mult.c

/*****************************************************************************/

static unsigned __int128 decode_number128(unsigned char* input, uint len) {
	uint i;
	unsigned __int128 result;
	result = 0;
	for(i = 0 ; i < len ; i++) {
		result = result << 8;
		result += (unsigned char)input[i];
	}

	return result;
}

/*****************************************************************************/

static int check_pow(unsigned char* difficulty, uint difficulty_len, unsigned char* ethash) {
	unsigned __int128 difficulty_value = decode_number128(difficulty, difficulty_len);
	unsigned __int128 ethash_value[4];
	unsigned __int128 result[4];	
	unsigned __int128 max_uint64 = 0xFFFFFFFFFFFFFFFFL;
	unsigned __int128 temp;
	unsigned __int128 temp2;

	uint i;

	if(difficulty_len >= 8) printf("error: unexpected difficulty len\n");
	memset(result, 0x00, sizeof(result));

	for(i = 0 ; i < 4; i++) ethash_value[i] = decode_number128(ethash + 8*i, 8);

	temp = difficulty_value * ethash_value[3];
	result[3] = temp & max_uint64;
	result[2] = temp >> 64;

	temp = difficulty_value * ethash_value[2];
	temp2 = (temp & max_uint64) + result[2];
	result[2] = temp2 & max_uint64;
	result[1] = (temp2 >> 64) + (temp >> 64);

	temp = difficulty_value * ethash_value[1];
	temp2 = (temp & max_uint64) + result[1];
	result[1] = temp2 & max_uint64;
	result[0] = (temp2 >> 64) + (temp >> 64);;

	temp = difficulty_value * ethash_value[0];
	temp2 = (temp & max_uint64) + result[0];
	result[0] = temp2 & max_uint64;

	printf("0x%016lx%016lx%016lx%016lx\n", (long unsigned int)result[0] , (long unsigned int)result[1], (long unsigned int)result[2], (long unsigned int)result[3]);
	
	return ((temp2 >> 64) + (temp >> 64)) == 0;
}