Merging upstream version 1.70.0+dfsg2.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/vendor/crypto-bigint/src/uint/neg_mod.rs b/vendor/crypto-bigint/src/uint/neg_mod.rs
new file mode 100644
index 000000000..0a1dc033a
--- /dev/null
+++ b/vendor/crypto-bigint/src/uint/neg_mod.rs
@@ -0,0 +1,68 @@
+//! [`UInt`] negation modulus operations.
+
+use crate::{Limb, NegMod, UInt};
+
+impl<const LIMBS: usize> UInt<LIMBS> {
+    /// Computes `-a mod p` in constant time.
+    /// Assumes `self` is in `[0, p)`.
+    pub const fn neg_mod(&self, p: &Self) -> Self {
+        let z = self.ct_is_nonzero();
+        let mut ret = p.sbb(self, Limb::ZERO).0;
+        let mut i = 0;
+        while i < LIMBS {
+            // Set ret to 0 if the original value was 0, in which
+            // case ret would be p.
+            ret.limbs[i].0 &= z;
+            i += 1;
+        }
+        ret
+    }
+
+    /// Computes `-a mod p` in constant time for the special modulus
+    /// `p = MAX+1-c` where `c` is small enough to fit in a single [`Limb`].
+    pub const fn neg_mod_special(&self, c: Limb) -> Self {
+        Self::ZERO.sub_mod_special(self, c)
+    }
+}
+
+impl<const LIMBS: usize> NegMod for UInt<LIMBS> {
+    type Output = Self;
+
+    fn neg_mod(&self, p: &Self) -> Self {
+        debug_assert!(self < p);
+        self.neg_mod(p)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::U256;
+
+    #[test]
+    fn neg_mod_random() {
+        let x =
+            U256::from_be_hex("8d16e171674b4e6d8529edba4593802bf30b8cb161dd30aa8e550d41380007c2");
+        let p =
+            U256::from_be_hex("928334a4e4be0843ec225a4c9c61df34bdc7a81513e4b6f76f2bfa3148e2e1b5");
+
+        let actual = x.neg_mod(&p);
+        let expected =
+            U256::from_be_hex("056c53337d72b9d666f86c9256ce5f08cabc1b63b207864ce0d6ecf010e2d9f3");
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn neg_mod_zero() {
+        let x =
+            U256::from_be_hex("0000000000000000000000000000000000000000000000000000000000000000");
+        let p =
+            U256::from_be_hex("928334a4e4be0843ec225a4c9c61df34bdc7a81513e4b6f76f2bfa3148e2e1b5");
+
+        let actual = x.neg_mod(&p);
+        let expected =
+            U256::from_be_hex("0000000000000000000000000000000000000000000000000000000000000000");
+
+        assert_eq!(expected, actual);
+    }
+}