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fix(u256): align with rust for shift behaviours

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tmontaigu
2023-06-02 09:55:28 +02:00
parent 71209e3927
commit 4947eefad4
1 changed files with 22 additions and 6 deletions
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28
tfhe/src/integer/u256.rs
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@@ -163,9 +163,7 @@ impl std::ops::Sub<Self> for U256 {
impl std::ops::ShrAssign<u32> for U256 {
// move bits from MSB to LSB
fn shr_assign(&mut self, shift: u32) {
if shift > 256 {
self.0.as_mut_slice().fill(0);
}
let shift = shift % Self::BITS;
let num_rotations = (shift / u64::BITS) as usize;
self.0.rotate_left(num_rotations);
@@ -203,9 +201,7 @@ impl std::ops::Shr<u32> for U256 {
impl std::ops::ShlAssign<u32> for U256 {
// move bits from LSB to MSB
fn shl_assign(&mut self, shift: u32) {
if shift > 256 {
self.0.as_mut_slice().fill(0);
}
let shift = shift % Self::BITS;
let num_rotations = (shift / u64::BITS) as usize;
self.0.rotate_right(num_rotations);
@@ -355,6 +351,26 @@ mod tests {
assert_eq!(!u128::MIN, u128::MAX);
}
#[test]
fn test_shl_limits() {
assert_eq!(U256::ONE << 256, U256::ONE << (256 % U256::BITS));
assert_eq!(U256::ONE << 257, U256::ONE << (257 % U256::BITS));
// We aim to have same behaviour as rust native types
assert_eq!(1u128.wrapping_shl(128), 1u128 << (128 % u128::BITS));
assert_eq!(1u128.wrapping_shl(129), 1u128 << (129 % u128::BITS));
}
#[test]
fn test_shr_limits() {
assert_eq!(U256::MAX >> 256, U256::MAX >> (256 % U256::BITS));
assert_eq!(U256::MAX >> 257, U256::MAX >> (257 % U256::BITS));
// We aim to have same behaviour as rust native types
assert_eq!(u128::MAX.wrapping_shr(128), u128::MAX >> (128 % u128::BITS));
assert_eq!(u128::MAX.wrapping_shr(129), u128::MAX >> (129 % u128::BITS));
}
#[test]
fn test_shr() {
assert_eq!(U256::MAX >> 128, U256::from(u128::MAX));