
    /*
    编码规则

    Base64编码的思想是是采用64个基本的ASCII码字符对数据进行重新编码。
    它将需要编码的数据拆分成字节数组。
    以3个字节为一组。按顺序排列24 位数据，再把这24位数据分成4组，即每组6位。
    再在每组的的最高位前补两个0凑足一个字节。
    这样就把一个3字节为一组的数据重新编码成了4个字节。
    当所要编码的数据的字节数不是3的整倍数，
    也就是说在分组时最后一组不够3个字节。
    这时在最后一组填充1到2个0字节。
    并在最后编码完成后在结尾添加1到2个 “=”。 

    */
var  Base64 = {

        //下面是64个基本的编码
        base64EncodeChars: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
        base64DecodeChars: 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),
        //编码的方法
        base64encode: function (str) {
            var out, i, len;
            var c1, c2, c3;
            len = str.length;
            i = 0;
            out = "";
            while (i < len) {
                c1 = str.charCodeAt(i++) & 0xff;
                if (i == len) {
                    out += Base64.base64EncodeChars.charAt(c1 >> 2);
                    out += Base64.base64EncodeChars.charAt((c1 & 0x3) << 4);
                    out += "==";
                    break;
                }
                c2 = str.charCodeAt(i++);
                if (i == len) {
                    out += Base64.base64EncodeChars.charAt(c1 >> 2);
                    out += Base64.base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
                    out += Base64.base64EncodeChars.charAt((c2 & 0xF) << 2);
                    out += "=";
                    break;
                }
                c3 = str.charCodeAt(i++);
                out += Base64.base64EncodeChars.charAt(c1 >> 2);
                out += Base64.base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
                out += Base64.base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
                out += Base64.base64EncodeChars.charAt(c3 & 0x3F);
            }
            return out;
        },

        //解码的方法
        base64decode: function (str) {
            var c1, c2, c3, c4;
            var i, len, out;
            len = str.length;
            i = 0;
            out = "";
            while (i < len) {
                do {
                    c1 = Base64.base64DecodeChars[str.charCodeAt(i++) & 0xff];
                } while (i < len && c1 == -1);
                if (c1 == -1)
                    break;
                do {
                    c2 = Base64.base64DecodeChars[str.charCodeAt(i++) & 0xff];
                } while (i < len && c2 == -1);
                if (c2 == -1)
                    break;
                out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
                do {
                    c3 = str.charCodeAt(i++) & 0xff;
                    if (c3 == 61)
                        return out;
                    c3 = Base64.base64DecodeChars[c3];
                } while (i < len && c3 == -1);
                if (c3 == -1)
                    break;
                out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
                do {
                    c4 = str.charCodeAt(i++) & 0xff;
                    if (c4 == 61)
                        return out;
                    c4 = Base64.base64DecodeChars[c4];
                } while (i < len && c4 == -1);
                if (c4 == -1)
                    break;
                out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
            }
            return out;
        },

        utf16to8: function (str) {
            var out, i, len, c;
            out = "";
            len = str.length;
            for (i = 0; i < len; i++) {
                c = str.charCodeAt(i);
                if ((c >= 0x0001) && (c <= 0x007F)) {
                    out += str.charAt(i);
                } else if (c > 0x07FF) {
                    out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
                    out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));
                    out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
                } else {
                    out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));
                    out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
                }
            }
            return out;
        },

        utf8to16: function (str) {
            var out, i, len, c;
            var char2, char3;
            out = "";
            len = str.length;
            i = 0;
            while (i < len) {
                c = str.charCodeAt(i++);
                switch (c >> 4) {
                    case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
                        // 0xxxxxxx
                        out += str.charAt(i - 1);
                        break;
                    case 12: case 13:
                        // 110x xxxx   10xx xxxx
                        char2 = str.charCodeAt(i++);
                        out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
                        break;
                    case 14:
                        // 1110 xxxx  10xx xxxx  10xx xxxx
                        char2 = str.charCodeAt(i++);
                        char3 = str.charCodeAt(i++);
                        out += String.fromCharCode(((c & 0x0F) << 12) |
                       ((char2 & 0x3F) << 6) |
                       ((char3 & 0x3F) << 0));
                        break;
                }
            }
            return out;
        }, //end
        encode: function (input) {
            return Base64.base64encode(Base64.utf16to8(input));
        },
        decode: function (str) {
            return Base64.utf8to16(Base64.base64decode(input))
        }


    };