A simple implementation of a binary search algorithm for string arrays using Amiga OS semantics. wasBinarySearch takes as parameters:

1. the string to search for,
2. the array to search in,
3. the lower-bound index to start the search from,
4. the upper-bound index to stop at

Note that the algorithm assumes that the array to be searched has been previously sorted.

wasBinarySearch.c

/*************************************************************************/
/*    Copyright (C) 2015 Wizardry and Steamworks - License: GNU GPLv3    */
/*************************************************************************/
/*                                                                       */
/*  wasBinarySearch                                                      */
/*                                                                       */
/*  An implementation of a binary search algorithm for strings.          */
/*                                                                       */
/*  Compile on Amiga OS using SAS/C: sc link wasBinarySearch.c           */
/*                                                                       */
/*************************************************************************/
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#include <proto/exec.h>
#include <proto/dos.h>
 
/*************************************************************************/
/*    Copyright (C) 2015 Wizardry and Steamworks - License: GNU GPLv3    */
/*************************************************************************/
LONG wasBinarySearch(UBYTE *e, UBYTE **a, ULONG l, ULONG r) {
    LONG m = (r + l) / 2;
    LONG x = strcmp(e, a[m]);
 
    if(x == 0) return m;
    if(l == r) return -1;
    if(x < 0) r = m - 1;
    if(x > 0) l = m + 1;
 
    return binarySearch(e, a, l, r);
}
 
int main(void) {
    UBYTE *a[10] = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j" };
    Printf("%ld\n", binarySearch("c", a, 0, 9));
}