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