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

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// xfail-test reading from os::args()[1] - bogus!

use std::from_str::FromStr;
use std::os;
use std::vec::MutableVector;
use std::vec;

fn max(a: i32, b: i32) -> i32 {
    if a > b {
        a
    } else {
        b
    }
}

#[inline(never)]
fn fannkuch_redux(n: i32) -> i32 {
    let mut perm = vec::from_elem(n as uint, 0i32);
    let mut perm1 = vec::from_fn(n as uint, |i| i as i32);
    let mut count = vec::from_elem(n as uint, 0i32);
    let mut max_flips_count = 0i32;
    let mut perm_count = 0i32;
    let mut checksum = 0i32;

    let mut r = n;
    loop {
        unsafe {
            while r != 1 {
                count.unsafe_set((r-1) as uint, r);
                r -= 1;
            }

            for (perm_i, perm1_i) in perm.mut_iter().zip(perm1.iter()) {
                *perm_i = *perm1_i;
            }

            let mut flips_count: i32 = 0;
            let mut k: i32;
            loop {
                k = *perm.unsafe_ref(0);
                if k == 0 {
                    break;
                }

                let k2 = (k+1) >> 1;
                for i in range(0i32, k2) {
                    let (perm_i, perm_k_i) = {
                        (*perm.unsafe_ref(i as uint),
                            *perm.unsafe_ref((k-i) as uint))
                    };
                    perm.unsafe_set(i as uint, perm_k_i);
                    perm.unsafe_set((k-i) as uint, perm_i);
                }
                flips_count += 1;
            }

            max_flips_count = max(max_flips_count, flips_count);
            checksum += if perm_count % 2 == 0 {
                flips_count
            } else {
                -flips_count
            };

            // Use incremental change to generate another permutation.
            loop {
                if r == n {
                    println!("{}", checksum);
                    return max_flips_count;
                }

                let perm0 = perm1[0];
                let mut i: i32 = 0;
                while i < r {
                    let j = i + 1;
                    let perm1_j = { *perm1.unsafe_ref(j as uint) };
                    perm1.unsafe_set(i as uint, perm1_j);
                    i = j;
                }
                perm1.unsafe_set(r as uint, perm0);

                let count_r = { *count.unsafe_ref(r as uint) };
                count.unsafe_set(r as uint, count_r - 1);
                if *count.unsafe_ref(r as uint) > 0 {
                    break;
                }
                r += 1;
            }

            perm_count += 1;
        }
    }
}

fn main() {
    let n: i32 = FromStr::from_str(os::args()[1]).unwrap();
    println!("Pfannkuchen({}) = {}", n as int, fannkuch_redux(n) as int);
}