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Diffstat (limited to 'vendor/crypto-bigint/src/uint/shl.rs')
| -rw-r--r-- | vendor/crypto-bigint/src/uint/shl.rs | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/vendor/crypto-bigint/src/uint/shl.rs b/vendor/crypto-bigint/src/uint/shl.rs new file mode 100644 index 0000000..1dbc40f --- /dev/null +++ b/vendor/crypto-bigint/src/uint/shl.rs @@ -0,0 +1,216 @@ +//! [`Uint`] bitwise left shift operations. + +use crate::{CtChoice, Limb, Uint, Word}; +use core::ops::{Shl, ShlAssign}; + +impl<const LIMBS: usize> Uint<LIMBS> { + /// Computes `self << shift` where `0 <= shift < Limb::BITS`, + /// returning the result and the carry. + #[inline(always)] + pub(crate) const fn shl_limb(&self, n: usize) -> (Self, Limb) { + let mut limbs = [Limb::ZERO; LIMBS]; + + let nz = Limb(n as Word).ct_is_nonzero(); + let lshift = n as Word; + let rshift = Limb::ct_select(Limb::ZERO, Limb((Limb::BITS - n) as Word), nz).0; + let carry = Limb::ct_select( + Limb::ZERO, + Limb(self.limbs[LIMBS - 1].0.wrapping_shr(Word::BITS - n as u32)), + nz, + ); + + let mut i = LIMBS - 1; + while i > 0 { + let mut limb = self.limbs[i].0 << lshift; + let hi = self.limbs[i - 1].0 >> rshift; + limb |= nz.if_true(hi); + limbs[i] = Limb(limb); + i -= 1 + } + limbs[0] = Limb(self.limbs[0].0 << lshift); + + (Uint::<LIMBS>::new(limbs), carry) + } + + /// Computes `self << shift`. + /// + /// NOTE: this operation is variable time with respect to `n` *ONLY*. + /// + /// When used with a fixed `n`, this function is constant-time with respect + /// to `self`. + #[inline(always)] + pub const fn shl_vartime(&self, n: usize) -> Self { + let mut limbs = [Limb::ZERO; LIMBS]; + + if n >= Limb::BITS * LIMBS { + return Self { limbs }; + } + + let shift_num = n / Limb::BITS; + let rem = n % Limb::BITS; + + let mut i = LIMBS; + while i > shift_num { + i -= 1; + limbs[i] = self.limbs[i - shift_num]; + } + + let (new_lower, _carry) = (Self { limbs }).shl_limb(rem); + new_lower + } + + /// Computes a left shift on a wide input as `(lo, hi)`. + /// + /// NOTE: this operation is variable time with respect to `n` *ONLY*. + /// + /// When used with a fixed `n`, this function is constant-time with respect + /// to `self`. + #[inline(always)] + pub const fn shl_vartime_wide(lower_upper: (Self, Self), n: usize) -> (Self, Self) { + let (lower, mut upper) = lower_upper; + let new_lower = lower.shl_vartime(n); + upper = upper.shl_vartime(n); + if n >= Self::BITS { + upper = upper.bitor(&lower.shl_vartime(n - Self::BITS)); + } else { + upper = upper.bitor(&lower.shr_vartime(Self::BITS - n)); + } + + (new_lower, upper) + } + + /// Computes `self << n`. + /// Returns zero if `n >= Self::BITS`. + pub const fn shl(&self, shift: usize) -> Self { + let overflow = CtChoice::from_usize_lt(shift, Self::BITS).not(); + let shift = shift % Self::BITS; + let mut result = *self; + let mut i = 0; + while i < Self::LOG2_BITS { + let bit = CtChoice::from_lsb((shift as Word >> i) & 1); + result = Uint::ct_select(&result, &result.shl_vartime(1 << i), bit); + i += 1; + } + + Uint::ct_select(&result, &Self::ZERO, overflow) + } +} + +impl<const LIMBS: usize> Shl<usize> for Uint<LIMBS> { + type Output = Uint<LIMBS>; + + /// NOTE: this operation is variable time with respect to `rhs` *ONLY*. + /// + /// When used with a fixed `rhs`, this function is constant-time with respect + /// to `self`. + fn shl(self, rhs: usize) -> Uint<LIMBS> { + Uint::<LIMBS>::shl(&self, rhs) + } +} + +impl<const LIMBS: usize> Shl<usize> for &Uint<LIMBS> { + type Output = Uint<LIMBS>; + + /// NOTE: this operation is variable time with respect to `rhs` *ONLY*. + /// + /// When used with a fixed `rhs`, this function is constant-time with respect + /// to `self`. + fn shl(self, rhs: usize) -> Uint<LIMBS> { + self.shl(rhs) + } +} + +impl<const LIMBS: usize> ShlAssign<usize> for Uint<LIMBS> { + /// NOTE: this operation is variable time with respect to `rhs` *ONLY*. + /// + /// When used with a fixed `rhs`, this function is constant-time with respect + /// to `self`. + fn shl_assign(&mut self, rhs: usize) { + *self = self.shl(rhs) + } +} + +#[cfg(test)] +mod tests { + use crate::{Limb, Uint, U128, U256}; + + const N: U256 = + U256::from_be_hex("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141"); + + const TWO_N: U256 = + U256::from_be_hex("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFD755DB9CD5E9140777FA4BD19A06C8282"); + + const FOUR_N: U256 = + U256::from_be_hex("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFAEABB739ABD2280EEFF497A3340D90504"); + + const SIXTY_FIVE: U256 = + U256::from_be_hex("FFFFFFFFFFFFFFFD755DB9CD5E9140777FA4BD19A06C82820000000000000000"); + + const EIGHTY_EIGHT: U256 = + U256::from_be_hex("FFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD03641410000000000000000000000"); + + const SIXTY_FOUR: U256 = + U256::from_be_hex("FFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD03641410000000000000000"); + + #[test] + fn shl_simple() { + let mut t = U256::from(1u8); + assert_eq!(t << 1, U256::from(2u8)); + t = U256::from(3u8); + assert_eq!(t << 8, U256::from(0x300u16)); + } + + #[test] + fn shl1() { + assert_eq!(N << 1, TWO_N); + } + + #[test] + fn shl2() { + assert_eq!(N << 2, FOUR_N); + } + + #[test] + fn shl65() { + assert_eq!(N << 65, SIXTY_FIVE); + } + + #[test] + fn shl88() { + assert_eq!(N << 88, EIGHTY_EIGHT); + } + + #[test] + fn shl256() { + assert_eq!(N << 256, U256::default()); + } + + #[test] + fn shl64() { + assert_eq!(N << 64, SIXTY_FOUR); + } + + #[test] + fn shl_wide_1_1_128() { + assert_eq!( + Uint::shl_vartime_wide((U128::ONE, U128::ONE), 128), + (U128::ZERO, U128::ONE) + ); + } + + #[test] + fn shl_wide_max_0_1() { + assert_eq!( + Uint::shl_vartime_wide((U128::MAX, U128::ZERO), 1), + (U128::MAX.sbb(&U128::ONE, Limb::ZERO).0, U128::ONE) + ); + } + + #[test] + fn shl_wide_max_max_256() { + assert_eq!( + Uint::shl_vartime_wide((U128::MAX, U128::MAX), 256), + (U128::ZERO, U128::ZERO) + ); + } +} |