reduce allocations in shr

rust-num · Feb 8, 2018 · e45b2b7 · e45b2b7
1 parent 4714f82
commit e45b2b7
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/src/algorithms.rs b/src/algorithms.rs
@@ -591,9 +591,12 @@ pub fn biguint_shr(n: Cow<BigUint>, bits: usize) -> BigUint {
     if n_unit >= n.data.len() {
         return Zero::zero();
     }
-    let mut data = match n_unit {
-        0 => n.into_owned().data,
-        _ => n.data[n_unit..].to_vec(),
+    let mut data = match n {
+        Cow::Borrowed(n) => n.data[n_unit..].to_vec(),
+        Cow::Owned(mut n) => {
+            n.data.drain(..n_unit);
+            n.data
+        }
     };
 
     let n_bits = bits % big_digit::BITS;

diff --git a/src/biguint.rs b/src/biguint.rs
@@ -398,7 +398,8 @@ impl<'a> Shr<usize> for &'a BigUint {
 impl ShrAssign<usize> for BigUint {
     #[inline]
     fn shr_assign(&mut self, rhs: usize) {
-        *self = biguint_shr(Cow::Borrowed(&*self), rhs);
+        let n = mem::replace(self, BigUint::zero());
+        *self = n >> rhs;
     }
 }