bjoernager/rust
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Optimize Slice::reverse

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This makes the completely safe implementation of fannkuchredux perform
the same as C++. Yay, Rust.
This commit is contained in:
Brian Anderson 2014-09-04 19:54:41 -07:00
parent fc3b6383ba
commit 7e12e67936
4 changed files with 7 additions and 197 deletions
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1
src/etc/licenseck.py
View file

@ -44,7 +44,6 @@ exceptions = [
"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

7
src/libcore/slice.rs
View file

@ -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;
}
}

188
src/test/bench/shootout-fannkuch-redux-safe.rs
View file

@ -1,188 +0,0 @@
// 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);
}

8
src/test/bench/shootout-fannkuch-redux.rs
View file

@ -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) {