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base58.go
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base58.go
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//Copyright (c) 2012 Tommi Virtanen
//Permission is hereby granted, free of charge, to any person obtaining a copy
//of this software and associated documentation files (the "Software"), to deal
//in the Software without restriction, including without limitation the rights
//to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//copies of the Software, and to permit persons to whom the Software is
//furnished to do so, subject to the following conditions:
//
//The above copyright notice and this permission notice shall be included in
//all copies or substantial portions of the Software.
//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//THE SOFTWARE.
// Package base58 implements a human-friendly base58 encoding.
//
// As opposed to base64 and friends, base58 is typically used to
// convert integers. You can use big.Int.SetBytes to convert arbitrary
// bytes to an integer first, and big.Int.Bytes the other way around.
package base58
import (
"math/big"
"strconv"
)
const alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
var decodeMap [256]byte
func init() {
for i := 0; i < len(decodeMap); i++ {
decodeMap[i] = 0xFF
}
for i := 0; i < len(alphabet); i++ {
decodeMap[alphabet[i]] = byte(i)
}
}
//CorruptInputError representds input is corrupted.
type CorruptInputError int64
//Error is to implement Error interface.
func (e CorruptInputError) Error() string {
return "illegal base58 data at input byte " + strconv.FormatInt(int64(e), 10)
}
// DecodeToBig a big integer from the bytes. Returns an error on corrupt
// input.
func DecodeToBig(src []byte) (*big.Int, error) {
n := new(big.Int)
radix := big.NewInt(58)
for i := 0; i < len(src); i++ {
b := decodeMap[src[i]]
if b == 0xFF {
return nil, CorruptInputError(i)
}
n.Mul(n, radix)
n.Add(n, big.NewInt(int64(b)))
}
return n, nil
}
// EncodeBig encodes src, appending to dst. Be sure to use the returned
// new value of dst.
func EncodeBig(dst []byte, src *big.Int) []byte {
start := len(dst)
n := new(big.Int)
n.Set(src)
radix := big.NewInt(58)
zero := big.NewInt(0)
for n.Cmp(zero) > 0 {
mod := new(big.Int)
n.DivMod(n, radix, mod)
dst = append(dst, alphabet[mod.Int64()])
}
for i, j := start, len(dst)-1; i < j; i, j = i+1, j-1 {
dst[i], dst[j] = dst[j], dst[i]
}
return dst
}