Optimize Slice::reverse

This makes the completely safe implementation of fannkuchredux perform
the same as C++. Yay, Rust.

Author: brson

src/etc/licenseck.py

@@ -44,7 +44,6 @@
     "libsync/mpsc_intrusive.rs", # BSD
     "test/bench/shootout-binarytrees.rs", # BSD
     "test/bench/shootout-fannkuch-redux.rs", # BSD
-    "test/bench/shootout-fannkuch-redux-safe.rs", # BSD
     "test/bench/shootout-k-nucleotide.rs", # BSD
     "test/bench/shootout-mandelbrot.rs", # BSD
     "test/bench/shootout-meteor.rs", # BSD

src/libcore/slice.rs

@@ -806,7 +806,12 @@ impl<'a,T> MutableSlice<'a, T> for &'a mut [T] {
         let mut i: uint = 0;
         let ln = self.len();
         while i < ln / 2 {
-            self.swap(i, ln - i - 1);
+            // Unsafe swap to avoid the bounds check in safe swap.
+            unsafe {
+                let pa: *mut T = self.unsafe_mut_ref(i);
+                let pb: *mut T = self.unsafe_mut_ref(ln - i - 1);
+                ptr::swap(pa, pb);
+            }
             i += 1;
         }
     }

src/test/bench/shootout-fannkuch-redux-safe.rs

@@ -125,13 +125,7 @@ impl Perm {
 
 
 fn reverse(tperm: &mut [i32], mut k: uint) {
-    let p = tperm.as_mut_ptr();
-
-    unsafe {
-        for off in range(0, k as int / 2) {
-            std::ptr::swap(p.offset(off), p.offset(k as int - 1 - off));
-        }
-    }
+    tperm.mut_slice_to(k).reverse()
 }
 
 fn work(mut perm: Perm, n: uint, max: uint) -> (i32, i32) {