1 files changed, 176 insertions, 0 deletions
diff --git a/vendor/crypto-bigint/src/limb/cmp.rs b/vendor/crypto-bigint/src/limb/cmp.rs
new file mode 100644
index 000000000..76cc4b07c
--- /dev/null
+++ b/vendor/crypto-bigint/src/limb/cmp.rs
@@ -0,0 +1,176 @@
+//! Limb comparisons
+
+use super::{Limb, SignedWord, WideSignedWord, Word, HI_BIT};
+use core::cmp::Ordering;
+use subtle::{Choice, ConstantTimeEq, ConstantTimeGreater, ConstantTimeLess};
+
+impl Limb {
+    /// Is this limb an odd number?
+    #[inline]
+    pub fn is_odd(&self) -> Choice {
+        Choice::from(self.0 as u8 & 1)
+    }
+
+    /// Perform a comparison of the inner value in variable-time.
+    ///
+    /// Note that the [`PartialOrd`] and [`Ord`] impls wrap constant-time
+    /// comparisons using the `subtle` crate.
+    pub fn cmp_vartime(&self, other: &Self) -> Ordering {
+        self.0.cmp(&other.0)
+    }
+
+    /// Performs an equality check in variable-time.
+    pub const fn eq_vartime(&self, other: &Self) -> bool {
+        self.0 == other.0
+    }
+
+    /// Returns all 1's if `a`!=0 or 0 if `a`==0.
+    ///
+    /// Const-friendly: we can't yet use `subtle` in `const fn` contexts.
+    #[inline]
+    pub(crate) const fn is_nonzero(self) -> Word {
+        let inner = self.0 as SignedWord;
+        ((inner | inner.saturating_neg()) >> HI_BIT) as Word
+    }
+
+    #[inline]
+    pub(crate) const fn ct_cmp(lhs: Self, rhs: Self) -> SignedWord {
+        let a = lhs.0 as WideSignedWord;
+        let b = rhs.0 as WideSignedWord;
+        let gt = ((b - a) >> Limb::BIT_SIZE) & 1;
+        let lt = ((a - b) >> Limb::BIT_SIZE) & 1 & !gt;
+        (gt as SignedWord) - (lt as SignedWord)
+    }
+}
+
+impl ConstantTimeEq for Limb {
+    #[inline]
+    fn ct_eq(&self, other: &Self) -> Choice {
+        self.0.ct_eq(&other.0)
+    }
+}
+
+impl ConstantTimeGreater for Limb {
+    #[inline]
+    fn ct_gt(&self, other: &Self) -> Choice {
+        self.0.ct_gt(&other.0)
+    }
+}
+
+impl ConstantTimeLess for Limb {
+    #[inline]
+    fn ct_lt(&self, other: &Self) -> Choice {
+        self.0.ct_lt(&other.0)
+    }
+}
+
+impl Eq for Limb {}
+
+impl Ord for Limb {
+    fn cmp(&self, other: &Self) -> Ordering {
+        let mut n = 0i8;
+        n -= self.ct_lt(other).unwrap_u8() as i8;
+        n += self.ct_gt(other).unwrap_u8() as i8;
+
+        match n {
+            -1 => Ordering::Less,
+            1 => Ordering::Greater,
+            _ => {
+                debug_assert_eq!(n, 0);
+                debug_assert!(bool::from(self.ct_eq(other)));
+                Ordering::Equal
+            }
+        }
+    }
+}
+
+impl PartialOrd for Limb {
+    #[inline]
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl PartialEq for Limb {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.ct_eq(other).into()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Limb, Zero};
+    use core::cmp::Ordering;
+    use subtle::{ConstantTimeEq, ConstantTimeGreater, ConstantTimeLess};
+
+    #[test]
+    fn is_zero() {
+        assert!(bool::from(Limb::ZERO.is_zero()));
+        assert!(!bool::from(Limb::ONE.is_zero()));
+        assert!(!bool::from(Limb::MAX.is_zero()));
+    }
+
+    #[test]
+    fn is_odd() {
+        assert!(!bool::from(Limb::ZERO.is_odd()));
+        assert!(bool::from(Limb::ONE.is_odd()));
+        assert!(bool::from(Limb::MAX.is_odd()));
+    }
+
+    #[test]
+    fn ct_eq() {
+        let a = Limb::ZERO;
+        let b = Limb::MAX;
+
+        assert!(bool::from(a.ct_eq(&a)));
+        assert!(!bool::from(a.ct_eq(&b)));
+        assert!(!bool::from(b.ct_eq(&a)));
+        assert!(bool::from(b.ct_eq(&b)));
+    }
+
+    #[test]
+    fn ct_gt() {
+        let a = Limb::ZERO;
+        let b = Limb::ONE;
+        let c = Limb::MAX;
+
+        assert!(bool::from(b.ct_gt(&a)));
+        assert!(bool::from(c.ct_gt(&a)));
+        assert!(bool::from(c.ct_gt(&b)));
+
+        assert!(!bool::from(a.ct_gt(&a)));
+        assert!(!bool::from(b.ct_gt(&b)));
+        assert!(!bool::from(c.ct_gt(&c)));
+
+        assert!(!bool::from(a.ct_gt(&b)));
+        assert!(!bool::from(a.ct_gt(&c)));
+        assert!(!bool::from(b.ct_gt(&c)));
+    }
+
+    #[test]
+    fn ct_lt() {
+        let a = Limb::ZERO;
+        let b = Limb::ONE;
+        let c = Limb::MAX;
+
+        assert!(bool::from(a.ct_lt(&b)));
+        assert!(bool::from(a.ct_lt(&c)));
+        assert!(bool::from(b.ct_lt(&c)));
+
+        assert!(!bool::from(a.ct_lt(&a)));
+        assert!(!bool::from(b.ct_lt(&b)));
+        assert!(!bool::from(c.ct_lt(&c)));
+
+        assert!(!bool::from(b.ct_lt(&a)));
+        assert!(!bool::from(c.ct_lt(&a)));
+        assert!(!bool::from(c.ct_lt(&b)));
+    }
+
+    #[test]
+    fn cmp() {
+        assert_eq!(Limb::ZERO.cmp(&Limb::ONE), Ordering::Less);
+        assert_eq!(Limb::ONE.cmp(&Limb::ONE), Ordering::Equal);
+        assert_eq!(Limb::MAX.cmp(&Limb::ONE), Ordering::Greater);
+    }
+}