79 lines
1.6 KiB
Go
79 lines
1.6 KiB
Go
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// Copyright (c) 2013-2014 Conformal Systems LLC.
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package base58
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import (
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"math/big"
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"strings"
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)
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// alphabet is the modified base58 alphabet used by Bitcoin.
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const alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
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var bigRadix = big.NewInt(58)
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var bigZero = big.NewInt(0)
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// Decode decodes a modified base58 string to a byte slice.
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func Decode(b string) []byte {
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answer := big.NewInt(0)
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j := big.NewInt(1)
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for i := len(b) - 1; i >= 0; i-- {
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tmp := strings.IndexAny(alphabet, string(b[i]))
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if tmp == -1 {
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return []byte("")
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}
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idx := big.NewInt(int64(tmp))
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tmp1 := big.NewInt(0)
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tmp1.Mul(j, idx)
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answer.Add(answer, tmp1)
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j.Mul(j, bigRadix)
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}
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tmpval := answer.Bytes()
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var numZeros int
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for numZeros = 0; numZeros < len(b); numZeros++ {
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if b[numZeros] != alphabet[0] {
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break
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}
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}
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flen := numZeros + len(tmpval)
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val := make([]byte, flen, flen)
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copy(val[numZeros:], tmpval)
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return val
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}
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// Encode encodes a byte slice to a modified base58 string.
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func Encode(b []byte) string {
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x := new(big.Int)
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x.SetBytes(b)
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answer := make([]byte, 0, len(b)*136/100)
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for x.Cmp(bigZero) > 0 {
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mod := new(big.Int)
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x.DivMod(x, bigRadix, mod)
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answer = append(answer, alphabet[mod.Int64()])
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}
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// leading zero bytes
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for _, i := range b {
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if i != 0 {
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break
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}
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answer = append(answer, alphabet[0])
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}
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// reverse
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alen := len(answer)
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for i := 0; i < alen/2; i++ {
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answer[i], answer[alen-1-i] = answer[alen-1-i], answer[i]
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}
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return string(answer)
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}
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