gitee.com/hongliu9527/go-tools@v0.0.8/string_tool/rand.go (about)

     1  package string_tool
     2  
     3  import (
     4  	"math/rand"
     5  	"time"
     6  	"unsafe"
     7  )
     8  
     9  const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    10  const (
    11  	letterIdxBits = 6                    // 6 bits to represent a letter index
    12  	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
    13  	letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
    14  )
    15  
    16  func RandString(n int) string {
    17  	src := rand.NewSource(time.Now().UnixNano())
    18  
    19  	b := make([]byte, n)
    20  	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
    21  	for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
    22  		if remain == 0 {
    23  			cache, remain = src.Int63(), letterIdxMax
    24  		}
    25  		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
    26  			b[i] = letterBytes[idx]
    27  			i--
    28  		}
    29  		cache >>= letterIdxBits
    30  		remain--
    31  	}
    32  
    33  	return *(*string)(unsafe.Pointer(&b))
    34  }