1 files changed, 215 insertions, 0 deletions
diff --git a/vendor/crypto-bigint/src/uint/sub.rs b/vendor/crypto-bigint/src/uint/sub.rs
new file mode 100644
index 0000000..571dd6a
--- /dev/null
+++ b/vendor/crypto-bigint/src/uint/sub.rs
@@ -0,0 +1,215 @@
+//! [`Uint`] addition operations.
+
+use super::Uint;
+use crate::{Checked, CheckedSub, CtChoice, Limb, Wrapping, Zero};
+use core::ops::{Sub, SubAssign};
+use subtle::CtOption;
+
+impl<const LIMBS: usize> Uint<LIMBS> {
+    /// Computes `a - (b + borrow)`, returning the result along with the new borrow.
+    #[inline(always)]
+    pub const fn sbb(&self, rhs: &Self, mut borrow: Limb) -> (Self, Limb) {
+        let mut limbs = [Limb::ZERO; LIMBS];
+        let mut i = 0;
+
+        while i < LIMBS {
+            let (w, b) = self.limbs[i].sbb(rhs.limbs[i], borrow);
+            limbs[i] = w;
+            borrow = b;
+            i += 1;
+        }
+
+        (Self { limbs }, borrow)
+    }
+
+    /// Perform saturating subtraction, returning `ZERO` on underflow.
+    pub const fn saturating_sub(&self, rhs: &Self) -> Self {
+        let (res, underflow) = self.sbb(rhs, Limb::ZERO);
+        Self::ct_select(&res, &Self::ZERO, CtChoice::from_mask(underflow.0))
+    }
+
+    /// Perform wrapping subtraction, discarding underflow and wrapping around
+    /// the boundary of the type.
+    pub const fn wrapping_sub(&self, rhs: &Self) -> Self {
+        self.sbb(rhs, Limb::ZERO).0
+    }
+
+    /// Perform wrapping subtraction, returning the truthy value as the second element of the tuple
+    /// if an underflow has occurred.
+    pub(crate) const fn conditional_wrapping_sub(
+        &self,
+        rhs: &Self,
+        choice: CtChoice,
+    ) -> (Self, CtChoice) {
+        let actual_rhs = Uint::ct_select(&Uint::ZERO, rhs, choice);
+        let (res, borrow) = self.sbb(&actual_rhs, Limb::ZERO);
+        (res, CtChoice::from_mask(borrow.0))
+    }
+}
+
+impl<const LIMBS: usize> CheckedSub<&Uint<LIMBS>> for Uint<LIMBS> {
+    type Output = Self;
+
+    fn checked_sub(&self, rhs: &Self) -> CtOption<Self> {
+        let (result, underflow) = self.sbb(rhs, Limb::ZERO);
+        CtOption::new(result, underflow.is_zero())
+    }
+}
+
+impl<const LIMBS: usize> Sub for Wrapping<Uint<LIMBS>> {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Wrapping<Uint<LIMBS>> {
+        Wrapping(self.0.wrapping_sub(&rhs.0))
+    }
+}
+
+impl<const LIMBS: usize> Sub<&Wrapping<Uint<LIMBS>>> for Wrapping<Uint<LIMBS>> {
+    type Output = Wrapping<Uint<LIMBS>>;
+
+    fn sub(self, rhs: &Wrapping<Uint<LIMBS>>) -> Wrapping<Uint<LIMBS>> {
+        Wrapping(self.0.wrapping_sub(&rhs.0))
+    }
+}
+
+impl<const LIMBS: usize> Sub<Wrapping<Uint<LIMBS>>> for &Wrapping<Uint<LIMBS>> {
+    type Output = Wrapping<Uint<LIMBS>>;
+
+    fn sub(self, rhs: Wrapping<Uint<LIMBS>>) -> Wrapping<Uint<LIMBS>> {
+        Wrapping(self.0.wrapping_sub(&rhs.0))
+    }
+}
+
+impl<const LIMBS: usize> Sub<&Wrapping<Uint<LIMBS>>> for &Wrapping<Uint<LIMBS>> {
+    type Output = Wrapping<Uint<LIMBS>>;
+
+    fn sub(self, rhs: &Wrapping<Uint<LIMBS>>) -> Wrapping<Uint<LIMBS>> {
+        Wrapping(self.0.wrapping_sub(&rhs.0))
+    }
+}
+
+impl<const LIMBS: usize> SubAssign for Wrapping<Uint<LIMBS>> {
