simplemq/lib/random/lib.go

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1.4 KiB
Go
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2021-11-15 23:06:05 +00:00
package random
import (
"math/rand"
"time"
"unsafe"
)
const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
const upperBytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
const letterNumsBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
const letterNumsUpperBytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
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 src = rand.NewSource(time.Now().UnixNano())
func strFromSrc(n int, srcChars string) 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(srcChars) {
b[i] = srcChars[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return *(*string)(unsafe.Pointer(&b))
}
func Str(n int) string {
return strFromSrc(n, letterBytes)
}
func StrUpper(n int) string {
return strFromSrc(n, upperBytes)
}
func StrLetterNum(n int) string {
return strFromSrc(n, letterNumsBytes)
}
func StrLetterNumUpper(n int) string {
return strFromSrc(n, letterNumsUpperBytes)
}