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1 /*
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2 * Copyright (c) 1990 Regents of the University of California.
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3 * All rights reserved.
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4 *
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5 * Redistribution and use in source and binary forms, with or without
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6 * modification, are permitted provided that the following conditions
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7 * are met:
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8 * 1. Redistributions of source code must retain the above copyright
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9 * notice, this list of conditions and the following disclaimer.
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10 * 2. Redistributions in binary form must reproduce the above copyright
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11 * notice, this list of conditions and the following disclaimer in the
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12 * documentation and/or other materials provided with the distribution.
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13 * 3. [rescinded 22 July 1999]
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14 * 4. Neither the name of the University nor the names of its contributors
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15 * may be used to endorse or promote products derived from this software
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16 * without specific prior written permission.
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17 *
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18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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28 * SUCH DAMAGE.
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29 */
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30
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31 /*
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32
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33 @deftypefn Supplemental void* bsearch (const void *@var{key}, const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, int (*@var{compar})(const void *, const void *))
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34
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35 Performs a search over an array of @var{nmemb} elements pointed to by
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36 @var{base} for a member that matches the object pointed to by @var{key}.
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37 The size of each member is specified by @var{size}. The array contents
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38 should be sorted in ascending order according to the @var{compar}
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39 comparison function. This routine should take two arguments pointing to
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40 the @var{key} and to an array member, in that order, and should return an
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41 integer less than, equal to, or greater than zero if the @var{key} object
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42 is respectively less than, matching, or greater than the array member.
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43
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44 @end deftypefn
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45
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46 */
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47
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48 #include "config.h"
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49 #include "ansidecl.h"
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50 #include <sys/types.h> /* size_t */
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51 #include <stdio.h>
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52
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53 /*
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54 * Perform a binary search.
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55 *
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56 * The code below is a bit sneaky. After a comparison fails, we
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57 * divide the work in half by moving either left or right. If lim
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58 * is odd, moving left simply involves halving lim: e.g., when lim
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59 * is 5 we look at item 2, so we change lim to 2 so that we will
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60 * look at items 0 & 1. If lim is even, the same applies. If lim
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61 * is odd, moving right again involes halving lim, this time moving
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62 * the base up one item past p: e.g., when lim is 5 we change base
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63 * to item 3 and make lim 2 so that we will look at items 3 and 4.
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64 * If lim is even, however, we have to shrink it by one before
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65 * halving: e.g., when lim is 4, we still looked at item 2, so we
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66 * have to make lim 3, then halve, obtaining 1, so that we will only
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67 * look at item 3.
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68 */
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69 void *
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70 bsearch (register const void *key, const void *base0,
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71 size_t nmemb, register size_t size,
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72 register int (*compar)(const void *, const void *))
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73 {
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74 register const char *base = (const char *) base0;
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75 register int lim, cmp;
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76 register const void *p;
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77
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78 for (lim = nmemb; lim != 0; lim >>= 1) {
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79 p = base + (lim >> 1) * size;
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80 cmp = (*compar)(key, p);
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81 if (cmp == 0)
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82 return (void *)p;
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83 if (cmp > 0) { /* key > p: move right */
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84 base = (const char *)p + size;
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85 lim--;
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86 } /* else move left */
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87 }
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88 return (NULL);
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89 }
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