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package base58
import (
"fmt"
"math/big"
)
var (
bn0 = big.NewInt(0)
bn58 = big.NewInt(58)
)
// TrivialBase58Encoding encodes the passed bytes into a base58 encoded string
// (inefficiently).
func TrivialBase58Encoding(a []byte) string {
return TrivialBase58EncodingAlphabet(a, BTCAlphabet)
}
// TrivialBase58EncodingAlphabet encodes the passed bytes into a base58 encoded
// string (inefficiently) with the passed alphabet.
func TrivialBase58EncodingAlphabet(a []byte, alphabet *Alphabet) string {
zero := alphabet.encode[0]
idx := len(a)*138/100 + 1
buf := make([]byte, idx)
bn := new(big.Int).SetBytes(a)
var mo *big.Int
for bn.Cmp(bn0) != 0 {
bn, mo = bn.DivMod(bn, bn58, new(big.Int))
idx--
buf[idx] = alphabet.encode[mo.Int64()]
}
for i := range a {
if a[i] != 0 {
break
}
idx--
buf[idx] = zero
}
return string(buf[idx:])
}
// TrivialBase58Decoding decodes the base58 encoded bytes (inefficiently).
func TrivialBase58Decoding(str string) ([]byte, error) {
return TrivialBase58DecodingAlphabet(str, BTCAlphabet)
}
// TrivialBase58DecodingAlphabet decodes the base58 encoded bytes
// (inefficiently) using the given b58 alphabet.
func TrivialBase58DecodingAlphabet(str string, alphabet *Alphabet) ([]byte, error) {
zero := alphabet.encode[0]
var zcount int
for i := 0; i < len(str) && str[i] == zero; i++ {
zcount++
}
leading := make([]byte, zcount)
var padChar rune = -1
src := []byte(str)
j := 0
for ; j < len(src) && src[j] == byte(padChar); j++ {
}
n := new(big.Int)
for i := range src[j:] {
c := alphabet.decode[src[i]]
if c == -1 {
return nil, fmt.Errorf("illegal base58 data at input index: %d", i)
}
n.Mul(n, bn58)
n.Add(n, big.NewInt(int64(c)))
}
return append(leading, n.Bytes()...), nil
}
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