var BASE64={
    /**
     * This variable is coded key, each character corresponds to the subscript it represents the coding
     */
    enKey: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
    /**
     * This variable is the decoding key, is an array, 
     * BASE64 character's ASCII value to do the next standard, 
     * which corresponds to is represented by the character encoding value.
     */
    deKey: new Array(
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
        52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
        -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
        15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
        -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
        41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1
    ),
    /**
     * Encode
     */
    encode: function(src){
        //Use an array to store the encoded characters, the efficiency is much higher than string concatenation.
        var str=new Array();
        var ch1, ch2, ch3;
        var pos=0;
       //Encoding each of the three characters.
        while(pos+3<=src.length){
            ch1=src.charCodeAt(pos++);
            ch2=src.charCodeAt(pos++);
            ch3=src.charCodeAt(pos++);
            str.push(this.enKey.charAt(ch1>>2), this.enKey.charAt(((ch1<<4)+(ch2>>4))&0x3f));
            str.push(this.enKey.charAt(((ch2<<2)+(ch3>>6))&0x3f), this.enKey.charAt(ch3&0x3f));
        }
        //Encoding the rest of the characters
        if(pos<src.length){
            ch1=src.charCodeAt(pos++);
            str.push(this.enKey.charAt(ch1>>2));
            if(pos<src.length){
                ch2=src.charCodeAt(pos);
                str.push(this.enKey.charAt(((ch1<<4)+(ch2>>4))&0x3f));
                str.push(this.enKey.charAt(ch2<<2&0x3f), '=');
            }else{
                str.push(this.enKey.charAt(ch1<<4&0x3f), '==');
            }
        }
       //Combination of the encoded character, save as a string.
        return str.join('');
    },
    /**
     * Decode
     */
    decode: function(src){
        //Use an array to store the decoded characters.
        var str=new Array();
        var ch1, ch2, ch3, ch4;
        var pos=0;
       //Filtering illegal characters and remove the '='.
        src=src.replace(/[^A-Za-z0-9\+\/]/g, '');
        //Decoding the source string in partition of per four characters.
        while(pos+4<=src.length){
            ch1=this.deKey[src.charCodeAt(pos++)];
            ch2=this.deKey[src.charCodeAt(pos++)];
            ch3=this.deKey[src.charCodeAt(pos++)];
            ch4=this.deKey[src.charCodeAt(pos++)];
            str.push(String.fromCharCode(
                (ch1<<2&0xff)+(ch2>>4), (ch2<<4&0xff)+(ch3>>2), (ch3<<6&0xff)+ch4));
        }
        //Decode the rest of the characters
        if(pos+1<src.length){
            ch1=this.deKey[src.charCodeAt(pos++)];
            ch2=this.deKey[src.charCodeAt(pos++)];
            if(pos<src.length){
                ch3=this.deKey[src.charCodeAt(pos)];
                str.push(String.fromCharCode((ch1<<2&0xff)+(ch2>>4), (ch2<<4&0xff)+(ch3>>2)));
            }else{
                str.push(String.fromCharCode((ch1<<2&0xff)+(ch2>>4)));
            }
        }
       //Combination of the decoded characters, save as a string.
        return str.join('');
    }
};