Add reverse_bits to integer types

Author: Amanieu

src/libcore/num/mod.rs

@@ -321,6 +321,33 @@ $EndFeature, "
             (self as $UnsignedT).swap_bytes() as Self
         }
 
+        /// Reverses the bit pattern of the integer.
+        ///
+        /// # Examples
+        ///
+        /// Please note that this example is shared between integer types.
+        /// Which explains why `i16` is used here.
+        ///
+        /// Basic usage:
+        ///
+        /// ```
+        /// #![feature(reverse_bits)]
+        ///
+        /// let n: i16 = 0b0000000_01010101;
+        /// assert_eq!(n, 85);
+        ///
+        /// let m = n.reverse_bits();
+        ///
+        /// assert_eq!(m as u16, 0b10101010_00000000);
+        /// assert_eq!(m, -22016);
+        /// ```
+        #[unstable(feature = "reverse_bits", issue = "48763")]
+        #[cfg(not(stage0))]
+        #[inline]
+        pub fn reverse_bits(self) -> Self {
+            (self as $UnsignedT).reverse_bits() as Self
+        }
+
         doc_comment! {
             concat!("Converts an integer from big endian to the target's endianness.
 
@@ -1773,6 +1800,33 @@ assert_eq!(n.trailing_zeros(), 3);", $EndFeature, "
             unsafe { intrinsics::bswap(self as $ActualT) as Self }
         }
 
+        /// Reverses the bit pattern of the integer.
+        ///
+        /// # Examples
+        ///
+        /// Basic usage:
+        ///
+        /// Please note that this example is shared between integer types.
+        /// Which explains why `u16` is used here.
+        ///
+        /// ```
+        /// #![feature(reverse_bits)]
+        ///
+        /// let n: u16 = 0b0000000_01010101;
+        /// assert_eq!(n, 85);
+        ///
+        /// let m = n.reverse_bits();
+        ///
+        /// assert_eq!(m, 0b10101010_00000000);
+        /// assert_eq!(m, 43520);
+        /// ```
+        #[unstable(feature = "reverse_bits", issue = "48763")]
+        #[cfg(not(stage0))]
+        #[inline]
+        pub fn reverse_bits(self) -> Self {
+            unsafe { intrinsics::bitreverse(self as $ActualT) as Self }
+        }
+
         doc_comment! {
             concat!("Converts an integer from big endian to the target's endianness.
 

src/libcore/tests/lib.rs

@@ -46,6 +46,7 @@
 #![feature(try_trait)]
 #![feature(exact_chunks)]
 #![feature(atomic_nand)]
+#![feature(reverse_bits)]
 
 extern crate core;
 extern crate test;

src/libcore/tests/num/uint_macros.rs

@@ -97,6 +97,17 @@ mod tests {
         assert_eq!(_1.swap_bytes(), _1);
     }
 
+    #[test]
+    fn test_reverse_bits() {
+        assert_eq!(A.reverse_bits().reverse_bits(), A);
+        assert_eq!(B.reverse_bits().reverse_bits(), B);
+        assert_eq!(C.reverse_bits().reverse_bits(), C);
+
+        // Swapping these should make no difference
+        assert_eq!(_0.reverse_bits(), _0);
+        assert_eq!(_1.reverse_bits(), _1);
+    }
+
     #[test]
     fn test_le() {
         assert_eq!($T::from_le(A.to_le()), A);