/* Problem Forge, Problem of the Month, rungs 06 and 07: the rule.  CC0 1.0 (public domain).
   Vertices i < j are joined when the first bit of SHA-256(K, i, j) is 1,
   with K as its 32 bytes and i, j as 8-byte big-endian numbers.
   Build: cc rule.c -lcrypto      Use: ./a.out KEY i j   (prints 1 if joined, else 0) */
#include <openssl/sha.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

int joined(const unsigned char key[32], uint64_t i, uint64_t j) {
    unsigned char msg[48], out[32];
    if (i > j) { uint64_t t = i; i = j; j = t; }
    for (int b = 0; b < 32; b++) msg[b] = key[b];
    for (int b = 0; b < 8; b++) {
        msg[32 + b] = (unsigned char)(i >> (56 - 8 * b));
        msg[40 + b] = (unsigned char)(j >> (56 - 8 * b));
    }
    SHA256(msg, sizeof msg, out);
    return out[0] >> 7;
}

int main(int argc, char **argv) {
    unsigned char key[32];
    if (argc != 4) return 2;
    for (int b = 0; b < 32; b++) sscanf(argv[1] + 2 * b, "%2hhx", &key[b]);
    printf("%d\n", joined(key, strtoull(argv[2], 0, 10), strtoull(argv[3], 0, 10)));
    return 0;
}