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# Source file test/bench/go1/fannkuch_test.go

## Documentation: test/bench/go1

```  // Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style

// This benchmark, taken from the shootout, tests array indexing
// and array bounds elimination performance.

package go1

import "testing"

func fannkuch(n int) int {
if n < 1 {
return 0
}

n1 := n - 1
perm := make([]int, n)
perm1 := make([]int, n)
count := make([]int, n)

for i := 0; i < n; i++ {
perm1[i] = i // initial (trivial) permutation
}

r := n
didpr := 0
flipsMax := 0
for {
if didpr < 30 {
didpr++
}
for ; r != 1; r-- {
count[r-1] = r
}

if perm1[0] != 0 && perm1[n1] != n1 {
flips := 0
for i := 1; i < n; i++ { // perm = perm1
perm[i] = perm1[i]
}
k := perm1[0] // cache perm[0] in k
for {         // k!=0 ==> k>0
for i, j := 1, k-1; i < j; i, j = i+1, j-1 {
perm[i], perm[j] = perm[j], perm[i]
}
flips++
// Now exchange k (caching perm[0]) and perm[k]... with care!
j := perm[k]
perm[k] = k
k = j
if k == 0 {
break
}
}
if flipsMax < flips {
flipsMax = flips
}
}

for ; r < n; r++ {
// rotate down perm[0..r] by one
perm0 := perm1[0]
for i := 0; i < r; i++ {
perm1[i] = perm1[i+1]
}
perm1[r] = perm0
count[r]--
if count[r] > 0 {
break
}
}
if r == n {
return flipsMax
}
}
return 0
}

func BenchmarkFannkuch11(b *testing.B) {
for i := 0; i < b.N; i++ {
fannkuch(11)
}
}

```

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