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| 4973 | right-hear | 1 | /* Copyright (C) 1994 DJ Delorie, see COPYING.DJ for details */ |
| 2 | #include |
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| 3 | |||
| 4 | /*- |
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| 5 | * Copyright (c) 1980, 1983 The Regents of the University of California. |
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| 6 | * All rights reserved. |
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| 7 | * |
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| 8 | * Redistribution and use in source and binary forms are permitted |
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| 9 | * provided that: (1) source distributions retain this entire copyright |
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| 10 | * notice and comment, and (2) distributions including binaries display |
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| 11 | * the following acknowledgement: ``This product includes software |
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| 12 | * developed by the University of California, Berkeley and its contributors'' |
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| 13 | * in the documentation or other materials provided with the distribution |
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| 14 | * and in all advertising materials mentioning features or use of this |
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| 15 | * software. Neither the name of the University nor the names of its |
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| 16 | * contributors may be used to endorse or promote products derived |
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| 17 | * from this software without specific prior written permission. |
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| 18 | * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR |
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| 19 | * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED |
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| 20 | * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
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| 21 | */ |
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| 22 | |||
| 23 | /* |
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| 24 | * qsort.c: |
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| 25 | * Our own version of the system qsort routine which is faster by an average |
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| 26 | * of 25%, with lows and highs of 10% and 50%. |
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| 27 | * The THRESHold below is the insertion sort threshold, and has been adjusted |
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| 28 | * for records of size 48 bytes. |
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| 29 | * The MTHREShold is where we stop finding a better median. |
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| 30 | */ |
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| 31 | |||
| 32 | #define THRESH 4 /* threshold for insertion */ |
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| 33 | #define MTHRESH 6 /* threshold for median */ |
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| 34 | |||
| 35 | static int (*qcmp)(const void *, const void *); /* the comparison routine */ |
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| 36 | static int qsz; /* size of each record */ |
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| 37 | static int thresh; /* THRESHold in chars */ |
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| 38 | static int mthresh; /* MTHRESHold in chars */ |
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| 39 | |||
| 40 | /* |
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| 41 | * qst: |
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| 42 | * Do a quicksort |
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| 43 | * First, find the median element, and put that one in the first place as the |
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| 44 | * discriminator. (This "median" is just the median of the first, last and |
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| 45 | * middle elements). (Using this median instead of the first element is a big |
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| 46 | * win). Then, the usual partitioning/swapping, followed by moving the |
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| 47 | * discriminator into the right place. Then, figure out the sizes of the two |
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| 48 | * partions, do the smaller one recursively and the larger one via a repeat of |
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| 49 | * this code. Stopping when there are less than THRESH elements in a partition |
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| 50 | * and cleaning up with an insertion sort (in our caller) is a huge win. |
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| 51 | * All data swaps are done in-line, which is space-losing but time-saving. |
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| 52 | * (And there are only three places where this is done). |
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| 53 | */ |
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| 54 | |||
| 55 | static void |
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| 56 | qst(char *base, char *max) |
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| 57 | { |
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| 58 | char c, *i, *j, *jj; |
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| 59 | int ii; |
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| 60 | char *mid, *tmp; |
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| 61 | int lo, hi; |
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| 62 | |||
| 63 | /* |
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| 64 | * At the top here, lo is the number of characters of elements in the |
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| 65 | * current partition. (Which should be max - base). |
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| 66 | * Find the median of the first, last, and middle element and make |
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| 67 | * that the middle element. Set j to largest of first and middle. |
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| 68 | * If max is larger than that guy, then it's that guy, else compare |
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| 69 | * max with loser of first and take larger. Things are set up to |
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| 70 | * prefer the middle, then the first in case of ties. |
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| 71 | */ |
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| 72 | lo = max - base; /* number of elements as chars */ |
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| 73 | do { |
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| 74 | mid = i = base + qsz * ((lo / qsz) >> 1); |
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| 75 | if (lo >= mthresh) |
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| 76 | { |
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| 77 | j = (qcmp((jj = base), i) > 0 ? jj : i); |
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| 78 | if (qcmp(j, (tmp = max - qsz)) > 0) |
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| 79 | { |
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| 80 | /* switch to first loser */ |
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| 81 | j = (j == jj ? i : jj); |
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| 82 | if (qcmp(j, tmp) < 0) |
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| 83 | j = tmp; |
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| 84 | } |
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| 85 | if (j != i) |
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| 86 | { |
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| 87 | ii = qsz; |
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| 88 | do { |
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| 89 | c = *i; |
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| 90 | *i++ = *j; |
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| 91 | *j++ = c; |
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| 92 | } while (--ii); |
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| 93 | } |
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| 94 | } |
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| 95 | /* |
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| 96 | * Semi-standard quicksort partitioning/swapping |
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| 97 | */ |
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| 98 | for (i = base, j = max - qsz; ; ) |
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| 99 | { |
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| 100 | while (i < mid && qcmp(i, mid) <= 0) |
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| 101 | i += qsz; |
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| 102 | while (j > mid) |
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| 103 | { |
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| 104 | if (qcmp(mid, j) <= 0) |
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| 105 | { |
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| 106 | j -= qsz; |
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| 107 | continue; |
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| 108 | } |
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| 109 | tmp = i + qsz; /* value of i after swap */ |
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| 110 | if (i == mid) |
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| 111 | { |
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| 112 | /* j <-> mid, new mid is j */ |
