| 1 | /* |
| 2 | * Copyright (c) 1990 Regents of the University of California. |
| 3 | * All rights reserved. |
| 4 | * |
| 5 | * Redistribution and use in source and binary forms, with or without |
| 6 | * modification, are permitted provided that the following conditions |
| 7 | * are met: |
| 8 | * 1. Redistributions of source code must retain the above copyright |
| 9 | * notice, this list of conditions and the following disclaimer. |
| 10 | * 2. Redistributions in binary form must reproduce the above copyright |
| 11 | * notice, this list of conditions and the following disclaimer in the |
| 12 | * documentation and/or other materials provided with the distribution. |
| 13 | * 3. [rescinded 22 July 1999] |
| 14 | * 4. Neither the name of the University nor the names of its contributors |
| 15 | * may be used to endorse or promote products derived from this software |
| 16 | * without specific prior written permission. |
| 17 | * |
| 18 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| 19 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 20 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 21 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| 22 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| 23 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| 24 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| 25 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| 26 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| 27 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| 28 | * SUCH DAMAGE. |
| 29 | */ |
| 30 | |
| 31 | /* |
| 32 | |
| 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 *)) |
| 34 | |
| 35 | Performs a search over an array of @var{nmemb} elements pointed to by |
| 36 | @var{base} for a member that matches the object pointed to by @var{key}. |
| 37 | The size of each member is specified by @var{size}. The array contents |
| 38 | should be sorted in ascending order according to the @var{compar} |
| 39 | comparison function. This routine should take two arguments pointing to |
| 40 | the @var{key} and to an array member, in that order, and should return an |
| 41 | integer less than, equal to, or greater than zero if the @var{key} object |
| 42 | is respectively less than, matching, or greater than the array member. |
| 43 | |
| 44 | @end deftypefn |
| 45 | |
| 46 | */ |
| 47 | |
| 48 | #include "config.h" |
| 49 | #include "ansidecl.h" |
| 50 | #include <sys/types.h> /* size_t */ |
| 51 | #include <stdio.h> |
| 52 | |
| 53 | /* |
| 54 | * Perform a binary search. |
| 55 | * |
| 56 | * The code below is a bit sneaky. After a comparison fails, we |
| 57 | * divide the work in half by moving either left or right. If lim |
| 58 | * is odd, moving left simply involves halving lim: e.g., when lim |
| 59 | * is 5 we look at item 2, so we change lim to 2 so that we will |
| 60 | * look at items 0 & 1. If lim is even, the same applies. If lim |
| 61 | * is odd, moving right again involes halving lim, this time moving |
| 62 | * the base up one item past p: e.g., when lim is 5 we change base |
| 63 | * to item 3 and make lim 2 so that we will look at items 3 and 4. |
| 64 | * If lim is even, however, we have to shrink it by one before |
| 65 | * halving: e.g., when lim is 4, we still looked at item 2, so we |
| 66 | * have to make lim 3, then halve, obtaining 1, so that we will only |
| 67 | * look at item 3. |
| 68 | */ |
| 69 | void * |
| 70 | bsearch(key, base0, nmemb, size, compar) |
| 71 | register void *key; |
| 72 | void *base0; |
| 73 | size_t nmemb; |
| 74 | register size_t size; |
| 75 | register int (*compar)(); |
| 76 | { |
| 77 | register char *base = base0; |
| 78 | register int lim, cmp; |
| 79 | register void *p; |
| 80 | |
| 81 | for (lim = nmemb; lim != 0; lim >>= 1) { |
| 82 | p = base + (lim >> 1) * size; |
| 83 | cmp = (*compar)(key, p); |
| 84 | if (cmp == 0) |
| 85 | return (p); |
| 86 | if (cmp > 0) { /* key > p: move right */ |
| 87 | base = (char *)p + size; |
| 88 | lim--; |
| 89 | } /* else move left */ |
| 90 | } |
| 91 | return (NULL); |
| 92 | } |