modulo benchmarking for https://github.com/elastic/go-freelru/pull/60

modulo.go

package modulo

func fastModulo(x, n uint32) uint32 {
	return uint32((uint64(x) * uint64(n)) >> 32)
}

func regularModulo(x, n uint32) uint32 {
	return x % n
}

modulo_test.go

package modulo

import (
	"fmt"
	"testing"
)

func BenchmarkModulo(b *testing.B) {
	testCases := []struct {
		name string
		fn   func(uint32, uint32) uint32
	}{
		{"FastModulo", fastModulo},
		{"RegularModulo", regularModulo},
	}

	values := []struct {
		x, n uint32
	}{
		{x: 3, n: 4095},
		{x: 4095, n: 3},
		{x: 65535, n: 19},
		{x: 19, n: 65535},
		{x: 65535 - 1, n: 19},
		{x: 19, n: 65535 - 1},
		{x: 4_294_967_295 - 1, n: 65535},
		{x: 4_294_967_295 - 1, n: 65535 - 1},
	}

	for _, tc := range testCases {
		for _, value := range values {
			b.Run(tc.name+fmt.Sprintf("_%d over %d", value.x, value.n), func(b *testing.B) {
				for i := 0; i < b.N; i++ {
					_ = tc.fn(value.x, value.n)
				}
			})
		}
	}
}

output.log

$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: xch.gl/modulo
cpu: 12th Gen Intel(R) Core(TM) i7-12700H
BenchmarkModulo/FastModulo_3_over_4095-20         	1000000000	         1.141 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_4095_over_3-20         	1000000000	         1.138 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_65535_over_19-20       	1000000000	         1.137 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_19_over_65535-20       	1000000000	         1.134 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_65534_over_19-20       	1000000000	         1.136 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_19_over_65534-20       	1000000000	         1.150 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_4294967294_over_65535-20         	1000000000	         1.161 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/FastModulo_4294967294_over_65534-20         	1000000000	         1.166 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_3_over_4095-20                	908406850	         1.307 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_4095_over_3-20                	914586667	         1.298 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_65535_over_19-20              	912191052	         1.307 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_19_over_65535-20              	917458092	         1.298 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_65534_over_19-20              	907173954	         1.310 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_19_over_65534-20              	915687758	         1.294 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_4294967294_over_65535-20      	927088612	         1.310 ns/op	       0 B/op	       0 allocs/op
BenchmarkModulo/RegularModulo_4294967294_over_65534-20      	914863524	         1.289 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	xch.gl/modulo	20.744s