find first set in file

ffs_in_file.c

#include<stdio.h>

int main(int argc, char *argv[]) {
    printf("Start reading...\n");

    FILE *fp = fopen(argv[1], "r");
    int res = 0, buff = 0, ffs = 0, pos = 0;

    while (fread(&buff, sizeof(int), 1, fp) == 1) {
        ffs = __builtin_ffs(buff);
        if (ffs > 0) {
            printf("ffs at %d\n", pos+ffs);
            break;
        }
        pos += sizeof(int);
    }

    printf("Scanned %d bytes\n", pos);
    return 0;
}