/**  
*  
*  base64 encode / decode  
*  文字采用utf-8方式进行base64编码
*  
*/  
    
function base64() {   
    
    // private property   
    _keystr = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456789+/=";   
    
    // public method for encoding   
    this.encode = function (input) {   
        var output = "";   
        var chr1, chr2, chr3, enc1, enc2, enc3, enc4;   
        var i = 0;   
        input = _utf8_encode(input);   
        while (i < input.length) {   
            chr1 = input.charcodeat(i++);   
            chr2 = input.charcodeat(i++);   
            chr3 = input.charcodeat(i++);   
            enc1 = chr1 >> 2;   
            enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);   
            enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);   
            enc4 = chr3 & 63;   
            if (isnan(chr2)) {   
                enc3 = enc4 = 64;   
            } else if (isnan(chr3)) {   
                enc4 = 64;   
            }   
            output = output +   
            _keystr.charat(enc1) + _keystr.charat(enc2) +   
            _keystr.charat(enc3) + _keystr.charat(enc4);   
        }   
        return output;   
    }   
    
    // public method for decoding   
    this.decode = function (input) {   
        var output = "";   
        var chr1, chr2, chr3;   
        var enc1, enc2, enc3, enc4;   
        var i = 0;   
        input = input.replace(/[^a-za-z0-9\+\/\=]/g, "");   
        while (i < input.length) {   
            enc1 = _keystr.indexof(input.charat(i++));   
            enc2 = _keystr.indexof(input.charat(i++));   
            enc3 = _keystr.indexof(input.charat(i++));   
            enc4 = _keystr.indexof(input.charat(i++));   
            chr1 = (enc1 << 2) | (enc2 >> 4);   
            chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);   
            chr3 = ((enc3 & 3) << 6) | enc4;   
            output = output + string.fromcharcode(chr1);   
            if (enc3 != 64) {   
                output = output + string.fromcharcode(chr2);   
            }   
            if (enc4 != 64) {   
                output = output + string.fromcharcode(chr3);   
            }   
        }   
        output = _utf8_decode(output);   
        return output;   
    }   
    
    // private method for utf-8 encoding   
    _utf8_encode = function (string) {   
        string = string.replace(/\r\n/g,"\n");   
        var utftext = "";   
        for (var n = 0; n < string.length; n++) {   
            var c = string.charcodeat(n);   
            if (c < 128) {   
                utftext += string.fromcharcode(c);   
            } else if((c > 127) && (c < 2048)) {   
                utftext += string.fromcharcode((c >> 6) | 192);   
                utftext += string.fromcharcode((c & 63) | 128);   
            } else {   
                utftext += string.fromcharcode((c >> 12) | 224);   
                utftext += string.fromcharcode(((c >> 6) & 63) | 128);   
                utftext += string.fromcharcode((c & 63) | 128);   
            }   
    
        }   
        return utftext;   
    }   
    
    // private method for utf-8 decoding   
    _utf8_decode = function (utftext) {   
        var string = "";   
        var i = 0;   
        var c = c1 = c2 = 0;   
        while ( i < utftext.length ) {   
            c = utftext.charcodeat(i);   
            if (c < 128) {   
                string += string.fromcharcode(c);   
                i++;   
            } else if((c > 191) && (c < 224)) {   
                c2 = utftext.charcodeat(i+1);   
                string += string.fromcharcode(((c & 31) << 6) | (c2 & 63));   
                i += 2;   
            } else {   
                c2 = utftext.charcodeat(i+1);   
                c3 = utftext.charcodeat(i+2);   
                string += string.fromcharcode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));   
                i += 3;   
            }   
        }   
        return string;   
    }   
}