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24bac27632
The new math/rand/v2 package includes an m-local global random number generator that can not be reseeded by the user, which is suitable for most uses without the RNG pools we have in a number of areas of the code base. The new API still does not have an allocation-free way of performing a seeded operations, due to the long term compiler bug around interface parameter escapes, and the Source interface. This change introduces the two APIs that math/rand/v2 can not yet replace efficiently: seeded Perm() and Shuffle() operations. This implementation chooses to use the PCG random source from math/rand/v2, as with sufficient compiler optimization, this source should boil down to only two on-stack registers for random state under ideal conditions. Updates #17243 Signed-off-by: James Tucker <james@tailscale.com>
97 lines
1.9 KiB
Go
97 lines
1.9 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package rands
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import (
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"slices"
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"testing"
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randv2 "math/rand/v2"
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)
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func TestShuffleNoAllocs(t *testing.T) {
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seed := randv2.Uint64()
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data := make([]int, 100)
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for i := range data {
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data[i] = i
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}
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if n := testing.AllocsPerRun(1000, func() {
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Shuffle(seed, data)
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}); n > 0 {
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t.Errorf("Rand got %v allocs per run", n)
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}
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}
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func BenchmarkStdRandV2Shuffle(b *testing.B) {
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seed := randv2.Uint64()
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data := make([]int, 100)
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for i := range data {
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data[i] = i
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}
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b.ReportAllocs()
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for range b.N {
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// PCG is the lightest source, taking just two uint64s, the chacha8
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// source has much larger state.
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rng := randv2.New(randv2.NewPCG(seed, seed))
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rng.Shuffle(len(data), func(i, j int) { data[i], data[j] = data[j], data[i] })
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}
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}
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func BenchmarkLocalShuffle(b *testing.B) {
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seed := randv2.Uint64()
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data := make([]int, 100)
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for i := range data {
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data[i] = i
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}
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b.ReportAllocs()
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for range b.N {
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Shuffle(seed, data)
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}
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}
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func TestPerm(t *testing.T) {
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seed := uint64(12345)
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p := Perm(seed, 100)
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if len(p) != 100 {
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t.Errorf("got %v; want 100", len(p))
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}
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expect := [][]int{
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{5, 7, 1, 4, 0, 9, 2, 3, 6, 8},
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{0, 5, 9, 8, 1, 6, 2, 4, 3, 7},
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{5, 2, 3, 1, 9, 7, 6, 8, 4, 0},
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{4, 5, 7, 1, 6, 3, 8, 2, 0, 9},
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{5, 7, 0, 9, 2, 1, 8, 4, 6, 3},
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}
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for i := range 5 {
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got := Perm(seed+uint64(i), 10)
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want := expect[i]
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if !slices.Equal(got, want) {
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t.Errorf("got %v; want %v", got, want)
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}
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}
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}
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func TestShuffle(t *testing.T) {
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seed := uint64(12345)
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p := Perm(seed, 10)
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if len(p) != 10 {
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t.Errorf("got %v; want 10", len(p))
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}
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expect := [][]int{
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{9, 3, 7, 0, 5, 8, 1, 4, 2, 6},
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{9, 8, 6, 2, 3, 1, 7, 5, 0, 4},
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{1, 6, 2, 8, 4, 5, 7, 0, 3, 9},
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{4, 5, 0, 6, 7, 8, 3, 2, 1, 9},
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{8, 2, 4, 9, 0, 5, 1, 7, 3, 6},
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}
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for i := range 5 {
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Shuffle(seed+uint64(i), p)
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want := expect[i]
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if !slices.Equal(p, want) {
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t.Errorf("got %v; want %v", p, want)
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}
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}
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}
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