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80 lines
1.6 KiB
Go
80 lines
1.6 KiB
Go
package stringx
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import (
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crand "crypto/rand"
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"fmt"
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"math/rand"
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"sync"
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"time"
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)
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const (
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letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
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letterIdxBits = 6 // 6 bits to represent a letter index
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idLen = 8
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defaultRandLen = 8
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letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
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letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
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)
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var src = newLockedSource(time.Now().UnixNano())
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type lockedSource struct {
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source rand.Source
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lock sync.Mutex
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}
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func newLockedSource(seed int64) *lockedSource {
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return &lockedSource{
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source: rand.NewSource(seed),
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}
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}
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func (ls *lockedSource) Int63() int64 {
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ls.lock.Lock()
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defer ls.lock.Unlock()
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return ls.source.Int63()
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}
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func (ls *lockedSource) Seed(seed int64) {
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ls.lock.Lock()
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defer ls.lock.Unlock()
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ls.source.Seed(seed)
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}
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func Rand() string {
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return Randn(defaultRandLen)
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}
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func RandId() string {
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b := make([]byte, idLen)
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_, err := crand.Read(b)
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if err != nil {
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return Randn(idLen)
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}
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return fmt.Sprintf("%x%x%x%x", b[0:2], b[2:4], b[4:6], b[6:8])
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}
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func Randn(n int) string {
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b := make([]byte, n)
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// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
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for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
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if remain == 0 {
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cache, remain = src.Int63(), letterIdxMax
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}
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if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
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b[i] = letterBytes[idx]
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i--
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}
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cache >>= letterIdxBits
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remain--
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}
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return string(b)
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}
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func Seed(seed int64) {
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src.Seed(seed)
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}
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