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use core::ops::Neg;
use crate::{CtChoice, Limb, Uint, WideWord, Word, Wrapping};
impl<const LIMBS: usize> Neg for Wrapping<Uint<LIMBS>> {
type Output = Self;
fn neg(self) -> Self::Output {
Self(self.0.wrapping_neg())
}
}
impl<const LIMBS: usize> Uint<LIMBS> {
/// Negates based on `choice` by wrapping the integer.
pub(crate) const fn conditional_wrapping_neg(&self, choice: CtChoice) -> Uint<LIMBS> {
Uint::ct_select(self, &self.wrapping_neg(), choice)
}
/// Perform wrapping negation.
pub const fn wrapping_neg(&self) -> Self {
let mut ret = [Limb::ZERO; LIMBS];
let mut carry = 1;
let mut i = 0;
while i < LIMBS {
let r = (!self.limbs[i].0 as WideWord) + carry;
ret[i] = Limb(r as Word);
carry = r >> Limb::BITS;
i += 1;
}
Uint::new(ret)
}
}
#[cfg(test)]
mod tests {
use crate::U256;
#[test]
fn wrapping_neg() {
assert_eq!(U256::ZERO.wrapping_neg(), U256::ZERO);
assert_eq!(U256::MAX.wrapping_neg(), U256::ONE);
assert_eq!(
U256::from_u64(13).wrapping_neg(),
U256::from_u64(13).not().saturating_add(&U256::ONE)
);
assert_eq!(
U256::from_u64(42).wrapping_neg(),
U256::from_u64(42).saturating_sub(&U256::ONE).not()
);
}
}
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