B to item A. */
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36 #define COPY(A,B,SIZE) {int sz = (SIZE); do { *(A)++ = *(B)++; } while (--sz); }
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37
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38 /* This should be replaced by a standard ANSI macro. */
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39 #define BYTES_PER_WORD 8
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40
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41 /* The next 4 #defines implement a very fast in-line stack abstraction. */
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42 #define STACK_SIZE (BYTES_PER_WORD * sizeof (long))
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43 #define PUSH(LOW,HIGH) do {top->lo = LOW;top++->hi = HIGH;} while (0)
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44 #define POP(LOW,HIGH) do {LOW = (--top)->lo;HIGH = top->hi;} while (0)
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45 #define STACK_NOT_EMPTY (stack < top)
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46
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47 /* Discontinue quicksort algorithm when partition gets below this size.
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48 This particular magic number was chosen to work best on a Sun 4/260. */
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49 #define MAX_THRESH 4
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50
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51 /* Stack node declarations used to store unfulfilled partition obligations. */
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52 typedef struct
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53 {
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54 char *lo;
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55 char *hi;
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56 } stack_node;
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57
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58 /* Order size using quicksort. This implementation incorporates
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59 four optimizations discussed in Sedgewick:
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60
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61 1. Non-recursive, using an explicit stack of pointer that store the
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62 next array partition to sort. To save time, this maximum amount
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63 of space required to store an array of MAX_INT is allocated on the
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64 stack. Assuming a 32-bit integer, this needs only 32 *
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65 sizeof (stack_node) == 136 bits. Pretty cheap, actually.
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66
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67 2. Chose the pivot element using a median-of-three decision tree.
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68 This reduces the probability of selecting a bad pivot value and
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69 eliminates certain extraneous comparisons.
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70
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71 3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
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72 insertion sort to order the MAX_THRESH items within each partition.
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73 This is a big win, since insertion sort is faster for small, mostly
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74 sorted array segments.
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75
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76 4. The larger of the two sub-partitions is always pushed onto the
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77 stack first, with the algorithm then concentrating on the
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78 smaller partition. This *guarantees* no more than log (n)
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79 stack size is needed (actually O(1) in this case)! */
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80
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81 int
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82 qsort (base_ptr, total_elems, size, cmp)
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83 char *base_ptr;
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84 int total_elems;
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85 int size;
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86 int (*cmp)();
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87 {
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88 /* Allocating SIZE bytes for a pivot buffer facilitates a better
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89 algorithm below since we can do comparisons directly on the pivot. */
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90 char *pivot_buffer = (char *) alloca (size);
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91 int max_thresh = MAX_THRESH * size;
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92
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93 if (total_elems > MAX_THRESH)
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94 {
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95 char *lo = base_ptr;
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96 char *hi = lo + size * (total_elems - 1);
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97 stack_node stack[STACK_SIZE]; /* Largest size needed for 32-bit int!!! */
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98 stack_node *top = stack + 1;
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99
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100 while (STACK_NOT_EMPTY)
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101 {
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102 char *left_ptr;
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103 char *right_ptr;
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104 {
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105 char *pivot = pivot_buffer;
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106 {
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107 /* Select median value from among LO, MID, and HI. Rearrange
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108 LO and HI so the three values are sorted. This lowers the
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109 probability of picking a pathological pivot value and
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110 skips a comparison for both the LEFT_PTR and RIGHT_PTR. */
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111
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112 char *mid = lo + size * ((hi - lo) / size >> 1);
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113
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114 if (CMP (mid, lo) < 0)
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115 SWAP (mid, lo, size);
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116 if (CMP (hi, mid) < 0)
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117 SWAP (mid, hi, size);
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118 else
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119 goto jump_over;
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120 if (CMP (mid, lo) < 0)
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121 SWAP (mid, lo, size);
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122 jump_over:
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123 COPY (pivot, mid, size);
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124 pivot = pivot_buffer;
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125 }
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126 left_ptr = lo + size;
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127 right_ptr = hi - size;
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128
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129 /* Here's the famous ``collapse the walls'' section of quicksort.
