testing.B.ReportMetric

benchstat

% benchstat bubble.txt selection.txt
name    old time/op      new time/op      delta
Sort-4      29.4ns ± 1%      29.1ns ± 0%  -1.00%  (p=0.016 n=5+4)

name    old compares/op  new compares/op  delta
Sort-4        15.0 ± 0%        15.0 ± 0%    ~     (all equal)

name    old alloc/op     new alloc/op     delta
Sort-4       0.00B            0.00B         ~     (all equal)

name    old allocs/op    new allocs/op    delta
Sort-4        0.00             0.00         ~     (all equal)

bubble.txt

goos: linux
goarch: amd64
BenchmarkSort-4         40962218                29.3 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         41243956                29.6 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         40784164                29.6 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         40886186                29.4 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         41580344                29.2 ns/op              15.0 compares/op               0 B/op          0 allocs/op
PASS
ok      _/usr/local/google/home/yoshifumi/tmp/bench     10.884s

foo.go

package foo

func bubbleSort(s []int, compares *int) []int {
        for i := 0; i < len(s)-1; i++ {
                for j := i + 1; j < len(s); j++ {
                        *compares++
                        if s[i] > s[j] {
                                s[i], s[j] = s[j], s[i]
                        }
                }
        }
        return s
}

func selectionSort(s []int, compares *int) []int {
        for i := 0; i < len(s)-1; i++ {
                pos := i
                for j := i + 1; j < len(s); j++ {
                        *compares++
                        if s[pos] > s[j] {
                                pos = j
                        }
                }
                s[i], s[pos] = s[pos], s[i]
        }
        return s
}

func sort(s []int, compares *int) []int {
        //      return bubbleSort(s, compares)
        return selectionSort(s, compares)
}

foo_test.go

package foo

import "testing"

func TestSort(t *testing.T) {
        in := []int{3, 2, 1, 4, 6, 5}
        want := []int{1, 2, 3, 4, 5, 6}

        var n int
        out := sort(in, &n)
        for i, w := range want {
                if out[i] != w {
                        t.Errorf("want: %v, out: %v", w, out[i])
                }
        }
}

func BenchmarkSort(b *testing.B) {
        var compares int
        for i := 0; i < b.N; i++ {
                sort([]int{3, 5, 1, 2, 6, 4}, &compares)
        }
        b.ReportMetric(float64(compares)/float64(b.N), "compares/op")
}

selection.txt

goos: linux
goarch: amd64
BenchmarkSort-4         40892257                29.2 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         41086053                29.1 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         40863766                28.5 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         41608278                29.1 ns/op              15.0 compares/op               0 B/op          0 allocs/op
BenchmarkSort-4         39724590                29.1 ns/op              15.0 compares/op               0 B/op          0 allocs/op
PASS
ok      _/usr/local/google/home/yoshifumi/tmp/bench     9.908s