From: Brendan Zabarauskas <bjzaba@yahoo.com.au>
Date: Sun, 15 Jun 2014 05:53:55 +0000 (-0700)
Subject: Add a ByteOrder trait for abstracting over endian conversions
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=87c529c43a41e0c04a468cd2b301013df629b040;p=rust.git

Add a ByteOrder trait for abstracting over endian conversions

The `Bitwise::swap_bytes` method was also moved into the `ByteOrder` trait. This was because it works on the byte level rather than the bit level.
---

diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 237efcd0096..6b08a32944c 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -13,6 +13,7 @@
 //! This module contains functions for querying the size and alignment of
 //! types, initializing and manipulating memory.
 
+use clone::Clone;
 use ptr;
 use intrinsics;
 use intrinsics::{bswap16, bswap32, bswap64};
@@ -169,151 +170,238 @@ pub unsafe fn move_val_init<T>(dst: &mut T, src: T) {
     ptr::write(dst, src)
 }
 
-/// Convert an u16 to little endian from the target's endianness.
-///
-/// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] pub fn to_le16(x: u16) -> u16 { x }
+/// A type that can have its bytes re-ordered.
+pub trait ByteOrder: Clone {
+    /// Reverses the byte order of the value.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use std::mem::ByteOrder;
+    ///
+    /// let n = 0x0123456789ABCDEFu64;
+    /// let m = 0xEFCDAB8967452301u64;
+    ///
+    /// assert_eq!(n.swap_bytes(), m);
+    /// ```
+    fn swap_bytes(&self) -> Self;
+
+    /// Convert a value from big endian to the target's endianness.
+    ///
+    /// On big endian this is a no-op. On little endian the bytes are swapped.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use std::mem::ByteOrder;
+    ///
+    /// let n = 0x0123456789ABCDEFu64;
+    ///
+    /// if cfg!(target_endian = "big") {
+    ///     assert_eq!(ByteOrder::from_big_endian(n), n)
+    /// } else {
+    ///     assert_eq!(ByteOrder::from_big_endian(n), n.swap_bytes())
+    /// }
+    /// ```
+    #[inline]
+    fn from_big_endian(x: Self) -> Self {
+        if cfg!(target_endian = "big") { x } else { x.swap_bytes() }
+    }
 
-/// Convert an u16 to little endian from the target's endianness.
-///
-/// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn to_le16(x: u16) -> u16 { unsafe { bswap16(x) } }
+    /// Convert a value from little endian to the target's endianness.
+    ///
+    /// On little endian this is a no-op. On big endian the bytes are swapped.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use std::mem::ByteOrder;
+    ///
+    /// let n = 0x0123456789ABCDEFu64;
+    ///
+    /// if cfg!(target_endian = "little") {
+    ///     assert_eq!(ByteOrder::from_little_endian(n), n)
+    /// } else {
+    ///     assert_eq!(ByteOrder::from_little_endian(n), n.swap_bytes())
+    /// }
+    /// ```
+    #[inline]
+    fn from_little_endian(x: Self) -> Self {
+        if cfg!(target_endian = "little") { x } else { x.swap_bytes() }
+    }
 
-/// Convert an u32 to little endian from the target's endianness.
-///
-/// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn to_le32(x: u32) -> u32 { x }
+    /// Convert the value to big endian from the target's endianness.
+    ///
+    /// On big endian this is a no-op. On little endian the bytes are swapped.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use std::mem::ByteOrder;
+    ///
+    /// let n = 0x0123456789ABCDEFu64;
+    ///
+    /// if cfg!(target_endian = "big") {
+    ///     assert_eq!(n.to_big_endian(), n)
+    /// } else {
+    ///     assert_eq!(n.to_big_endian(), n.swap_bytes())
+    /// }
+    /// ```
+    #[inline]
+    fn to_big_endian(&self) -> Self {
+        if cfg!(target_endian = "big") { self.clone() } else { self.swap_bytes() }
+    }
 
