From 881972b2a5cecdf68f9a766632999dddfb4df5a0 Mon Sep 17 00:00:00 2001 From: Igor Aleksanov <12111581+popzxc@users.noreply.github.com> Date: Mon, 28 May 2018 21:41:07 +0300 Subject: [PATCH] Fix multiplication for uint256 (#88) --- src/util/uint.rs | 47 +++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 43 insertions(+), 4 deletions(-) diff --git a/src/util/uint.rs b/src/util/uint.rs index 6b7bbd81..c6b5650c 100644 --- a/src/util/uint.rs +++ b/src/util/uint.rs @@ -61,12 +61,17 @@ macro_rules! construct_uint { let mut carry = [0u64; $n_words]; let mut ret = [0u64; $n_words]; for i in 0..$n_words { + let not_last_word = i < $n_words - 1; let upper = other as u64 * (arr[i] >> 32); let lower = other as u64 * (arr[i] & 0xFFFFFFFF); - if i < 3 { + if not_last_word { carry[i + 1] += upper >> 32; } - ret[i] = lower + (upper << 32); + let (sum, overflow) = lower.overflowing_add(upper << 32); + ret[i] = sum; + if overflow && not_last_word { + carry[i + 1] += 1; + } } $name(ret) + $name(carry) } @@ -118,10 +123,11 @@ macro_rules! construct_uint { type Output = $name; fn mul(self, other: $name) -> $name { - let mut me = self; + let mut me = $name::zero(); // TODO: be more efficient about this for i in 0..(2 * $n_words) { - me = (me + me.mul_u32((other >> (32 * i)).low_u32())) << (32 * i); + let to_mul = (other >> (32 * i)).low_u32(); + me = me + (self.mul_u32(to_mul) << (32 * i)); } me } @@ -468,6 +474,39 @@ mod tests { // TODO: bit inversion } + #[test] + pub fn mul_u32_test() { + let u64_val = Uint256::from_u64(0xDEADBEEFDEADBEEF).unwrap(); + + let u96_res = u64_val.mul_u32(0xFFFFFFFF); + let u128_res = u96_res.mul_u32(0xFFFFFFFF); + let u160_res = u128_res.mul_u32(0xFFFFFFFF); + let u192_res = u160_res.mul_u32(0xFFFFFFFF); + let u224_res = u192_res.mul_u32(0xFFFFFFFF); + let u256_res = u224_res.mul_u32(0xFFFFFFFF); + + assert_eq!(u96_res, Uint256([0xffffffff21524111u64, 0xDEADBEEE, 0, 0])); + assert_eq!(u128_res, Uint256([0x21524111DEADBEEFu64, 0xDEADBEEE21524110, 0, 0])); + assert_eq!(u160_res, Uint256([0xBD5B7DDD21524111u64, 0x42A4822200000001, 0xDEADBEED, 0])); + assert_eq!(u192_res, Uint256([0x63F6C333DEADBEEFu64, 0xBD5B7DDFBD5B7DDB, 0xDEADBEEC63F6C334, 0])); + assert_eq!(u224_res, Uint256([0x7AB6FBBB21524111u64, 0xFFFFFFFBA69B4558, 0x854904485964BAAA, 0xDEADBEEB])); + assert_eq!(u256_res, Uint256([0xA69B4555DEADBEEFu64, 0xA69B455CD41BB662, 0xD41BB662A69B4550, 0xDEADBEEAA69B455C])); + } + + #[test] + pub fn multiplication_test() { + let u64_val = Uint256::from_u64(0xDEADBEEFDEADBEEF).unwrap(); + + let u128_res = u64_val * u64_val; + + assert_eq!(u128_res, Uint256([0x048D1354216DA321u64, 0xC1B1CD13A4D13D46, 0, 0])); + + let u256_res = u128_res * u128_res; + + assert_eq!(u256_res, Uint256([0xF4E166AAD40D0A41u64, 0xF5CF7F3618C2C886u64, + 0x4AFCFF6F0375C608u64, 0x928D92B4D7F5DF33u64])); + } + #[test] pub fn uint256_bitslice_test() { let init = Uint256::from_u64(0xDEADBEEFDEADBEEF).unwrap();