benchmarks for possible implementations for github.com/golang/go/issues/6721

test-rand.go

package main

import (
	"math"
	"testing"
)

const bits32 = 24
const step32 float32 = 1 / (1 << bits32)
const mask32 uint32 = (1 << bits32) - 1

func Float32(i uint32) float32 {
	return float32(i&mask32) * step32
}

const bits64 = 53
const step64 float64 = 1 / (1 << bits64)
const mask64 uint64 = (1 << bits64) - 1

func Float64(i uint64) float64 {
	return float64(i&mask64) * step64
}

func Float64b(i uint64) float64 {
	return (float64(i >> 10)) * (1.0 / 9007199254740992.0)
}

const range_1_2Exp64 = 0x3ff0000000000000
const mantissaMask64 = 0x000fffffffffffff

func Float64c(i uint64) float64 {
	return math.Float64frombits(range_1_2Exp64|(mantissaMask64&i)) - 1.0
}

func BenchmarkF64a(b *testing.B) {
	for i := 0; i < b.N; i++ {
		Float64(uint64(i))
	}
}

func BenchmarkF64b(b *testing.B) {
	for i := 0; i < b.N; i++ {
		Float64b(uint64(i))
	}
}

func BenchmarkF64c(b *testing.B) {
	for i := 0; i < b.N; i++ {
		Float64c(uint64(i))
	}
}