define(function(require, exports, module) {
  
  var code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".split(""); //索引表
  
  /**
   * @author laixiangran@163.com
   * @description 将二进制序列转换为Base64编码
   * @param {String}
   * @return {String}
   */
  function binToBase64(bitString) {
    var result = "";
    var tail = bitString.length % 6;
    var bitStringTemp1 = bitString.substr(0, bitString.length - tail);
    var bitStringTemp2 = bitString.substr(bitString.length - tail, tail);
    for (var i = 0; i < bitStringTemp1.length; i += 6) {
      var index = parseInt(bitStringTemp1.substr(i, 6), 2);
      result += code[index];
    }
    bitStringTemp2 += new Array(7 - tail).join("0");
    if (tail) {
      result += code[parseInt(bitStringTemp2, 2)];
      result += new Array((6 - tail) / 2 + 1).join("=");
    }
    return result;
  }
  
  /**
   * @author laixiangran@163.com
   * @description 将base64编码转换为二进制序列
   * @param {String}
   * @return {String}
   */
  function base64ToBin(str) {
    var bitString = "";
    var tail = 0;
    for (var i = 0; i < str.length; i++) {
      if (str[i] != "=") {
        var decode = code.indexOf(str[i]).toString(2);
        bitString += (new Array(7 - decode.length)).join("0") + decode;
      } else {
        tail++;
      }
    }
    return bitString.substr(0, bitString.length - tail * 2);
  }
  
  /**
   * @author laixiangran@163.com
   * @description 将字符转换为二进制序列
   * @param {String} str
   * @return {String}  
   */
  function stringToBin(str) {
    var result = "";
    for (var i = 0; i < str.length; i++) {
      var charCode = str.charCodeAt(i).toString(2);
      result += (new Array(9 - charCode.length).join("0") + charCode);
    }
    return result;
  }
 
  /**
   * @author laixiangran@163.com
   * @description 将二进制序列转换为字符串
   * @param {String} Bin
   */
  function BinToStr(Bin) {
    var result = "";
    for (var i = 0; i < Bin.length; i += 8) {
      result += String.fromCharCode(parseInt(Bin.substr(i, 8), 2));
    }
    return result;
  }
 
  exports.decodeBase64 = function(str) {
    return BinToStr(base64ToBin(str));
  }
  exports.encodeBase64 = function(str) {
    return binToBase64(stringToBin(str));
  }
})