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Annotation of 43BSDReno/lib/libc/stdlib/bsearch.c, revision 1.1.1.1

1.1       root        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 are permitted
                      6:  * provided that: (1) source distributions retain this entire copyright
                      7:  * notice and comment, and (2) distributions including binaries display
                      8:  * the following acknowledgement:  ``This product includes software
                      9:  * developed by the University of California, Berkeley and its contributors''
                     10:  * in the documentation or other materials provided with the distribution
                     11:  * and in all advertising materials mentioning features or use of this
                     12:  * software. Neither the name of the University nor the names of its
                     13:  * contributors may be used to endorse or promote products derived
                     14:  * from this software without specific prior written permission.
                     15:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
                     16:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
                     17:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
                     18:  */
                     19: 
                     20: #if defined(LIBC_SCCS) && !defined(lint)
                     21: static char sccsid[] = "@(#)bsearch.c  5.3 (Berkeley) 5/17/90";
                     22: #endif /* LIBC_SCCS and not lint */
                     23: 
                     24: #include <stddef.h>            /* size_t */
                     25: #include <stdlib.h>
                     26: 
                     27: /*
                     28:  * Perform a binary search.
                     29:  *
                     30:  * The code below is a bit sneaky.  After a comparison fails, we
                     31:  * divide the work in half by moving either left or right. If lim
                     32:  * is odd, moving left simply involves halving lim: e.g., when lim
                     33:  * is 5 we look at item 2, so we change lim to 2 so that we will
                     34:  * look at items 0 & 1.  If lim is even, the same applies.  If lim
                     35:  * is odd, moving right again involes halving lim, this time moving
                     36:  * the base up one item past p: e.g., when lim is 5 we change base
                     37:  * to item 3 and make lim 2 so that we will look at items 3 and 4.
                     38:  * If lim is even, however, we have to shrink it by one before
                     39:  * halving: e.g., when lim is 4, we still looked at item 2, so we
                     40:  * have to make lim 3, then halve, obtaining 1, so that we will only
                     41:  * look at item 3.
                     42:  */
                     43: void *
                     44: bsearch(key, base0, nmemb, size, compar)
                     45:        register void *key;
                     46:        void *base0;
                     47:        size_t nmemb;
                     48:        register size_t size;
                     49:        register int (*compar)();
                     50: {
                     51:        register char *base = base0;
                     52:        register int lim, cmp;
                     53:        register void *p;
                     54: 
                     55:        for (lim = nmemb; lim != 0; lim >>= 1) {
                     56:                p = base + (lim >> 1) * size;
                     57:                cmp = (*compar)(key, p);
                     58:                if (cmp == 0)
                     59:                        return (p);
                     60:                if (cmp > 0) {  /* key > p: move right */
                     61:                        base = (char *)p + size;
                     62:                        lim--;
                     63:                } /* else move left */
                     64:        }
                     65:        return (NULL);
                     66: }

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