bsearch.c

static inline int
bin_search(const void *vals, int cnt, int siz, void *val,
        int(*cmp_less)(const void *a, const void *b)) {
  int half, nleft = cnt;
  const unsigned char *base = vals;
  while ((half = (nleft >> 1)) > 0) {
    const unsigned char *mid = base + half * siz;
    base = cmp_less(mid, val) ? mid : base;
    nleft -= half;
  }
  base += (nleft == 1 && cmp_less(base, val)) ? siz : 0;
  return (base - (unsigned char*)(vals))/siz;
}


#include <stdio.h>
#include <stdlib.h>

static inline int
cmp_less(const void *a, const void *b) {
    return *(int*)a < *(int*)b;
}
extern int
main(int argc, char **argv) {
    int a[64]; 
    for ( int i = 2; i < argc; ++i) {
        a[i] = atoi(argv[i]);
    }
    int x = atoi(argv[1]);
    int elm = bin_search(a, argc-1, sizeof(int), &x, cmp_less);
    printf("%d\n", elm);
    return 0;
}