+    fn sub_assign(&mut self, other: Self) {
+        *self = *self - other;
+    }
+}
+
+impl<const LIMBS: usize> SubAssign<&Wrapping<Uint<LIMBS>>> for Wrapping<Uint<LIMBS>> {
+    fn sub_assign(&mut self, other: &Self) {
+        *self = *self - other;
+    }
+}
+
+impl<const LIMBS: usize> Sub for Checked<Uint<LIMBS>> {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Checked<Uint<LIMBS>> {
+        Checked(
+            self.0
+                .and_then(|lhs| rhs.0.and_then(|rhs| lhs.checked_sub(&rhs))),
+        )
+    }
+}
+
+impl<const LIMBS: usize> Sub<&Checked<Uint<LIMBS>>> for Checked<Uint<LIMBS>> {
+    type Output = Checked<Uint<LIMBS>>;
+
+    fn sub(self, rhs: &Checked<Uint<LIMBS>>) -> Checked<Uint<LIMBS>> {
+        Checked(
+            self.0
+                .and_then(|lhs| rhs.0.and_then(|rhs| lhs.checked_sub(&rhs))),
+        )
+    }
+}
+
+impl<const LIMBS: usize> Sub<Checked<Uint<LIMBS>>> for &Checked<Uint<LIMBS>> {
+    type Output = Checked<Uint<LIMBS>>;
+
+    fn sub(self, rhs: Checked<Uint<LIMBS>>) -> Checked<Uint<LIMBS>> {
+        Checked(
+            self.0
+                .and_then(|lhs| rhs.0.and_then(|rhs| lhs.checked_sub(&rhs))),
+        )
+    }
+}
+
+impl<const LIMBS: usize> Sub<&Checked<Uint<LIMBS>>> for &Checked<Uint<LIMBS>> {
+    type Output = Checked<Uint<LIMBS>>;
+
+    fn sub(self, rhs: &Checked<Uint<LIMBS>>) -> Checked<Uint<LIMBS>> {
+        Checked(
+            self.0
+                .and_then(|lhs| rhs.0.and_then(|rhs| lhs.checked_sub(&rhs))),
+        )
+    }
+}
+
+impl<const LIMBS: usize> SubAssign for Checked<Uint<LIMBS>> {
+    fn sub_assign(&mut self, other: Self) {
+        *self = *self - other;
+    }
+}
+
+impl<const LIMBS: usize> SubAssign<&Checked<Uint<LIMBS>>> for Checked<Uint<LIMBS>> {
+    fn sub_assign(&mut self, other: &Self) {
+        *self = *self - other;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{CheckedSub, Limb, U128};
+
+    #[test]
+    fn sbb_no_borrow() {
+        let (res, borrow) = U128::ONE.sbb(&U128::ONE, Limb::ZERO);
+        assert_eq!(res, U128::ZERO);
+        assert_eq!(borrow, Limb::ZERO);
+    }
+
+    #[test]
+    fn sbb_with_borrow() {
+        let (res, borrow) = U128::ZERO.sbb(&U128::ONE, Limb::ZERO);
+
+        assert_eq!(res, U128::MAX);
+        assert_eq!(borrow, Limb::MAX);
+    }
+
+    #[test]
+    fn saturating_sub_no_borrow() {
+        assert_eq!(
+            U128::from(5u64).saturating_sub(&U128::ONE),
+            U128::from(4u64)
+        );
+    }
+
+    #[test]
+    fn saturating_sub_with_borrow() {
+        assert_eq!(
+            U128::from(4u64).saturating_sub(&U128::from(5u64)),
+            U128::ZERO
+        );
+    }
+
+    #[test]
+    fn wrapping_sub_no_borrow() {
+        assert_eq!(U128::ONE.wrapping_sub(&U128::ONE), U128::ZERO);
+    }
+
+    #[test]
+    fn wrapping_sub_with_borrow() {
+        assert_eq!(U128::ZERO.wrapping_sub(&U128::ONE), U128::MAX);
+    }
+
+    #[test]
+    fn checked_sub_ok() {
+        let result = U128::ONE.checked_sub(&U128::ONE);
+        assert_eq!(result.unwrap(), U128::ZERO);
+    }
+
+    #[test]
+    fn checked_sub_overflow() {
+        let result = U128::ZERO.checked_sub(&U128::ONE);
+        assert!(!bool::from(result.is_some()));
+    }
+}