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random.go
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random.go
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/*
* Copyright (c) 2019. Abstrium SAS <team (at) pydio.com>
* This file is part of Pydio Cells.
*
* Pydio Cells is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Pydio Cells is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with Pydio Cells. If not, see <http://www.gnu.org/licenses/>.
*
* The latest code can be found at <https://pydio.com>.
*/
// Package std provides tools for standard types (strings, int, floats, etc).
package std
import (
"math/rand"
"sync"
"time"
)
const letterBytes = "abcdefghijklmnpqrstuvwxyz123456789ABCDEFGHIJKLMNPQRSTUVWXYZ"
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())
randMutex = &sync.Mutex{}
)
// Random [m,n]
func getRandomSource() rand.Source {
randMutex.Lock()
defer randMutex.Unlock()
return src
}
// Randkey produces a random string with a given length
func Randkey(n int) string {
b := make([]byte, n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, getRandomSource().Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = getRandomSource().Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}