RemMixed implementation for even splits (#791)

When the `RemMixed` trait was added in #746 I missed that we need an
impl for even splits as well. This rectifies that mistake.

Author: dvdplm

CHANGELOG.md

@@ -22,11 +22,13 @@ _The below list is very much incomplete._
 
 ### Changed
 - Make `as_limbs_mut` const ([#757])
+- Impl `RemMixed` for even splits as well ([#791])
 - Make `Integer` be fmt::Binary, LowerHex and UpperHex ([#792])
-
+-
 [#757]: https://github.com/RustCrypto/crypto-bigint/pull/757
 [#760]: https://github.com/RustCrypto/crypto-bigint/pull/760
-[#792]: https://github.com/RustCrypto/crypto-bigint/pull/792
+[#791]: https://github.com/RustCrypto/crypto-bigint/pull/791
+[#792]:https://github.com/RustCrypto/crypto-bigint/pull/792
 
 ## 0.6.0 (2025-01-22)
 ### Added

src/uint/div.rs

@@ -1114,7 +1114,7 @@ impl<const LIMBS: usize> RemLimb for Uint<LIMBS> {
 #[cfg(test)]
 mod tests {
     use crate::{
-        DivVartime, Limb, NonZero, RemMixed, U64, U128, U256, U896, U1024, Uint, Word, Zero,
+        DivVartime, Limb, NonZero, RemMixed, U64, U128, U256, U512, U896, U1024, Uint, Word, Zero,
     };
 
     #[cfg(feature = "rand")]
@@ -1391,6 +1391,29 @@ mod tests {
         );
     }
 
+    #[test]
+    fn rem_mixed_even() {
+        let x = U1024::from_be_hex(concat![
+            "3740C11DB8F260753BC6B97DD2B8746D3E2694412772AC6ABD975119EE0A6190",
+            "F27F6F0969BCA069D8D151031AF83EE2283CC2E3E4FADBBDB9EEDBF0B8F4C1FD",
+            "51912C0D329FDC37D49176DB0A1A2D17E5E6D4F9F6B217FE9412EAA2F881F702",
+            "7A831C1B06D31D3618D218D6E667DBD85BFC7B6B6B93422D52516989376AA29A",
+        ]);
+        let y = U512::from_u64(1234567890987654321);
+        let rem: U512 = x.rem_mixed(&y.to_nz().unwrap());
+
+        let y_wide = U512::concat_mixed(&y, &U512::ZERO);
+        let rem_control: U1024 = x.rem(&NonZero::new(y_wide).unwrap());
+
+        assert_eq!(rem.bits(), rem_control.bits());
+        assert_eq!(rem.as_words(), &rem_control.as_words()[0..U512::LIMBS]);
+        assert!(
+            rem_control.as_words()[U512::LIMBS..]
+                .iter()
+                .all(|w| *w == 0)
+        );
+    }
+
     #[test]
     fn rem_mixed_through_traits() {
         struct A<T, U> {

src/uint/macros.rs

@@ -102,6 +102,13 @@ macro_rules! impl_uint_concat_split_even {
             }
         }
 
+        impl $crate::traits::RemMixed<Uint<{ <$name>::LIMBS / 2 }>> for $name
+        {
+            fn rem_mixed(&self, reductor: &NonZero<Uint<{ <$name>::LIMBS / 2 }>>) -> Uint<{ <$name>::LIMBS / 2 }> {
+                self.div_rem_vartime(reductor).1
+            }
+        }
+
         impl $crate::traits::Split for $name
         {
             type Output = Uint<{ <$name>::LIMBS / 2 }>;