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 // Copyright 2021 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. package test import ( "math/bits" "testing" ) func BenchmarkSwitch8Predictable(b *testing.B) { benchmarkSwitch8(b, true) } func BenchmarkSwitch8Unpredictable(b *testing.B) { benchmarkSwitch8(b, false) } func benchmarkSwitch8(b *testing.B, predictable bool) { n := 0 rng := newRNG() for i := 0; i < b.N; i++ { rng = rng.next(predictable) switch rng.value() & 7 { case 0: n += 1 case 1: n += 2 case 2: n += 3 case 3: n += 4 case 4: n += 5 case 5: n += 6 case 6: n += 7 case 7: n += 8 } } sink = n } func BenchmarkSwitch32Predictable(b *testing.B) { benchmarkSwitch32(b, true) } func BenchmarkSwitch32Unpredictable(b *testing.B) { benchmarkSwitch32(b, false) } func benchmarkSwitch32(b *testing.B, predictable bool) { n := 0 rng := newRNG() for i := 0; i < b.N; i++ { rng = rng.next(predictable) switch rng.value() & 31 { case 0, 1, 2: n += 1 case 4, 5, 6: n += 2 case 8, 9, 10: n += 3 case 12, 13, 14: n += 4 case 16, 17, 18: n += 5 case 20, 21, 22: n += 6 case 24, 25, 26: n += 7 case 28, 29, 30: n += 8 default: n += 9 } } sink = n } func BenchmarkSwitchStringPredictable(b *testing.B) { benchmarkSwitchString(b, true) } func BenchmarkSwitchStringUnpredictable(b *testing.B) { benchmarkSwitchString(b, false) } func benchmarkSwitchString(b *testing.B, predictable bool) { a := []string{ "foo", "foo1", "foo22", "foo333", "foo4444", "foo55555", "foo666666", "foo7777777", } n := 0 rng := newRNG() for i := 0; i < b.N; i++ { rng = rng.next(predictable) switch a[rng.value()&7] { case "foo": n += 1 case "foo1": n += 2 case "foo22": n += 3 case "foo333": n += 4 case "foo4444": n += 5 case "foo55555": n += 6 case "foo666666": n += 7 case "foo7777777": n += 8 } } sink = n } // A simple random number generator used to make switches conditionally predictable. type rng uint64 func newRNG() rng { return 1 } func (r rng) next(predictable bool) rng { if predictable { return r + 1 } return rng(bits.RotateLeft64(uint64(r), 13) * 0x3c374d) } func (r rng) value() uint64 { return uint64(r) }