crypto_bigint/uint/
neg.rs

1use core::ops::Neg;
2
3use crate::{CtChoice, Limb, Uint, WideWord, Word, Wrapping};
4
5impl<const LIMBS: usize> Neg for Wrapping<Uint<LIMBS>> {
6    type Output = Self;
7
8    fn neg(self) -> Self::Output {
9        Self(self.0.wrapping_neg())
10    }
11}
12
13impl<const LIMBS: usize> Uint<LIMBS> {
14    /// Negates based on `choice` by wrapping the integer.
15    pub(crate) const fn conditional_wrapping_neg(&self, choice: CtChoice) -> Uint<LIMBS> {
16        Uint::ct_select(self, &self.wrapping_neg(), choice)
17    }
18
19    /// Perform wrapping negation.
20    pub const fn wrapping_neg(&self) -> Self {
21        let mut ret = [Limb::ZERO; LIMBS];
22        let mut carry = 1;
23        let mut i = 0;
24        while i < LIMBS {
25            let r = (!self.limbs[i].0 as WideWord) + carry;
26            ret[i] = Limb(r as Word);
27            carry = r >> Limb::BITS;
28            i += 1;
29        }
30        Uint::new(ret)
31    }
32}
33
34#[cfg(test)]
35mod tests {
36    use crate::U256;
37
38    #[test]
39    fn wrapping_neg() {
40        assert_eq!(U256::ZERO.wrapping_neg(), U256::ZERO);
41        assert_eq!(U256::MAX.wrapping_neg(), U256::ONE);
42        assert_eq!(
43            U256::from_u64(13).wrapping_neg(),
44            U256::from_u64(13).not().saturating_add(&U256::ONE)
45        );
46        assert_eq!(
47            U256::from_u64(42).wrapping_neg(),
48            U256::from_u64(42).saturating_sub(&U256::ONE).not()
49        );
50    }
51}
crypto_bigint/uint/neg.rs

crypto_bigint/uint/
neg.rs
