The Computer Language
Benchmarks Game

fannkuch-redux F# .NET Core #4 program

(* The Computer Language Benchmarks Game
   http://benchmarksgame.alioth.debian.org/

   from C# version by Isaac Gouy, transliterated from Mike Pall's Lua program 

*)
open System

let fannkuch n =
   let p = Array.init n id
   let q = Array.init n id
   let s = Array.init n id
   let mutable sign = 1
   let mutable maxflips = 0
   let mutable sum = 0
   let mutable m = n - 1
   let mutable ret = false
   let mutable res = (0,0)
   while not ret do 
         // Copy and flip.
         let mutable q0 = p.[0]                                    // Cache 0th element.
         if (q0 <> 0) then
            for i in 1 .. n - 1 do q.[i] <- p.[i]             // Work on a copy.
            let mutable flips = 1
            let mutable brk = false
            while not brk do
              let mutable qq = q.[q0] 
              if (qq = 0) then                                // ... until 0th element is 0.
                  sum <- sum + sign*flips
                  if (flips > maxflips) then maxflips <- flips    // New maximum?
                  brk <- true
               
              else
                  q.[q0] <- q0
                  if (q0 >= 3) then
                      let mutable i = 1
                      let mutable j = q0 - 1
                      let mutable brk2 = false
                      while not brk2 do 
                          let t = q.[i]
                          q.[i] <- q.[j]
                          q.[j] <- t
                          i <- i + 1
                          j <- j - 1
                          if (i >= j) then brk2 <- true
               
                  q0 <- qq
                  flips <- flips+1
            
             // Permute.
         if (sign = 1) then
             let t = p.[1]
             p.[1] <- p.[0]
             p.[0] <- t
             sign <- -1 // Rotate 0<-1.
         else 
             let t = p.[1]
             p.[1] <- p.[2]
             p.[2] <- t
             sign <- 1  // Rotate 0<-1 and 0<-1<-2.
             let mutable i = 2
             let mutable brk2 = false 
             while not ret && not brk2 do 
                 if i < n then 
                     
                     let mutable sx = s.[i]
                     if (sx <> 0) then 
                         s.[i] <- sx-1
                         brk2 <- true
                     elif (i = m) then 
                         ret <- true
                         res <- (sum, maxflips)  // Out of permutations.
                     else 
                         s.[i] <- i
                         // Rotate 0<-...<-i+1.
                         let t = p.[0]
                         for j in 0 .. i do
                             p.[j] <- p.[j+1]
                         p.[i+1] <- t
                     i <- i + 1
                 else 
                     brk2 <- true
   res

[<EntryPoint>]
let main argv = 
    let n = if (argv.Length > 0) then Int32.Parse(argv.[0]) else 7
    let (sum,maxflips) = fannkuch n
    Console.Write("{0}\nPfannkuchen({1}) = {2}\n", sum, n, maxflips)
    0
    

NOTES:
64-bit Ubuntu quad core
2.0.2 a04b4bf512
"System.GC.Server": true


Thu, 09 Nov 2017 00:00:44 GMT

MAKE:
cp fannkuchredux.fsharpcore-4.fsharpcore Program.fs
cp Include/fsharpcore/tmp.fsproj .
cp Include/fsharpcore/runtimeconfig.template.json .
mkdir obj
cp Include/fsharpcore/project.assets.json ./obj
cp Include/fsharpcore/tmp.fsproj.nuget.g.props ./obj
cp Include/fsharpcore/tmp.fsproj.nuget.g.targets ./obj
/usr/bin/dotnet build -c Release --no-restore
Microsoft (R) Build Engine version 15.4.8.50001 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  tmp -> /home/dunham/benchmarksgame_quadcore/fannkuchredux/tmp/bin/Release/netcoreapp2.0/tmp.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:08.79

9.37s to complete and log all make actions

COMMAND LINE:
/usr/bin/dotnet ./bin/Release/netcoreapp2.0/tmp.dll 12

PROGRAM OUTPUT:
3968050
Pfannkuchen(12) = 65