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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
// Adapted from fannkuch-redux C# .NET Core #2 program
// http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fannkuchredux&lang=csharpcore&id=2
// Best-scoring single-threaded C# .NET Core version as of 2017-09-01
/* The Computer Language Benchmarks Game
http://benchmarksgame.alioth.debian.org/
contributed by Isaac Gouy, transliterated from Mike Pall's Lua program
*/
using System;
using Microsoft.Xunit.Performance;
using Xunit;
[assembly: OptimizeForBenchmarks]
namespace BenchmarksGame
{
public class FannkuchRedux_2
{
public static int[] fannkuch(int n)
{
int[] p = new int[n], q = new int[n], s = new int[n];
int sign = 1, maxflips = 0, sum = 0, m = n - 1;
for (int i = 0; i < n; i++) { p[i] = i; q[i] = i; s[i] = i; }
do
{
// Copy and flip.
var q0 = p[0]; // Cache 0th element.
if (q0 != 0)
{
for (int i = 1; i < n; i++) q[i] = p[i]; // Work on a copy.
var flips = 1;
do
{
var qq = q[q0];
if (qq == 0)
{ // ... until 0th element is 0.
sum += sign * flips;
if (flips > maxflips) maxflips = flips; // New maximum?
break;
}
q[q0] = q0;
if (q0 >= 3)
{
int i = 1, j = q0 - 1, t;
do { t = q[i]; q[i] = q[j]; q[j] = t; i++; j--; } while (i < j);
}
q0 = qq; flips++;
} while (true);
}
// Permute.
if (sign == 1)
{
var t = p[1]; p[1] = p[0]; p[0] = t; sign = -1; // Rotate 0<-1.
}
else
{
var t = p[1]; p[1] = p[2]; p[2] = t; sign = 1; // Rotate 0<-1 and 0<-1<-2.
for (int i = 2; i < n; i++)
{
var sx = s[i];
if (sx != 0) { s[i] = sx - 1; break; }
if (i == m) return new int[] { sum, maxflips }; // Out of permutations.
s[i] = i;
// Rotate 0<-...<-i+1.
t = p[0]; for (int j = 0; j <= i; j++) { p[j] = p[j + 1]; }
p[i + 1] = t;
}
}
} while (true);
}
static int Main(string[] args)
{
int n = (args.Length > 0) ? Int32.Parse(args[0]) : 7;
var pf = fannkuch(n);
Console.Write("{0}\nPfannkuchen({1}) = {2}\n", pf[0], n, pf[1]);
int expected = 228;
// Return 100 on success, anything else on failure.
return pf[0] - expected + 100;
}
[Benchmark(InnerIterationCount = 7)]
[InlineData(10, 73196)]
public static void RunBench(int n, int expectedSum)
{
Benchmark.Iterate(() =>
{
var pf = fannkuch(n);
Assert.Equal(expectedSum, pf[0]);
});
}
}
}
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