Update fannkuchredux benchmark

From the discussion on reddit:
http://www.reddit.com/r/rust/comments/2fenlg/benchmark_improvement_fannkuchredux/

This adds two variants: the primary, that uses an unsafe block, and a secondary
that is completely safe.

The one with the unsafe block matches clang's performance and beats gcc's.

Author: brson

src/etc/licenseck.py

@@ -44,6 +44,7 @@
     "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/test/bench/shootout-fannkuch-redux-safe.rs

@@ -0,0 +1,188 @@
+// The Computer Language Benchmarks Game
+// http://benchmarksgame.alioth.debian.org/
+//
+// contributed by the Rust Project Developers
+
+// Copyright (c) 2014 The Rust Project Developers
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+//
+// - Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in
+//   the documentation and/or other materials provided with the
+//   distribution.
+//
+// - Neither the name of "The Computer Language Benchmarks Game" nor
+//   the name of "The Computer Language Shootout Benchmarks" nor the
+//   names of its contributors may be used to endorse or promote
+//   products derived from this software without specific prior
+//   written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+// OF THE POSSIBILITY OF SUCH DAMAGE.
+
+use std::{cmp, iter, mem};
+use std::sync::Future;
+
+fn rotate(x: &mut [i32]) {
+    let mut prev = x[0];
+    for place in x.mut_iter().rev() {
+        prev = mem::replace(place, prev)
+    }
+}
+
+fn next_permutation(perm: &mut [i32], count: &mut [i32]) {
+    for i in range(1, perm.len()) {
+        rotate(perm.mut_slice_to(i + 1));
+        let count_i = &mut count[i];
+        if *count_i >= i as i32 {
+            *count_i = 0;
+        } else {
+            *count_i += 1;
+            break
+        }
+    }
+}
+
+struct P {
+    p: [i32, .. 16],
+}
+
+struct Perm {
+    cnt: [i32, .. 16],
+    fact: [u32, .. 16],
+    n: u32,
+    permcount: u32,
+    perm: P,
+}
+
+impl Perm {
+    fn new(n: u32) -> Perm {
+        let mut fact = [1, .. 16];
+        for i in range(1, n as uint + 1) {
+            fact[i] = fact[i - 1] * i as u32;
+        }
+        Perm {
+            cnt: [0, .. 16],
+            fact: fact,
+            n: n,
+            permcount: 0,
+            perm: P { p: [0, .. 16 ] }
+        }
+    }
+
+    fn get(&mut self, mut idx: i32) -> P {
+        let mut pp = [0u8, .. 16];
+        self.permcount = idx as u32;
+        for (i, place) in self.perm.p.mut_iter().enumerate() {
+            *place = i as i32 + 1;
+        }
+
+        for i in range(1, self.n as uint).rev() {
+            let d = idx / self.fact[i] as i32;
+            self.cnt[i] = d;
+            idx %= self.fact[i] as i32;
+            for (place, val) in pp.mut_iter().zip(self.perm.p.slice_to(i + 1).iter()) {
+                *place = (*val) as u8
+            }
+
+            let d = d as uint;
+            for j in range(0, i + 1) {
+                self.perm.p[j] = if j + d <= i {pp[j + d]} else {pp[j+d-i-1]} as i32;
+            }
+        }
+
+        self.perm
+    }
+
+    fn count(&self) -> u32 { self.permcount }
+    fn max(&self) -> u32 { self.fact[self.n as uint] }
+
+    fn next(&mut self) -> P {
+        next_permutation(self.perm.p, self.cnt);
+        self.permcount += 1;
+
+        self.perm
+    }
+}
+
+
+fn reverse(tperm: &mut [i32], mut k: uint) {
+    tperm.mut_slice_to(k).reverse()
+}
+
+fn work(mut perm: Perm, n: uint, max: uint) -> (i32, i32) {
+    let mut checksum = 0;
+    let mut maxflips = 0;
+
+    let mut p = perm.get(n as i32);
+
+    while perm.count() < max as u32 {
+        let mut flips = 0;
+
+        while p.p[0] != 1 {
+            let k = p.p[0] as uint;
+            reverse(p.p, k);
+            flips += 1;
+        }
+
+        checksum += if perm.count() % 2 == 0 {flips} else {-flips};
+        maxflips = cmp::max(maxflips, flips);
+
+        p = perm.next();
+    }
+
+    (checksum, maxflips)
+}
+
+fn fannkuch(n: i32) -> (i32, i32) {
+    let perm = Perm::new(n as u32);
+
+    let N = 4;
+    let mut futures = vec![];
+    let k = perm.max() / N;
+
+    for (i, j) in range(0, N).zip(iter::count(0, k)) {
+        let max = cmp::min(j+k, perm.max());
+
+        futures.push(Future::spawn(proc() {
+            work(perm, j as uint, max as uint)
+        }))
+    }
+
+    let mut checksum = 0;
+    let mut maxflips = 0;
+    for fut in futures.mut_iter() {
+        let (cs, mf) = fut.get();
+        checksum += cs;
+        maxflips = cmp::max(maxflips, mf);
+    }
+    (checksum, maxflips)
+}
+
+fn main() {
+    let n = std::os::args().as_slice()
+        .get(1)
+        .and_then(|arg| from_str(arg.as_slice()))
+        .unwrap_or(2i32);
+
+    let (checksum, maxflips) = fannkuch(n);
+    println!("{}\nPfannkuchen({}) = {}", checksum, n, maxflips);
+}