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|
package base36
import (
"math"
"math/big"
"strings"
)
var (
base36 = []byte{
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z'}
index = map[byte]int{
'0': 0, '1': 1, '2': 2, '3': 3, '4': 4,
'5': 5, '6': 6, '7': 7, '8': 8, '9': 9,
'A': 10, 'B': 11, 'C': 12, 'D': 13, 'E': 14,
'F': 15, 'G': 16, 'H': 17, 'I': 18, 'J': 19,
'K': 20, 'L': 21, 'M': 22, 'N': 23, 'O': 24,
'P': 25, 'Q': 26, 'R': 27, 'S': 28, 'T': 29,
'U': 30, 'V': 31, 'W': 32, 'X': 33, 'Y': 34,
'Z': 35,
'a': 10, 'b': 11, 'c': 12, 'd': 13, 'e': 14,
'f': 15, 'g': 16, 'h': 17, 'i': 18, 'j': 19,
'k': 20, 'l': 21, 'm': 22, 'n': 23, 'o': 24,
'p': 25, 'q': 26, 'r': 27, 's': 28, 't': 29,
'u': 30, 'v': 31, 'w': 32, 'x': 33, 'y': 34,
'z': 35,
}
)
// Encode encodes a number to base36.
func Encode(value uint64) string {
var res [16]byte
var i int
for i = len(res) - 1; value != 0; i-- {
res[i] = base36[value%36]
value /= 36
}
return string(res[i+1:])
}
// Decode decodes a base36-encoded string.
func Decode(s string) uint64 {
res := uint64(0)
l := len(s) - 1
for idx := range s {
c := s[l-idx]
res += uint64(index[c]) * uint64(math.Pow(36, float64(idx)))
}
return res
}
var bigRadix = big.NewInt(36)
var bigZero = big.NewInt(0)
// EncodeBytesAsBytes encodes a byte slice to base36.
func EncodeBytesAsBytes(b []byte) []byte {
x := new(big.Int)
x.SetBytes(b)
answer := make([]byte, 0, len(b)*136/100)
for x.Cmp(bigZero) > 0 {
mod := new(big.Int)
x.DivMod(x, bigRadix, mod)
answer = append(answer, base36[mod.Int64()])
}
// leading zero bytes
for _, i := range b {
if i != 0 {
break
}
answer = append(answer, base36[0])
}
// reverse
alen := len(answer)
for i := 0; i < alen/2; i++ {
answer[i], answer[alen-1-i] = answer[alen-1-i], answer[i]
}
return answer
}
// EncodeBytes encodes a byte slice to base36 string.
func EncodeBytes(b []byte) string {
return string(EncodeBytesAsBytes(b))
}
// DecodeToBytes decodes a base36 string to a byte slice, using alphabet.
func DecodeToBytes(b string) []byte {
alphabet := string(base36)
answer := big.NewInt(0)
j := big.NewInt(1)
for i := len(b) - 1; i >= 0; i-- {
tmp := strings.IndexAny(alphabet, string(b[i]))
if tmp == -1 {
return []byte("")
}
idx := big.NewInt(int64(tmp))
tmp1 := big.NewInt(0)
tmp1.Mul(j, idx)
answer.Add(answer, tmp1)
j.Mul(j, bigRadix)
}
tmpval := answer.Bytes()
var numZeros int
for numZeros = 0; numZeros < len(b); numZeros++ {
if b[numZeros] != alphabet[0] {
break
}
}
flen := numZeros + len(tmpval)
val := make([]byte, flen, flen)
copy(val[numZeros:], tmpval)
return val
}
|
