source code
// The Computer Language Benchmarks Game
// https://benchmarksgame-team.pages.debian.net/benchmarksgame/
//
// contributed by Flim Nik
// small optimisations by Anthony Lloyd
using System;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading;
public unsafe static class FannkuchRedux
{
static int taskCount;
static int[] fact, chkSums, maxFlips;
[MethodImpl(MethodImplOptions.AggressiveInlining)]
static void FirstPermutation(short* p, short* pp, int* count, int n, int idx)
{
for (int i = 0; i < n; ++i) p[i] = (byte)i;
for (int i = n - 1; i > 0; --i)
{
int d = idx / fact[i];
count[i] = d;
if (d > 0)
{
idx %= fact[i];
for (int j = i; j >= 0; --j) pp[j] = p[j];
for (int j = 0; j <= i; ++j) p[j] = pp[(j + d) % (i + 1)];
}
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
static void NextPermutation(short* p, int* count)
{
var first = p[1];
p[1] = p[0];
p[0] = first;
int i = 1;
while (++count[i] > i)
{
count[i++] = 0;
var next = p[1];
p[0] = next;
for (int j = 1; j < i;) p[j] = p[++j];
p[i] = first;
first = next;
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
static void Copy(short* p, short* pp, int n)
{
var startL = (long*)p;
var stateL = (long*)pp;
var lengthL = n / 4;
int i = 0;
for (; i < lengthL; i++)
{
stateL[i] = startL[i];
}
for (i = lengthL * 4; i < n; i++)
{
pp[i] = p[i];
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
static int CountFlips(short* p, short* pp, int n)
{
int flips = 1;
int first = *p;
short temp;
if (p[first] != 0)
{
Copy(p, pp, n);
do
{
++flips;
if (first > 2)
{
short* lo = pp + 1, hi = pp + first - 1;
do
{
temp = *lo;
*lo = *hi;
*hi = temp;
} while (++lo < --hi);
}
temp = pp[first];
pp[first] = (short)first;
first = temp;
} while (pp[first] != 0);
}
return flips;
}
static void Run(int n, int taskSize)
{
int* count = stackalloc int[n];
int taskId, chksum = 0, maxflips = 0;
short* p = stackalloc short[n];
short* pp = stackalloc short[n];
while ((taskId = Interlocked.Decrement(ref taskCount)) >= 0)
{
FirstPermutation(p, pp, count, n, taskId * taskSize);
if (*p != 0)
{
var flips = CountFlips(p, pp, n);
chksum += flips;
if (flips > maxflips) maxflips = flips;
}
for (int i = 1; i < taskSize; i++)
{
NextPermutation(p, count);
if (*p != 0)
{
var flips = CountFlips(p, pp, n);
chksum += (1 - (i & 1) * 2) * flips;
if (flips > maxflips) maxflips = flips;
}
}
}
chkSums[-taskId - 1] = chksum;
maxFlips[-taskId - 1] = maxflips;
}
public static void Main(string[] args)
{
int n = args.Length > 0 ? int.Parse(args[0]) : 7;
fact = new int[n + 1];
fact[0] = 1;
for (int i = 1; i < fact.Length; i++)
{
fact[i] = fact[i - 1] * i;
}
var PC = Environment.ProcessorCount;
taskCount = n > 11 ? fact[n] / (9 * 8 * 7 * 6 * 5 * 4 * 3 * 2) : PC;
int taskSize = fact[n] / taskCount;
chkSums = new int[PC];
maxFlips = new int[PC];
var threads = new Thread[PC];
for (int i = 1; i < PC; i++)
{
(threads[i] = new Thread(() => Run(n, taskSize))).Start();
}
Run(n, taskSize);
for (int i = 1; i < threads.Length; i++)
{
threads[i].Join();
}
Console.WriteLine(chkSums.Sum() + "\nPfannkuchen(" + n + ") = " + maxFlips.Max());
}
}
notes, command-line, and program output
NOTES:
64-bit Ubuntu quad core
.NET SDK 8.0.200
Host Version: 8.0.2
Commit: 1381d5ebd2
<ServerGarbageCollection>true
<PublishAot>true
Thu, 07 Mar 2024 00:08:51 GMT
MAKE:
cp fannkuchredux.csharpaot-9.csharpaot Program.cs
cp Include/csharpaot/tmp.csproj .
mkdir obj
cp Include/csharpaot/project.assets.json ./obj
/usr/bin/dotnet publish -c Release -r linux-x64
MSBuild version 17.9.4+90725d08d for .NET
Determining projects to restore...
Restored /home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/tmp.csproj (in 959 ms).
/home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/Program.cs(15,18): warning CS8618: Non-nullable field 'fact' must contain a non-null value when exiting constructor. Consider declaring the field as nullable. [/home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/tmp.csproj]
/home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/Program.cs(15,24): warning CS8618: Non-nullable field 'chkSums' must contain a non-null value when exiting constructor. Consider declaring the field as nullable. [/home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/tmp.csproj]
/home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/Program.cs(15,33): warning CS8618: Non-nullable field 'maxFlips' must contain a non-null value when exiting constructor. Consider declaring the field as nullable. [/home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/tmp.csproj]
tmp -> /home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/bin/Release/net8.0/linux-x64/tmp.dll
Generating native code
tmp -> /home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/bin/Release/net8.0/linux-x64/publish/
18.84s to complete and log all make actions
COMMAND LINE:
./bin/Release/net8.0/linux-x64/publish/tmp 12
PROGRAM OUTPUT:
3968050
Pfannkuchen(12) = 65