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130 Gotta like those tight inner loops! They are the main reason
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131 that this algorithm runs much faster than others. */
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132 do
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133 {
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134 while (CMP (left_ptr, pivot) < 0)
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135 left_ptr += size;
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136
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137 while (CMP (pivot, right_ptr) < 0)
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138 right_ptr -= size;
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139
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140 if (left_ptr < right_ptr)
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141 {
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142 SWAP (left_ptr, right_ptr, size);
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143 left_ptr += size;
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144 right_ptr -= size;
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145 }
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146 else if (left_ptr == right_ptr)
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147 {
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148 left_ptr += size;
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149 right_ptr -= size;
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150 break;
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151 }
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152 }
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153 while (left_ptr <= right_ptr);
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154
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155 }
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156
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157 /* Set up pointers for next iteration. First determine whether
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158 left and right partitions are below the threshold size. If so,
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159 ignore one or both. Otherwise, push the larger partition's
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160 bounds on the stack and continue sorting the smaller one. */
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161
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162 if ((right_ptr - lo) <= max_thresh)
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163 {
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164 if ((hi - left_ptr) <= max_thresh) /* Ignore both small partitions. */
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165 POP (lo, hi);
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166 else /* Ignore small left partition. */
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167 lo = left_ptr;
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168 }
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169 else if ((hi - left_ptr) <= max_thresh) /* Ignore small right partition. */
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170 hi = right_ptr;
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171 else if ((right_ptr - lo) > (hi - left_ptr)) /* Push larger left partition indices. */
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172 {
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173 PUSH (lo, right_ptr);
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174 lo = left_ptr;
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175 }
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176 else /* Push larger right partition indices. */
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177 {
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178 PUSH (left_ptr, hi);
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179 hi = right_ptr;
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180 }
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181 }
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182 }
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183
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184 /* Once the BASE_PTR array is partially sorted by quicksort the rest
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185 is completely sorted using insertion sort, since this is efficient
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186 for partitions below MAX_THRESH size. BASE_PTR points to the beginning
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187 of the array to sort, and END_PTR points at the very last element in
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188 the array (*not* one beyond it!). */
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189
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190 #define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
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191
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192 {
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193 char *end_ptr = base_ptr + size * (total_elems - 1);
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194 char *run_ptr;
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195 char *tmp_ptr = base_ptr;
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196 char *thresh = MIN (end_ptr, base_ptr + max_thresh);
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197
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198 /* Find smallest element in first threshold and place it at the
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199 array's beginning. This is the smallest array element,
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200 and the operation speeds up insertion sort's inner loop. */
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201
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202 for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
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203 if (CMP (run_ptr, tmp_ptr) < 0)
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204 tmp_ptr = run_ptr;
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205
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206 if (tmp_ptr != base_ptr)
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207 SWAP (tmp_ptr, base_ptr, size);
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208
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209 /* Insertion sort, running from left-hand-side up to `right-hand-side.'
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210 Pretty much straight out of the original GNU qsort routine. */
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211
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212 for (run_ptr = base_ptr + size; (tmp_ptr = run_ptr += size) <= end_ptr; )
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213 {
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214
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215 while (CMP (run_ptr, tmp_ptr -= size) < 0)
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216 ;
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217
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218 if ((tmp_ptr += size) != run_ptr)
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219 {
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220 char *trav;
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221
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222 for (trav = run_ptr + size; --trav >= run_ptr;)
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223 {
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224 char c = *trav;
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225 char *hi, *lo;
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226
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227 for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
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228 *hi = *lo;
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229 *hi = c;
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230 }
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231 }
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232
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233 }
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234 }
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235 return 1;
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236 }
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237
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