-/// Convert an u32 to little endian from the target's endianness.
+    /// Convert the value to little endian from the target's endianness.
+    ///
+    /// On little endian this is a no-op. On big endian the bytes are swapped.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use std::mem::ByteOrder;
+    ///
+    /// let n = 0x0123456789ABCDEFu64;
+    ///
+    /// if cfg!(target_endian = "little") {
+    ///     assert_eq!(n.to_little_endian(), n)
+    /// } else {
+    ///     assert_eq!(n.to_little_endian(), n.swap_bytes())
+    /// }
+    /// ```
+    #[inline]
+    fn to_little_endian(&self) -> Self {
+        if cfg!(target_endian = "little") { self.clone() } else { self.swap_bytes() }
+    }
+}
+
+impl ByteOrder for u8 {
+    #[inline]
+    fn swap_bytes(&self) -> u8 {
+        *self // swapping a single byte does nothing
+    }
+}
+
+impl ByteOrder for u16 {
+    #[inline]
+    fn swap_bytes(&self) -> u16 {
+        unsafe { intrinsics::bswap16(*self) }
+    }
+}
+
+impl ByteOrder for u32 {
+    #[inline]
+    fn swap_bytes(&self) -> u32 {
+        unsafe { intrinsics::bswap32(*self) }
+    }
+}
+
+impl ByteOrder for u64 {
+    #[inline]
+    fn swap_bytes(&self) -> u64 {
+        unsafe { intrinsics::bswap64(*self) }
+    }
+}
+
+#[cfg(target_word_size = "32")]
+impl ByteOrder for uint {
+    #[inline]
+    fn swap_bytes(&self) -> uint {
+        (*self as u32).swap_bytes() as uint
+    }
+}
+
+#[cfg(target_word_size = "64")]
+impl ByteOrder for uint {
+    #[inline]
+    fn swap_bytes(&self) -> uint {
+        (*self as u64).swap_bytes() as uint
+    }
+}
+
+/// Convert an u16 to little endian from the target's endianness.
 ///
 /// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn to_le32(x: u32) -> u32 { unsafe { bswap32(x) } }
+#[inline]
+#[stable]
+pub fn to_le16(x: u16) -> u16 { x.to_little_endian() }
 
-/// Convert an u64 to little endian from the target's endianness.
+/// Convert an u32 to little endian from the target's endianness.
 ///
 /// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn to_le64(x: u64) -> u64 { x }
+#[inline]
+#[stable]
+pub fn to_le32(x: u32) -> u32 { x.to_little_endian() }
 
 /// Convert an u64 to little endian from the target's endianness.
 ///
 /// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn to_le64(x: u64) -> u64 { unsafe { bswap64(x) } }
-
-
-/// Convert an u16 to big endian from the target's endianness.
-///
-/// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn to_be16(x: u16) -> u16 { unsafe { bswap16(x) } }
+#[inline]
+#[stable]
+pub fn to_le64(x: u64) -> u64 { x.to_little_endian() }
 
 /// Convert an u16 to big endian from the target's endianness.
 ///
 /// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn to_be16(x: u16) -> u16 { x }
-
-/// Convert an u32 to big endian from the target's endianness.
-///
-/// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn to_be32(x: u32) -> u32 { unsafe { bswap32(x) } }
+#[inline]
+#[stable]
+pub fn to_be16(x: u16) -> u16 { x.to_big_endian() }
 
 /// Convert an u32 to big endian from the target's endianness.
 ///
 /// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn to_be32(x: u32) -> u32 { x }
-
-/// Convert an u64 to big endian from the target's endianness.
-///
-/// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn to_be64(x: u64) -> u64 { unsafe { bswap64(x) } }
+#[inline]
+#[stable]
+pub fn to_be32(x: u32) -> u32 { x.to_big_endian() }
 
 /// Convert an u64 to big endian from the target's endianness.
 ///
 /// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn to_be64(x: u64) -> u64 { x }
-
-
-/// Convert an u16 from little endian to the target's endianness.
-///
-/// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn from_le16(x: u16) -> u16 { x }
+#[inline]
+#[stable]
+pub fn to_be64(x: u64) -> u64 { x.to_big_endian() }
 
 /// Convert an u16 from little endian to the target's endianness.
 ///
 /// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn from_le16(x: u16) -> u16 { unsafe { bswap16(x) } }
-
-/// Convert an u32 from little endian to the target's endianness.
-///
-/// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn from_le32(x: u32) -> u32 { x }
+#[inline]
+#[stable]
+pub fn from_le16(x: u16) -> u16 { ByteOrder::from_little_endian(x) }
 
 /// Convert an u32 from little endian to the target's endianness.
 ///
 /// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn from_le32(x: u32) -> u32 { unsafe { bswap32(x) } }
-
-/// Convert an u64 from little endian to the target's endianness.
-///
-/// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn from_le64(x: u64) -> u64 { x }
+#[inline]
+#[stable]
+pub fn from_le32(x: u32) -> u32 { ByteOrder::from_little_endian(x) }
 
