--- /dev/null
+/*
+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.
+*/
+
+/*
+ * The Computer Language Benchmarks Game
+ * http://shootout.alioth.debian.org/
+ *
+ * contributed by The Go Authors.
+ * Based on fannkuch.scala by Rex Kerr
+ */
+
+package main
+
+import (
+ "flag"
+ "fmt"
+ "runtime"
+)
+
+var n = flag.Int("n", 7, "count")
+var nCPU = flag.Int("ncpu", 2, "number of cpus")
+
+type Job struct {
+ start []int
+ n int
+}
+
+type Found struct {
+ who *Kucher
+ k int
+}
+
+type Kucher struct {
+ perm []int
+ temp []int
+ flip []int
+ in chan Job
+}
+
+func NewKucher(length int) *Kucher {
+ return &Kucher{
+ perm: make([]int, length),
+ temp: make([]int, length),
+ flip: make([]int, length),
+ in: make(chan Job),
+ }
+}
+
+func (k *Kucher) permute(n int) bool {
+ i := 0
+ for ; i < n-1 && k.flip[i] == 0; i++ {
+ t := k.perm[0]
+ j := 0
+ for ; j <= i; j++ {
+ k.perm[j] = k.perm[j+1]
+ }
+ k.perm[j] = t
+ }
+ k.flip[i]--
+ for i > 0 {
+ i--
+ k.flip[i] = i
+ }
+ return k.flip[n-1] >= 0
+}
+
+func (k *Kucher) count() int {
+ K := 0
+ copy(k.temp, k.perm)
+ for k.temp[0] != 0 {
+ m := k.temp[0]
+ for i := 0; i < m; i++ {
+ k.temp[i], k.temp[m] = k.temp[m], k.temp[i]
+ m--
+ }
+ K++
+ }
+ return K
+}
+
+func (k *Kucher) Run(foreman chan<- Found) {
+ for job := range k.in {
+ verbose := 30
+ copy(k.perm, job.start)
+ for i, v := range k.perm {
+ if v != i {
+ verbose = 0
+ }
+ k.flip[i] = i
+ }
+ K := 0
+ for {
+ if verbose > 0 {
+ for _, p := range k.perm {
+ fmt.Print(p + 1)
+ }
+ fmt.Println()
+ verbose--
+ }
+ count := k.count()
+ if count > K {
+ K = count
+ }
+ if !k.permute(job.n) {
+ break
+ }
+ }
+ foreman <- Found{k, K}
+ }
+}
+
+type Fanner struct {
+ jobind int
+ jobsdone int
+ k int
+ jobs []Job
+ workers []*Kucher
+ in chan Found
+ result chan int
+}
+
+func NewFanner(jobs []Job, workers []*Kucher) *Fanner {
+ return &Fanner{
+ jobs: jobs, workers: workers,
+ in: make(chan Found),
+ result: make(chan int),
+ }
+}
+
+func (f *Fanner) Run(N int) {
+ for msg := range f.in {
+ if msg.k > f.k {
+ f.k = msg.k
+ }
+ if msg.k >= 0 {
+ f.jobsdone++
+ }
+ if f.jobind < len(f.jobs) {
+ msg.who.in <- f.jobs[f.jobind]
+ f.jobind++
+ } else if f.jobsdone == len(f.jobs) {
+ f.result <- f.k
+ return
+ }
+ }
+}
+
+func swapped(a []int, i, j int) []int {
+ b := make([]int, len(a))
+ copy(b, a)
+ b[i], b[j] = a[j], a[i]
+ return b
+}
+
+func main() {
+ flag.Parse()
+ runtime.GOMAXPROCS(*nCPU)
+ N := *n
+ base := make([]int, N)
+ for i := range base {
+ base[i] = i
+ }
+
+ njobs := 1
+ if N > 8 {
+ njobs += (N*(N-1))/2 - 28 // njobs = 1 + sum(8..N-1) = 1 + sum(1..N-1) - sum(1..7)
+ }
+ jobs := make([]Job, njobs)
+ jobsind := 0
+
+ firstN := N
+ if firstN > 8 {
+ firstN = 8
+ }
+ jobs[jobsind] = Job{base, firstN}
+ jobsind++
+ for i := N - 1; i >= 8; i-- {
+ for j := 0; j < i; j++ {
+ jobs[jobsind] = Job{swapped(base, i, j), i}
+ jobsind++
+ }
+ }
+
+ nworkers := *nCPU
+ if njobs < nworkers {
+ nworkers = njobs
+ }
+ workers := make([]*Kucher, nworkers)
+ foreman := NewFanner(jobs, workers)
+ go foreman.Run(N)
+ for i := range workers {
+ k := NewKucher(N)
+ workers[i] = k
+ go k.Run(foreman.in)
+ foreman.in <- Found{k, -1}
+ }
+ fmt.Printf("Pfannkuchen(%d) = %d\n", N, <-foreman.result)
+}