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| 113 | mid = jj = j; |
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| 114 | } |
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| 115 | else |
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| 116 | { |
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| 117 | /* i <-> j */ |
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| 118 | jj = j; |
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| 119 | j -= qsz; |
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| 120 | } |
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| 121 | goto swap; |
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| 122 | } |
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| 123 | if (i == mid) |
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| 124 | { |
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| 125 | break; |
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| 126 | } |
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| 127 | else |
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| 128 | { |
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| 129 | /* i <-> mid, new mid is i */ |
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| 130 | jj = mid; |
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| 131 | tmp = mid = i; /* value of i after swap */ |
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| 132 | j -= qsz; |
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| 133 | } |
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| 134 | swap: |
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| 135 | ii = qsz; |
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| 136 | do { |
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| 137 | c = *i; |
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| 138 | *i++ = *jj; |
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| 139 | *jj++ = c; |
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| 140 | } while (--ii); |
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| 141 | i = tmp; |
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| 142 | } |
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| 143 | /* |
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| 144 | * Look at sizes of the two partitions, do the smaller |
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| 145 | * one first by recursion, then do the larger one by |
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| 146 | * making sure lo is its size, base and max are update |
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| 147 | * correctly, and branching back. But only repeat |
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| 148 | * (recursively or by branching) if the partition is |
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| 149 | * of at least size THRESH. |
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| 150 | */ |
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| 151 | i = (j = mid) + qsz; |
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| 152 | if ((lo = j - base) <= (hi = max - i)) |
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| 153 | { |
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| 154 | if (lo >= thresh) |
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| 155 | qst(base, j); |
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| 156 | base = i; |
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| 157 | lo = hi; |
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| 158 | } |
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| 159 | else |
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| 160 | { |
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| 161 | if (hi >= thresh) |
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| 162 | qst(i, max); |
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| 163 | max = j; |
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| 164 | } |
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| 165 | } while (lo >= thresh); |
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| 166 | } |
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| 167 | |||
| 168 | /* |
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| 169 | * qsort: |
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| 170 | * First, set up some global parameters for qst to share. Then, quicksort |
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| 171 | * with qst(), and then a cleanup insertion sort ourselves. Sound simple? |
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| 172 | * It's not... |
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| 173 | */ |
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| 174 | |||
| 175 | void |
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| 176 | qsort(void *base0, size_t n, size_t size, int (*compar)(const void *, const void *)) |
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| 177 | { |
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| 178 | char *base = (char *)base0; |
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| 179 | char c, *i, *j, *lo, *hi; |
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| 180 | char *min, *max; |
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| 181 | |||
| 182 | if (n <= 1) |
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| 183 | return; |
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| 184 | qsz = size; |
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| 185 | qcmp = compar; |
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| 186 | thresh = qsz * THRESH; |
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| 187 | mthresh = qsz * MTHRESH; |
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| 188 | max = base + n * qsz; |
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| 189 | if (n >= THRESH) |
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| 190 | { |
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| 191 | qst(base, max); |
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| 192 | hi = base + thresh; |
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| 193 | } |
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| 194 | else |
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| 195 | { |
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| 196 | hi = max; |
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| 197 | } |
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| 198 | /* |
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| 199 | * First put smallest element, which must be in the first THRESH, in |
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| 200 | * the first position as a sentinel. This is done just by searching |
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| 201 | * the first THRESH elements (or the first n if n < THRESH), finding |
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| 202 | * the min, and swapping it into the first position. |
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| 203 | */ |
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| 204 | for (j = lo = base; (lo += qsz) < hi; ) |
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| 205 | if (qcmp(j, lo) > 0) |
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| 206 | j = lo; |
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| 207 | if (j != base) |
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| 208 | { |
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| 209 | /* swap j into place */ |
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| 210 | for (i = base, hi = base + qsz; i < hi; ) |
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| 211 | { |
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| 212 | c = *j; |
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| 213 | *j++ = *i; |
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| 214 | *i++ = c; |
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| 215 | } |
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| 216 | } |
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| 217 | /* |
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| 218 | * With our sentinel in place, we now run the following hyper-fast |
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| 219 | * insertion sort. For each remaining element, min, from [1] to [n-1], |
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| 220 | * set hi to the index of the element AFTER which this one goes. |
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| 221 | * Then, do the standard insertion sort shift on a character at a time |
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| 222 | * basis for each element in the frob. |
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| 223 | */ |
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| 224 | for (min = base; (hi = min += qsz) < max; ) |
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| 225 | { |
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| 226 | while (qcmp(hi -= qsz, min) > 0) |
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| 227 | /* void */; |
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| 228 | if ((hi += qsz) != min) { |
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| 229 | for (lo = min + qsz; --lo >= min; ) |
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| 230 | { |
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| 231 | c = *lo; |
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| 232 | for (i = j = lo; (j -= qsz) >= hi; i = j) |
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| 233 | *i = *j; |
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| 234 | *i = c; |
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| 235 | } |
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| 236 | } |
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| 237 | } |
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| 238 | } |