 /// Convert an u64 from little endian to the target's endianness.
 ///
 /// On little endian, this is a no-op.  On big endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn from_le64(x: u64) -> u64 { unsafe { bswap64(x) } }
-
-
-/// Convert an u16 from big endian to the target's endianness.
-///
-/// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn from_be16(x: u16) -> u16 { unsafe { bswap16(x) } }
+#[inline]
+#[stable]
+pub fn from_le64(x: u64) -> u64 { ByteOrder::from_little_endian(x) }
 
 /// Convert an u16 from big endian to the target's endianness.
 ///
 /// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn from_be16(x: u16) -> u16 { x }
-
-/// Convert an u32 from big endian to the target's endianness.
-///
-/// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn from_be32(x: u32) -> u32 { unsafe { bswap32(x) } }
+#[inline]
+#[stable]
+pub fn from_be16(x: u16) -> u16 { ByteOrder::from_big_endian(x) }
 
 /// Convert an u32 from big endian to the target's endianness.
 ///
 /// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn from_be32(x: u32) -> u32 { x }
-
-/// Convert an u64 from big endian to the target's endianness.
-///
-/// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "little")] #[inline] #[stable]
-pub fn from_be64(x: u64) -> u64 { unsafe { bswap64(x) } }
+#[inline]
+#[stable]
+pub fn from_be32(x: u32) -> u32 { ByteOrder::from_big_endian(x) }
 
 /// Convert an u64 from big endian to the target's endianness.
 ///
 /// On big endian, this is a no-op.  On little endian, the bytes are swapped.
-#[cfg(target_endian = "big")] #[inline] #[stable]
-pub fn from_be64(x: u64) -> u64 { x }
+#[inline]
+#[stable]
+pub fn from_be64(x: u64) -> u64 { ByteOrder::from_big_endian(x) }
 
 /**
  * Swap the values at two mutable locations of the same type, without
@@ -558,6 +646,60 @@ impl Foo for int {}
             assert!(Vec::from_slice([76u8]) == transmute("L".to_string()));
         }
     }
+
+    macro_rules! test_byte_order {
+        ($T:ident) => {
+            mod $T {
+                use mem::ByteOrder;
+
+                static A: $T = 0b0101100;
+                static B: $T = 0b0100001;
+                static C: $T = 0b1111001;
+
+                static _0: $T = 0;
+                static _1: $T = !0;
+
+                #[test]
+                fn test_swap_bytes() {
+                    assert_eq!(A.swap_bytes().swap_bytes(), A);
+                    assert_eq!(B.swap_bytes().swap_bytes(), B);
+                    assert_eq!(C.swap_bytes().swap_bytes(), C);
+
+                    // Swapping these should make no difference
+                    assert_eq!(_0.swap_bytes(), _0);
+                    assert_eq!(_1.swap_bytes(), _1);
+                }
+
+                #[test]
+                fn test_little_endian() {
+                    assert_eq!(ByteOrder::from_little_endian(A.to_little_endian()), A);
+                    assert_eq!(ByteOrder::from_little_endian(B.to_little_endian()), B);
+                    assert_eq!(ByteOrder::from_little_endian(C.to_little_endian()), C);
+                    assert_eq!(ByteOrder::from_little_endian(_0), _0);
+                    assert_eq!(ByteOrder::from_little_endian(_1), _1);
+                    assert_eq!(_0.to_little_endian(), _0);
+                    assert_eq!(_1.to_little_endian(), _1);
+                }
+
+                #[test]
+                fn test_big_endian() {
+                    assert_eq!(ByteOrder::from_big_endian(A.to_big_endian()), A);
+                    assert_eq!(ByteOrder::from_big_endian(B.to_big_endian()), B);
+                    assert_eq!(ByteOrder::from_big_endian(C.to_big_endian()), C);
+                    assert_eq!(ByteOrder::from_big_endian(_0), _0);
+                    assert_eq!(ByteOrder::from_big_endian(_1), _1);
+                    assert_eq!(_0.to_big_endian(), _0);
+                    assert_eq!(_1.to_big_endian(), _1);
+                }
+            }
+        }
+    }
+
+    test_byte_order!(u8)
+    test_byte_order!(u16)
+    test_byte_order!(u32)
+    test_byte_order!(u64)
+    test_byte_order!(uint)
 }
 
 // FIXME #13642 (these benchmarks should be in another place)
diff --git a/src/libcore/num/int_macros.rs b/src/libcore/num/int_macros.rs
index 20bb12db694..8a1bd66aa1a 100644
--- a/src/libcore/num/int_macros.rs
+++ b/src/libcore/num/int_macros.rs
@@ -113,17 +113,6 @@ fn test_count_zeros() {
         assert!((0b1111001 as $T).count_zeros() == BITS as $T - 5);
     }
 
