base58.go raw

   1  package base58
   2  
   3  import (
   4  	"math/big"
   5  )
   6  
   7  var bigRadix = big.NewInt(58)
   8  var bigZero = big.NewInt(0)
   9  
  10  // Decode decodes a modified base58 string to a byte slice.
  11  func Decode(b string) []byte {
  12  	answer := big.NewInt(0)
  13  	j := big.NewInt(1)
  14  	scratch := new(big.Int)
  15  	for i := len(b) - 1; i >= 0; i-- {
  16  		tmp := b58[b[i]]
  17  		if tmp == 255 {
  18  			return []byte("")
  19  		}
  20  		scratch.SetInt64(int64(tmp))
  21  		scratch.Mul(j, scratch)
  22  		answer.Add(answer, scratch)
  23  		j.Mul(j, bigRadix)
  24  	}
  25  	tmpval := answer.Bytes()
  26  	var numZeros int
  27  	for numZeros = 0; numZeros < len(b); numZeros++ {
  28  		if b[numZeros] != alphabetIdx0 {
  29  			break
  30  		}
  31  	}
  32  	flen := numZeros + len(tmpval)
  33  	val := make([]byte, flen)
  34  	copy(val[numZeros:], tmpval)
  35  	return val
  36  }
  37  
  38  // Encode encodes a byte slice to a modified base58 string.
  39  func Encode(b []byte) string {
  40  	x := new(big.Int)
  41  	x.SetBytes(b)
  42  	answer := make([]byte, 0, len(b)*136/100)
  43  	for x.Cmp(bigZero) > 0 {
  44  		mod := new(big.Int)
  45  		x.DivMod(x, bigRadix, mod)
  46  		answer = append(answer, alphabet[mod.Int64()])
  47  	}
  48  	// leading zero bytes
  49  	for _, i := range b {
  50  		if i != 0 {
  51  			break
  52  		}
  53  		answer = append(answer, alphabetIdx0)
  54  	}
  55  	// reverse
  56  	alen := len(answer)
  57  	for i := 0; i < alen/2; i++ {
  58  		answer[i], answer[alen-1-i] = answer[alen-1-i], answer[i]
  59  	}
  60  	return string(answer)
  61  }
  62