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utilBase58.go
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// Copyright (c) 2023 gpress Authors.
//
// This file is part of gpress.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package main
import (
"math/big"
)
var bigRadix = big.NewInt(58)
var bigZero = big.NewInt(0)
// base58Decode decodes a modified base58 string to a byte slice.
func base58Decode(b string) []byte {
answer := big.NewInt(0)
j := big.NewInt(1)
scratch := new(big.Int)
for i := len(b) - 1; i >= 0; i-- {
tmp := b58[b[i]]
if tmp == 255 {
return []byte("")
}
scratch.SetInt64(int64(tmp))
scratch.Mul(j, scratch)
answer.Add(answer, scratch)
j.Mul(j, bigRadix)
}
tmpval := answer.Bytes()
var numZeros int
for numZeros = 0; numZeros < len(b); numZeros++ {
if b[numZeros] != alphabetIdx0 {
break
}
}
flen := numZeros + len(tmpval)
val := make([]byte, flen)
copy(val[numZeros:], tmpval)
return val
}
// base58Encode encodes a byte slice to a modified base58 string.
func base58Encode(b []byte) string {
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, alphabet[mod.Int64()])
}
// leading zero bytes
for _, i := range b {
if i != 0 {
break
}
answer = append(answer, alphabetIdx0)
}
// reverse
alen := len(answer)
for i := 0; i < alen/2; i++ {
answer[i], answer[alen-1-i] = answer[alen-1-i], answer[i]
}
return string(answer)
}
const (
// alphabet is the modified base58 alphabet used by Bitcoin.
alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
alphabetIdx0 = '1'
)
var b58 = [256]byte{
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 0, 1, 2, 3, 4, 5, 6,
7, 8, 255, 255, 255, 255, 255, 255,
255, 9, 10, 11, 12, 13, 14, 15,
16, 255, 17, 18, 19, 20, 21, 255,
22, 23, 24, 25, 26, 27, 28, 29,
30, 31, 32, 255, 255, 255, 255, 255,
255, 33, 34, 35, 36, 37, 38, 39,
40, 41, 42, 43, 255, 44, 45, 46,
47, 48, 49, 50, 51, 52, 53, 54,
55, 56, 57, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255,
}