-    #[test]
-    fn test_swap_bytes() {
-        let n: $T = 0b0101100; assert_eq!(n.swap_bytes().swap_bytes(), n);
-        let n: $T = 0b0100001; assert_eq!(n.swap_bytes().swap_bytes(), n);
-        let n: $T = 0b1111001; assert_eq!(n.swap_bytes().swap_bytes(), n);
-
-        // Swapping these should make no difference
-        let n: $T = 0;   assert_eq!(n.swap_bytes(), n);
-        let n: $T = -1;  assert_eq!(n.swap_bytes(), n);
-    }
-
     #[test]
     fn test_rotate() {
         let n: $T = 0b0101100; assert_eq!(n.rotate_left(6).rotate_right(2).rotate_right(4), n);
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index eaa632be6d0..696abc05ed2 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -437,19 +437,6 @@ fn count_zeros(&self) -> Self {
     /// ```
     fn trailing_zeros(&self) -> Self;
 
-    /// Reverses the byte order of a binary number.
-    ///
-    /// # Example
-    ///
-    /// ```rust
-    /// use std::num::Bitwise;
-    ///
-    /// let n = 0x0123456789ABCDEFu64;
-    /// let m = 0xEFCDAB8967452301u64;
-    /// assert_eq!(n.swap_bytes(), m);
-    /// ```
-    fn swap_bytes(&self) -> Self;
-
     /// Shifts the bits to the left by a specified amount amount, `r`, wrapping
     /// the truncated bits to the end of the resulting value.
     ///
@@ -479,25 +466,17 @@ fn count_zeros(&self) -> Self {
     fn rotate_right(&self, r: uint) -> Self;
 }
 
-/// Swapping a single byte does nothing. This is unsafe to be consistent with
-/// the other `bswap` intrinsics.
-#[inline]
-unsafe fn bswap8(x: u8) -> u8 { x }
-
-macro_rules! bitwise_impl(
-    ($t:ty, $bits:expr, $co:ident, $lz:ident, $tz:ident, $bs:path) => {
+macro_rules! bitwise_impl {
+    ($t:ty, $bits:expr, $co:path, $lz:path, $tz:path) => {
         impl Bitwise for $t {
             #[inline]
-            fn count_ones(&self) -> $t { unsafe { intrinsics::$co(*self) } }
-
-            #[inline]
-            fn leading_zeros(&self) -> $t { unsafe { intrinsics::$lz(*self) } }
+            fn count_ones(&self) -> $t { unsafe { $co(*self) } }
 
             #[inline]
-            fn trailing_zeros(&self) -> $t { unsafe { intrinsics::$tz(*self) } }
+            fn leading_zeros(&self) -> $t { unsafe { $lz(*self) } }
 
             #[inline]
-            fn swap_bytes(&self) -> $t { unsafe { $bs(*self) } }
+            fn trailing_zeros(&self) -> $t { unsafe { $tz(*self) } }
 
             #[inline]
             fn rotate_left(&self, r: uint) -> $t {
@@ -514,22 +493,19 @@ fn rotate_right(&self, r: uint) -> $t {
             }
         }
     }
-)
+}
 
-macro_rules! bitwise_cast_impl(
-    ($t:ty, $t_cast:ty, $bits:expr,  $co:ident, $lz:ident, $tz:ident, $bs:path) => {
+macro_rules! bitwise_cast_impl {
+    ($t:ty, $t_cast:ty, $bits:expr, $co:path, $lz:path, $tz:path) => {
         impl Bitwise for $t {
             #[inline]
-            fn count_ones(&self) -> $t { unsafe { intrinsics::$co(*self as $t_cast) as $t } }
+            fn count_ones(&self) -> $t { unsafe { $co(*self as $t_cast) as $t } }
 
             #[inline]
-            fn leading_zeros(&self) -> $t { unsafe { intrinsics::$lz(*self as $t_cast) as $t } }
+            fn leading_zeros(&self) -> $t { unsafe { $lz(*self as $t_cast) as $t } }
 
             #[inline]
-            fn trailing_zeros(&self) -> $t { unsafe { intrinsics::$tz(*self as $t_cast) as $t } }
-
-            #[inline]
-            fn swap_bytes(&self) -> $t { unsafe { $bs(*self as $t_cast) as $t } }
+            fn trailing_zeros(&self) -> $t { unsafe { $tz(*self as $t_cast) as $t } }
 
             #[inline]
             fn rotate_left(&self, r: uint) -> $t {
@@ -544,27 +520,27 @@ fn rotate_right(&self, r: uint) -> $t {
             }
         }
     }
-)
+}
 
