bsearch

/* Copyright 1996 Acorn Computers Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/* bsearch.c: extraced from sort.c   */
/* Copyright (C) Codemist Ltd., 1988 */

#include <stddef.h>
#include <stdlib.h>

#define Compar_(a, b) (compar(a, b))

void *__bsearch(const void *key, const void *base,
              size_t nmemb, size_t size,
              int (*compar)(const void *, const void *))
{
/* Binary search for given key in a sorted array (starting at base).     */
/* Comparisons are performed using the given function, and the array has */
/* nmemb items in it, each of size bytes.                                */
    int midn, c;
    void *midp;
    for (;;)
    {   if (nmemb==0) return NULL;      /* not found at all.             */
        else if (nmemb==1)
/* If there is only one item left in the array it is the only one that   */
/* needs to be looked at.                                                */
        {   if (Compar_(key, base)==0) return (void *)base;
            else return NULL;
        }
        midn = nmemb>>1;                /* index of middle item          */
/* I have to cast bast to (char *) here so that the addition will be     */
/* performed using natural machine arithmetic.                           */
        midp = (char *)base + midn * size;
        c = Compar_(key, midp);
        if (c==0) return midp;          /* item found (by accident)      */
        else if (c<0) nmemb = midn;     /* key is to left of midpoint    */
        else                            /* key is to the right           */
        {   base = (char *)midp + size; /* exclude the midpoint          */
            nmemb = nmemb - midn - 1;
        }
        continue;
    }
}

/* end of bsearch.c */