search.c

it is a great algorithm to secarching.

#include "search.h"

/* binarysearch() - A binary search implementation which takes the same
 * arguments as the C library function bsearch() provided by stdlib.h.  It
 * searches the sorted array at address base, which has nmemb elements, each of
 * which is size bytes long.  compar is a pointer to a comparison function.
 * The function compares two array elements, and returns a negative, zero, or
 * positive integer depending on whether the first array element is less than,
 * equal to, or greater than the second.
 */
void *binarysearch(const void *key, const void *base, size_t nmemb,
		   size_t size, int (*compar)(const void *, const void *))
{
    int min, max, mid;
    void *test;
    int c;

    min = 0;
    max = nmemb - 1;

    do {
        mid = (min + max) >> 1;
        test = base + mid * size;
	
	c = compar(key, test);
	if(c < 0) {
            max = mid - 1;
	}
        else if(c > 0) {
            min = mid + 1;
	}
	else {
            return test;
	}
	
    } while(min <= max);

    return NULL;
}