#include <stdio.h>
#include <string.h>

/*
 * This program expects the hexadecimal block hash of a Bitcoin
 * block as a argument. This information is seen with bitcoind.
 *
 * bitcoind getblockhash <block-number>
 */

#define HEXDIGITS	5
#define LOWVAL		1
#define HIGHVAL		429535 

int main(int argc, char *argv[])
{
	unsigned long val;
	char *p;

	if (argc != 2) {
		fprintf(stderr, "usage: %s <block-hash>\n", argv[0]);
		return 1;
	}

	/* start with trailing hex digits of block-hash */
	p = argv[1] + strlen(argv[1]) - HEXDIGITS;

	while (1) {
		if (p < argv[1]) {
			fprintf(stderr, "error: no value found\n");
			return 1;
		}

		if (sscanf(p, "%lx", &val) != 1) {
			fprintf(stderr, "error: invalid block-hash\n");
			return 1;
		}

		/* check value is acceptable */
		if (val >= LOWVAL && val <= HIGHVAL)
			break;

		/* move back 1 hex digit and try again */
		p--;
		*(p + HEXDIGITS) = 0;
	}

	printf("value: %lu (0x%lx)\n", val, val);

	return 0;
}