fannkuch-parallel.go

Documentation: golang.org/x/exp/shootout

     1  //go:build ignore
     2  // +build ignore
     3  
     4  /*
     5  Redistribution and use in source and binary forms, with or without
     6  modification, are permitted provided that the following conditions are met:
     7  
     8      * Redistributions of source code must retain the above copyright
     9      notice, this list of conditions and the following disclaimer.
    10  
    11      * Redistributions in binary form must reproduce the above copyright
    12      notice, this list of conditions and the following disclaimer in the
    13      documentation and/or other materials provided with the distribution.
    14  
    15      * Neither the name of "The Computer Language Benchmarks Game" nor the
    16      name of "The Computer Language Shootout Benchmarks" nor the names of
    17      its contributors may be used to endorse or promote products derived
    18      from this software without specific prior written permission.
    19  
    20  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    21  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    22  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    23  ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    24  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    25  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    26  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    27  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    28  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    29  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    30  POSSIBILITY OF SUCH DAMAGE.
    31  */
    32  
    33  /*
    34   * The Computer Language Benchmarks Game
    35   * http://shootout.alioth.debian.org/
    36   *
    37   * contributed by The Go Authors.
    38   * Based on fannkuch.scala by Rex Kerr
    39   */
    40  
    41  package main
    42  
    43  import (
    44  	"flag"
    45  	"fmt"
    46  	"runtime"
    47  )
    48  
    49  var n = flag.Int("n", 7, "count")
    50  var nCPU = flag.Int("ncpu", 4, "number of cpus")
    51  
    52  type Job struct {
    53  	start []int
    54  	n     int
    55  }
    56  
    57  type Found struct {
    58  	who *Kucher
    59  	k   int
    60  }
    61  
    62  type Kucher struct {
    63  	perm []int
    64  	temp []int
    65  	flip []int
    66  	in   chan Job
    67  }
    68  
    69  func NewKucher(length int) *Kucher {
    70  	return &Kucher{
    71  		perm: make([]int, length),
    72  		temp: make([]int, length),
    73  		flip: make([]int, length),
    74  		in:   make(chan Job),
    75  	}
    76  }
    77  
    78  func (k *Kucher) permute(n int) bool {
    79  	i := 0
    80  	for ; i < n-1 && k.flip[i] == 0; i++ {
    81  		t := k.perm[0]
    82  		j := 0
    83  		for ; j <= i; j++ {
    84  			k.perm[j] = k.perm[j+1]
    85  		}
    86  		k.perm[j] = t
    87  	}
    88  	k.flip[i]--
    89  	for i > 0 {
    90  		i--
    91  		k.flip[i] = i
    92  	}
    93  	return k.flip[n-1] >= 0
    94  }
    95  
    96  func (k *Kucher) count() int {
    97  	K := 0
    98  	copy(k.temp, k.perm)
    99  	for k.temp[0] != 0 {
   100  		m := k.temp[0]
   101  		for i := 0; i < m; i++ {
   102  			k.temp[i], k.temp[m] = k.temp[m], k.temp[i]
   103  			m--
   104  		}
   105  		K++
   106  	}
   107  	return K
   108  }
   109  
   110  func (k *Kucher) Run(foreman chan<- Found) {
   111  	for job := range k.in {
   112  		verbose := 30
   113  		copy(k.perm, job.start)
   114  		for i, v := range k.perm {
   115  			if v != i {
   116  				verbose = 0
   117  			}
   118  			k.flip[i] = i
   119  		}
   120  		K := 0
   121  		for {
   122  			if verbose > 0 {
   123  				for _, p := range k.perm {
   124  					fmt.Print(p + 1)
   125  				}
   126  				fmt.Println()
   127  				verbose--
   128  			}
   129  			count := k.count()
   130  			if count > K {
   131  				K = count
   132  			}
   133  			if !k.permute(job.n) {
   134  				break
   135  			}
   136  		}
   137  		foreman <- Found{k, K}
   138  	}
   139  }
   140  
   141  type Fanner struct {
   142  	jobind   int
   143  	jobsdone int
   144  	k        int
   145  	jobs     []Job
   146  	workers  []*Kucher
   147  	in       chan Found
   148  	result   chan int
   149  }
   150  
   151  func NewFanner(jobs []Job, workers []*Kucher) *Fanner {
   152  	return &Fanner{
   153  		jobs: jobs, workers: workers,
   154  		in:     make(chan Found),
   155  		result: make(chan int),
   156  	}
   157  }
   158  
   159  func (f *Fanner) Run(N int) {
   160  	for msg := range f.in {
   161  		if msg.k > f.k {
   162  			f.k = msg.k
   163  		}
   164  		if msg.k >= 0 {
   165  			f.jobsdone++
   166  		}
   167  		if f.jobind < len(f.jobs) {
   168  			msg.who.in <- f.jobs[f.jobind]
   169  			f.jobind++
   170  		} else if f.jobsdone == len(f.jobs) {
   171  			f.result <- f.k
   172  			return
   173  		}
   174  	}
   175  }
   176  
   177  func swapped(a []int, i, j int) []int {
   178  	b := make([]int, len(a))
   179  	copy(b, a)
   180  	b[i], b[j] = a[j], a[i]
   181  	return b
   182  }
   183  
   184  func main() {
   185  	flag.Parse()
   186  	runtime.GOMAXPROCS(*nCPU)
   187  	N := *n
   188  	base := make([]int, N)
   189  	for i := range base {
   190  		base[i] = i
   191  	}
   192  
   193  	njobs := 1
   194  	if N > 8 {
   195  		njobs += (N*(N-1))/2 - 28 // njobs = 1 + sum(8..N-1) = 1 + sum(1..N-1) - sum(1..7)
   196  	}
   197  	jobs := make([]Job, njobs)
   198  	jobsind := 0
   199  
   200  	firstN := N
   201  	if firstN > 8 {
   202  		firstN = 8
   203  	}
   204  	jobs[jobsind] = Job{base, firstN}
   205  	jobsind++
   206  	for i := N - 1; i >= 8; i-- {
   207  		for j := 0; j < i; j++ {
   208  			jobs[jobsind] = Job{swapped(base, i, j), i}
   209  			jobsind++
   210  		}
   211  	}
   212  
   213  	nworkers := *nCPU
   214  	if njobs < nworkers {
   215  		nworkers = njobs
   216  	}
   217  	workers := make([]*Kucher, nworkers)
   218  	foreman := NewFanner(jobs, workers)
   219  	go foreman.Run(N)
   220  	for i := range workers {
   221  		k := NewKucher(N)
   222  		workers[i] = k
   223  		go k.Run(foreman.in)
   224  		foreman.in <- Found{k, -1}
   225  	}
   226  	fmt.Printf("Pfannkuchen(%d) = %d\n", N, <-foreman.result)
   227  }
   228
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