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85 lines
1.5 KiB
85 lines
1.5 KiB
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This benchmark, taken from the shootout, tests array indexing
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// and array bounds elimination performance.
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package go1
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import "testing"
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func fannkuch(n int) int {
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if n < 1 {
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return 0
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}
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n1 := n - 1
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perm := make([]int, n)
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perm1 := make([]int, n)
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count := make([]int, n)
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for i := 0; i < n; i++ {
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perm1[i] = i // initial (trivial) permutation
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}
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r := n
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didpr := 0
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flipsMax := 0
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for {
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if didpr < 30 {
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didpr++
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}
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for ; r != 1; r-- {
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count[r-1] = r
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}
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if perm1[0] != 0 && perm1[n1] != n1 {
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flips := 0
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for i := 1; i < n; i++ { // perm = perm1
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perm[i] = perm1[i]
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}
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k := perm1[0] // cache perm[0] in k
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for { // k!=0 ==> k>0
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for i, j := 1, k-1; i < j; i, j = i+1, j-1 {
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perm[i], perm[j] = perm[j], perm[i]
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}
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flips++
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// Now exchange k (caching perm[0]) and perm[k]... with care!
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j := perm[k]
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perm[k] = k
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k = j
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if k == 0 {
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break
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}
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}
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if flipsMax < flips {
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flipsMax = flips
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}
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}
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for ; r < n; r++ {
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// rotate down perm[0..r] by one
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perm0 := perm1[0]
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for i := 0; i < r; i++ {
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perm1[i] = perm1[i+1]
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}
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perm1[r] = perm0
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count[r]--
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if count[r] > 0 {
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break
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}
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}
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if r == n {
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return flipsMax
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}
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}
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return 0
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}
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func BenchmarkFannkuch11(b *testing.B) {
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for i := 0; i < b.N; i++ {
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fannkuch(11)
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}
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}
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