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// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
package utils
import (
"crypto/rand"
"math"
"math/big"
"github.com/ALTree/bigfloat"
"github.com/google/uuid"
)
const (
ESCAPE_CODE_SAFE_ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~ "
HUMAN_ALPHABET = "23456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
)
func num_to_string(number *big.Int, alphabet []rune, alphabet_len *big.Int, pad_to_length int) string {
var zero, digit big.Int
if number.Sign() < 0 {
*number = zero
}
capacity := 64
if pad_to_length > capacity {
capacity = pad_to_length
}
ans := make([]rune, 0, capacity)
for number.Cmp(&zero) == 1 {
number.DivMod(number, alphabet_len, &digit)
ans = append(ans, alphabet[digit.Uint64()])
}
al := len(ans)
if pad_to_length > -1 && al < pad_to_length {
ans = ans[:pad_to_length]
for i := al; i < pad_to_length; i++ {
ans[i] = alphabet[0]
}
}
return string(ans)
}
func get_padding_length(alphabet_len int) int {
bi := big.NewInt(2)
bi = bi.Exp(bi, big.NewInt(128), nil)
bb := new(big.Float).SetPrec(256)
bb.SetInt(bi)
log_al := bigfloat.Log(big.NewFloat(float64(alphabet_len)).SetPrec(256))
log_b := bigfloat.Log(bb)
res := new(big.Float).SetPrec(256)
res = res.Quo(log_b, log_al)
val, _ := res.Float64()
return int(math.Ceil(val))
}
type ShortUUID struct {
alphabet []rune
alphabet_len big.Int
pad_to_length int
}
func CreateShortUUID(alphabet string) *ShortUUID {
if alphabet == "" {
alphabet = HUMAN_ALPHABET
}
var ans = ShortUUID{
alphabet: []rune(alphabet),
}
ans.pad_to_length = get_padding_length(len(ans.alphabet))
ans.alphabet_len.SetUint64(uint64(len(ans.alphabet)))
return &ans
}
func (self *ShortUUID) Random(num_bits int64) (string, error) {
max := big.NewInt(0).Exp(big.NewInt(2), big.NewInt(num_bits), nil)
bi, err := rand.Int(rand.Reader, max)
if err != nil {
return "", err
}
return num_to_string(bi, self.alphabet, &self.alphabet_len, self.pad_to_length), nil
}
func (self *ShortUUID) Uuid4() (string, error) {
b, err := uuid.NewRandom()
if err != nil {
return "", err
}
bb, err := b.MarshalBinary()
if err != nil {
return "", err
}
var bi big.Int
bi.SetBytes(bb)
return num_to_string(&bi, self.alphabet, &self.alphabet_len, self.pad_to_length), nil
}
var HumanUUID *ShortUUID
func HumanUUID4() (string, error) {
if HumanUUID == nil {
HumanUUID = CreateShortUUID(HUMAN_ALPHABET)
}
return HumanUUID.Uuid4()
}
func HumanRandomId(num_bits int64) (string, error) {
if HumanUUID == nil {
HumanUUID = CreateShortUUID(HUMAN_ALPHABET)
}
return HumanUUID.Random(num_bits)
}
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