package main
import (
"math/rand"
"strings"
"testing"
"time"
"unsafe"
)
// Implementations
func init() {
rand.Seed(time.Now().UnixNano())
}
var letterRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
func RandStringRunes(n int) string {
b := make([]rune, n)
for i := range b {
b[i] = letterRunes[rand.Intn(len(letterRunes))]
}
return string(b)
}
const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
const (
letterIdxBits = 6 // 6 bits to represent a letter index
letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
)
func RandStringBytes(n int) string {
b := make([]byte, n)
for i := range b {
b[i] = letterBytes[rand.Intn(len(letterBytes))]
}
return string(b)
}
func RandStringBytesRmndr(n int) string {
b := make([]byte, n)
for i := range b {
b[i] = letterBytes[rand.Int63()%int64(len(letterBytes))]
}
return string(b)
}
func RandStringBytesMask(n int) string {
b := make([]byte, n)
for i := 0; i < n; {
if idx := int(rand.Int63() & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i++
}
}
return string(b)
}
func RandStringBytesMaskImpr(n int) string {
b := make([]byte, n)
// A rand.Int63() generates 63 random bits, enough for letterIdxMax letters!
for i, cache, remain := n-1, rand.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = rand.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}
var src = rand.NewSource(time.Now().UnixNano())
func RandStringBytesMaskImprSrc(n int) string {
b := make([]byte, n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}
func RandStringBytesMaskImprSrcSB(n int) string {
sb := strings.Builder{}
sb.Grow(n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
sb.WriteByte(letterBytes[idx])
i--
}
cache >>= letterIdxBits
remain--
}
return sb.String()
}
func RandStringBytesMaskImprSrcUnsafe(n int) string {
b := make([]byte, n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return *(*string)(unsafe.Pointer(&b))
}
// Benchmark functions
const n = 16
func BenchmarkRunes(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringRunes(n)
}
}
func BenchmarkBytes(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytes(n)
}
}
func BenchmarkBytesRmndr(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytesRmndr(n)
}
}
func BenchmarkBytesMask(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytesMask(n)
}
}
func BenchmarkBytesMaskImpr(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytesMaskImpr(n)
}
}
func BenchmarkBytesMaskImprSrc(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytesMaskImprSrc(n)
}
}
func BenchmarkBytesMaskImprSrcSB(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytesMaskImprSrcSB(n)
}
}
func BenchmarkBytesMaskImprSrcUnsafe(b *testing.B) {
for i := 0; i < b.N; i++ {
RandStringBytesMaskImprSrcUnsafe(n)
}
}