http://news.ycombinator.com/item?id=1923298

contains.c

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

#define mask(c) (1 << ('z' - c))
#define all (1 << (('z' - 'a') + 2)) - 1//bitmap when all the characters have been seen


int contains(char *haystack, char *needle) {
    int seen = 0; //bitmap of characters we have been seen 

    for(;*haystack;haystack++) {
        if (seen == all)
            return 1;

        seen |= mask(*haystack);
    }   

    for(;*needle; needle++)
        if (!(mask(*needle) & seen))
            return 0;

    return 1;
}