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-rw-r--r--test/bench/go1/fannkuch_test.go84
1 files changed, 84 insertions, 0 deletions
diff --git a/test/bench/go1/fannkuch_test.go b/test/bench/go1/fannkuch_test.go
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+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// 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)
+ }
+}