optimize Range[Inclusive].count()

Author: llogiq

src/libcore/iter/range.rs

@@ -268,6 +268,31 @@ impl<A: Step> Iterator for ops::Range<A> {
     }
 }
 
+macro_rules! impl_range_count {
+    ($t:ty) => {
+        #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+        impl Iterator for ops::Range<$t> {
+            #[inline]
+            fn count(self) -> usize {
+                self.end.wrapping_sub(self.start) as usize
+            }
+        }
+    };
+}
+
+impl_range_count!(u8);
+impl_range_count!(u16);
+impl_range_count!(u32);
+impl_range_count!(u64);
+impl_range_count!(usize);
+
+impl_range_count!(i8);
+impl_range_count!(i16);
+impl_range_count!(i32);
+impl_range_count!(i64);
+impl_range_count!(isize);
+
+
 // These macros generate `ExactSizeIterator` impls for various range types.
 // Range<{u,i}64> and RangeInclusive<{u,i}{32,64,size}> are excluded
 // because they cannot guarantee having a length <= usize::MAX, which is
@@ -421,6 +446,30 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
     }
 }
 
+macro_rules! impl_inclusive_range_count {
+    ($t:ty) => {
+        #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+        impl Iterator for ops::RangeInclusive<$t> {
+            #[inline]
+            fn count(self) -> usize {
+                (self.end.wrapping_sub(self.start) as usize).wrapping_add(1)
+            }
+        }
+    };
+}
+
+impl_inclusive_range_count!(u8);
+impl_inclusive_range_count!(u16);
+impl_inclusive_range_count!(u32);
+impl_inclusive_range_count!(u64);
+impl_inclusive_range_count!(usize);
+
+impl_inclusive_range_count!(i8);
+impl_inclusive_range_count!(i16);
+impl_inclusive_range_count!(i32);
+impl_inclusive_range_count!(i64);
+impl_inclusive_range_count!(isize);
+
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
     #[inline]

src/libcore/tests/iter.rs

@@ -1391,6 +1391,13 @@ fn test_range_inclusive_nth() {
     assert_eq!(r, 1..=0);  // We may not want to document/promise this detail
 }
 
+#[test]
+fn test_range_inclusive_count() {
+    assert_eq!((1..=1).count(), 1);
+    assert_eq!((0..=10).count(), 11);
+    assert_eq!((5..=7).count(), 3);
+}
+
 #[test]
 fn test_range_step() {
     #![allow(deprecated)]