/
rand.go
57 lines (48 loc) · 1.33 KB
/
rand.go
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package utils
import (
"math/rand"
"sync"
"time"
)
// Rand return an random number between [min, max)
func Rand(min, max int) int {
return rand.Intn(max-min) + min
}
const (
LettersAlphaNumber = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
LettersNumber = "0123456789"
LettersAlpha = "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
)
var randSrcPool *sync.Pool
// nolint:gochecknoinits
func init() {
randSrcPool = &sync.Pool{
New: func() any {
return rand.NewSource(time.Now().UnixNano())
},
}
}
// RandString return a random string of length n
func RandString(n int, letterBytes string) string {
src := randSrcPool.Get().(rand.Source)
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--
}
randSrcPool.Put(src)
return string(b)
}