/
rand.go
59 lines (51 loc) · 1.56 KB
/
rand.go
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// Copyright 2016 ~ 2018 AlexStocks(https://github.com/AlexStocks).
// All rights reserved. Use of this source code is
// governed by Apache License 2.0.
// Package gxrand encapsulates some golang.math.rand functions
package gxrand
import (
"math/rand"
"time"
)
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
letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
digitStrings = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
)
var (
src = rand.NewSource(time.Now().UnixNano())
)
func RandString(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 RandDigitString(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(digitStrings) {
b[i] = digitStrings[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}