goext/langext/base62.go

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2022-10-27 17:55:27 +02:00
package langext
import (
"crypto/rand"
"errors"
"math"
"math/big"
"strings"
)
var (
base62Base = uint64(62)
base62CharacterSet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
)
func RandBase62(rlen int) string {
bi52 := big.NewInt(int64(len(base62CharacterSet)))
randMax := big.NewInt(math.MaxInt64)
r := ""
for i := 0; i < rlen; i++ {
v, err := rand.Int(rand.Reader, randMax)
if err != nil {
panic(err)
}
r += string(base62CharacterSet[v.Mod(v, bi52).Int64()])
}
return r
}
func EncodeBase62(num uint64) string {
if num == 0 {
return "0"
}
b := make([]byte, 0)
// loop as long the num is bigger than zero
for num > 0 {
r := num % base62Base
num -= r
num /= base62Base
b = append([]byte{base62CharacterSet[int(r)]}, b...)
}
return string(b)
}
func DecodeBase62(str string) (uint64, error) {
if str == "" {
return 0, errors.New("empty string")
}
result := uint64(0)
for _, v := range str {
result *= base62Base
pos := strings.IndexRune(base62CharacterSet, v)
if pos == -1 {
return 0, errors.New("invalid character: " + string(v))
}
result += uint64(pos)
}
return result, nil
}