bitcoinjs-lib/src/base58.js

(function (Bitcoin) {
  Bitcoin.Base58 = {
    alphabet: "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz",
    validRegex: /^[1-9A-HJ-NP-Za-km-z]+$/,
    base: BigInteger.valueOf(58),

    /**
     * Convert a byte array to a base58-encoded string.
     *
     * Written by Mike Hearn for BitcoinJ.
     *   Copyright (c) 2011 Google Inc.
     *
     * Ported to JavaScript by Stefan Thomas.
     */
    encode: function (input) {
      var bi = BigInteger.fromByteArrayUnsigned(input);
      var chars = [];

      while (bi.compareTo(B58.base) >= 0) {
        var mod = bi.mod(B58.base);
        chars.unshift(B58.alphabet[mod.intValue()]);
        bi = bi.subtract(mod).divide(B58.base);
      }
      chars.unshift(B58.alphabet[bi.intValue()]);

      // Convert leading zeros too.
      for (var i = 0; i < input.length; i++) {
        if (input[i] == 0x00) {
          chars.unshift(B58.alphabet[0]);
        } else break;
      }

      return chars.join('');
    },

    /**
     * Convert a base58-encoded string to a byte array.
     *
     * Written by Mike Hearn for BitcoinJ.
     *   Copyright (c) 2011 Google Inc.
     *
     * Ported to JavaScript by Stefan Thomas.
     */
    decode: function (input) {
      var bi = BigInteger.valueOf(0);
      var leadingZerosNum = 0;
      for (var i = input.length - 1; i >= 0; i--) {
        var alphaIndex = B58.alphabet.indexOf(input[i]);
        if (alphaIndex < 0) {
          throw "Invalid character";
        }	
        bi = bi.add(BigInteger.valueOf(alphaIndex)
                    .multiply(B58.base.pow(input.length - 1 -i)));

        // This counts leading zero bytes
        if (input[i] == "1") leadingZerosNum++;
        else leadingZerosNum = 0;
      }
      var bytes = bi.toByteArrayUnsigned();

      // Add leading zeros
      while (leadingZerosNum-- > 0) bytes.unshift(0);

      return bytes;
    }
  };

  var B58 = Bitcoin.Base58;
})(
  'undefined' != typeof Bitcoin ? Bitcoin : module.exports
);