54 lines
1.4 KiB
Go
54 lines
1.4 KiB
Go
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package random
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import (
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"math/rand"
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"time"
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"unsafe"
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)
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const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
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const upperBytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
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const letterNumsBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
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const letterNumsUpperBytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
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const (
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letterIdxBits = 6 // 6 bits to represent a letter index
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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 = rand.NewSource(time.Now().UnixNano())
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func strFromSrc(n int, srcChars string) 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(srcChars) {
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b[i] = srcChars[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)(unsafe.Pointer(&b))
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}
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func Str(n int) string {
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return strFromSrc(n, letterBytes)
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}
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func StrUpper(n int) string {
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return strFromSrc(n, upperBytes)
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}
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func StrLetterNum(n int) string {
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return strFromSrc(n, letterNumsBytes)
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}
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func StrLetterNumUpper(n int) string {
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return strFromSrc(n, letterNumsUpperBytes)
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}
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