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()

        );

    }

}