 #[cfg(target_word_size = "32")]
-bitwise_cast_impl!(uint, u32, 32, ctpop32, ctlz32, cttz32, intrinsics::bswap32)
+bitwise_cast_impl!(uint, u32, 32, intrinsics::ctpop32, intrinsics::ctlz32, intrinsics::cttz32)
 #[cfg(target_word_size = "64")]
-bitwise_cast_impl!(uint, u64, 64, ctpop64, ctlz64, cttz64, intrinsics::bswap64)
+bitwise_cast_impl!(uint, u64, 64, intrinsics::ctpop64, intrinsics::ctlz64, intrinsics::cttz64)
 
-bitwise_impl!(u8, 8, ctpop8, ctlz8, cttz8, bswap8)
-bitwise_impl!(u16, 16, ctpop16, ctlz16, cttz16, intrinsics::bswap16)
-bitwise_impl!(u32, 32, ctpop32, ctlz32, cttz32, intrinsics::bswap32)
-bitwise_impl!(u64, 64, ctpop64, ctlz64, cttz64, intrinsics::bswap64)
+bitwise_impl!(u8, 8, intrinsics::ctpop8, intrinsics::ctlz8, intrinsics::cttz8)
+bitwise_impl!(u16, 16, intrinsics::ctpop16, intrinsics::ctlz16, intrinsics::cttz16)
+bitwise_impl!(u32, 32, intrinsics::ctpop32, intrinsics::ctlz32, intrinsics::cttz32)
+bitwise_impl!(u64, 64, intrinsics::ctpop64, intrinsics::ctlz64, intrinsics::cttz64)
 
 #[cfg(target_word_size = "32")]
-bitwise_cast_impl!(int, u32, 32, ctpop32, ctlz32, cttz32, intrinsics::bswap32)
+bitwise_cast_impl!(int, u32, 32, intrinsics::ctpop32, intrinsics::ctlz32, intrinsics::cttz32)
 #[cfg(target_word_size = "64")]
-bitwise_cast_impl!(int, u64, 64, ctpop64, ctlz64, cttz64, intrinsics::bswap64)
+bitwise_cast_impl!(int, u64, 64, intrinsics::ctpop64, intrinsics::ctlz64, intrinsics::cttz64)
 
-bitwise_cast_impl!(i8, u8, 8, ctpop8, ctlz8, cttz8, bswap8)
-bitwise_cast_impl!(i16, u16, 16, ctpop16, ctlz16, cttz16, intrinsics::bswap16)
-bitwise_cast_impl!(i32, u32, 32, ctpop32, ctlz32, cttz32, intrinsics::bswap32)
-bitwise_cast_impl!(i64, u64, 64, ctpop64, ctlz64, cttz64, intrinsics::bswap64)
+bitwise_cast_impl!(i8, u8, 8, intrinsics::ctpop8, intrinsics::ctlz8, intrinsics::cttz8)
+bitwise_cast_impl!(i16, u16, 16, intrinsics::ctpop16, intrinsics::ctlz16, intrinsics::cttz16)
+bitwise_cast_impl!(i32, u32, 32, intrinsics::ctpop32, intrinsics::ctlz32, intrinsics::cttz32)
+bitwise_cast_impl!(i64, u64, 64, intrinsics::ctpop64, intrinsics::ctlz64, intrinsics::cttz64)
 
 /// Specifies the available operations common to all of Rust's core numeric primitives.
 /// These may not always make sense from a purely mathematical point of view, but
diff --git a/src/libcore/num/uint_macros.rs b/src/libcore/num/uint_macros.rs
index 8e4ba101542..8548b141053 100644
--- a/src/libcore/num/uint_macros.rs
+++ b/src/libcore/num/uint_macros.rs
@@ -64,17 +64,6 @@ fn test_count_zeros() {
         assert!((0b1111001 as $T).count_zeros() == BITS as $T - 5);
     }
 
-    #[test]
-    fn test_swap_bytes() {
-        let n: $T = 0b0101100; assert_eq!(n.swap_bytes().swap_bytes(), n);
-        let n: $T = 0b0100001; assert_eq!(n.swap_bytes().swap_bytes(), n);
-        let n: $T = 0b1111001; assert_eq!(n.swap_bytes().swap_bytes(), n);
-
-        // Swapping these should make no difference
-        let n: $T = 0;   assert_eq!(n.swap_bytes(), n);
-        let n: $T = MAX; assert_eq!(n.swap_bytes(), n);
-    }
-
     #[test]
     fn test_rotate() {
         let n: $T = 0b0101100; assert_eq!(n.rotate_left(6).rotate_right(2).rotate_right(4), n);