Add functions for reversing the bit pattern in an integer

src/libcore/intrinsics.rs

@@ -584,6 +584,10 @@ extern "rust-intrinsic" {
     /// Reverses the bytes in an integer type `T`.
     pub fn bswap<T>(x: T) -> T;
 
+    /// Reverses the bits in an integer type `T`.
+    #[cfg(not(stage0))]
+    pub fn bitreverse<T>(x: T) -> T;
+
     /// Performs checked integer addition.
     pub fn add_with_overflow<T>(x: T, y: T) -> (T, bool);
 

src/libcore/num/mod.rs

@@ -224,6 +224,24 @@ macro_rules! int_impl {
             (self as $UnsignedT).trailing_zeros()
         }
 
+        /// Reverses the bit pattern of the integer.
+        ///
+        /// # Examples
+        ///
+        /// Basic usage:
+        ///
+        /// ```
+        /// let n = 0b10101000u8;
+        ///
+        /// assert_eq!(n.reverse_bits(), 0b00010101u8);
+        /// ```
+        #[cfg(not(stage0))]
+        #[unstable(feature = "reverse_bits", issue = "0", reason = "recently added")]
+        #[inline]
+        pub fn reverse_bits(self) -> Self {
+            (self as $UnsignedT).reverse_bits() as Self
+        }
+
         /// Shifts the bits to the left by a specified amount, `n`,
         /// wrapping the truncated bits to the end of the resulting integer.
         ///
@@ -1290,6 +1308,24 @@ macro_rules! uint_impl {
             }
         }
 
+        /// Reverses the bit pattern of the integer.
+        ///
+        /// # Examples
+        ///
+        /// Basic usage:
+        ///
+        /// ```
+        /// let n = 0b10101000u8;
+        ///
+        /// assert_eq!(n.reverse_bits(), 0b00010101u8);
+        /// ```
+        #[cfg(not(stage0))]
+        #[unstable(feature = "reverse_bits", issue = "0", reason = "recently added")]
+        #[inline]
+        pub fn reverse_bits(self) -> Self {
+            unsafe { intrinsics::bitreverse(self) }
+        }
+
         /// Shifts the bits to the left by a specified amount, `n`,
         /// wrapping the truncated bits to the end of the resulting integer.
         ///

src/librustc_trans/context.rs

@@ -1001,6 +1001,11 @@ fn declare_intrinsic(ccx: &CrateContext, key: &str) -> Option<ValueRef> {
     ifn!("llvm.bswap.i32", fn(t_i32) -> t_i32);
     ifn!("llvm.bswap.i64", fn(t_i64) -> t_i64);
 
+    ifn!("llvm.bitreverse.i8", fn(t_i8) -> t_i8);
+    ifn!("llvm.bitreverse.i16", fn(t_i16) -> t_i16);
+    ifn!("llvm.bitreverse.i32", fn(t_i32) -> t_i32);
+    ifn!("llvm.bitreverse.i64", fn(t_i64) -> t_i64);
+
     ifn!("llvm.sadd.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct!{t_i8, i1});
     ifn!("llvm.sadd.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct!{t_i16, i1});
     ifn!("llvm.sadd.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct!{t_i32, i1});

src/librustc_trans/intrinsic.rs

@@ -607,7 +607,7 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
             C_nil(ccx)
         },
 
-        (_, "ctlz") | (_, "cttz") | (_, "ctpop") | (_, "bswap") |
+        (_, "ctlz") | (_, "cttz") | (_, "ctpop") | (_, "bswap") | (_, "bitreverse") |
         (_, "add_with_overflow") | (_, "sub_with_overflow") | (_, "mul_with_overflow") |
         (_, "overflowing_add") | (_, "overflowing_sub") | (_, "overflowing_mul") |
         (_, "unchecked_div") | (_, "unchecked_rem") => {
@@ -629,6 +629,9 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
                                         &llargs, call_debug_location)
                             }
                         }
+                        "bitreverse" => Call(bcx, ccx.get_intrinsic(&format!("llvm.bitreverse.i{}",
+                                                                    width)),
+                                             &llargs, call_debug_location),
                         "add_with_overflow" | "sub_with_overflow" | "mul_with_overflow" => {
                             let intrinsic = format!("llvm.{}{}.with.overflow.i{}",
                                                     if signed { 's' } else { 'u' },

src/librustc_typeck/check/intrinsic.rs

@@ -265,7 +265,8 @@ pub fn check_intrinsic_type(ccx: &CrateCtxt, it: &hir::ForeignItem) {
             "volatile_store" =>
                 (1, vec!( tcx.mk_mut_ptr(param(ccx, 0)), param(ccx, 0) ), tcx.mk_nil()),
 
-            "ctpop" | "ctlz" | "cttz" | "bswap" => (1, vec!(param(ccx, 0)), param(ccx, 0)),
+            "ctpop" | "ctlz" | "cttz" | "bswap" | "bitreverse" =>
+                (1, vec!(param(ccx, 0)), param(ccx, 0)),
 
             "add_with_overflow" | "sub_with_overflow"  | "mul_with_overflow" =>
                 (1, vec!(param(ccx, 0), param(ccx, 0)),

src/test/run-pass/intrinsics-integer.rs

@@ -16,6 +16,7 @@ mod rusti {
         pub fn ctlz<T>(x: T) -> T;
         pub fn cttz<T>(x: T) -> T;
         pub fn bswap<T>(x: T) -> T;
+        pub fn bitreverse<T>(x: T) -> T;
     }
 }
 
@@ -101,5 +102,14 @@ pub fn main() {
         assert_eq!(bswap(0x0ABBCC0Di32), 0x0DCCBB0A);
         assert_eq!(bswap(0x0122334455667708u64), 0x0877665544332201);
         assert_eq!(bswap(0x0122334455667708i64), 0x0877665544332201);
+
+        assert_eq!(bitreverse(0x0Au8), 0x50);
+        assert_eq!(bitreverse(0x0Ai8), 0x50);
+        assert_eq!(bitreverse(0x0A0Cu16), 0x3050);
+        assert_eq!(bitreverse(0x0A0Ci16), 0x3050);
+        assert_eq!(bitreverse(0x0ABBCC0Eu32), 0x7033DD50);
+        assert_eq!(bitreverse(0x0ABBCC0Ei32), 0x7033DD50);
+        assert_eq!(bitreverse(0x0122334455667708u64), 0x10EE66AA22CC4480);
+        assert_eq!(bitreverse(0x0122334455667708i64), 0x10EE66AA22CC4480);
     }
 }