base64.js

/**
 *create by 2014年7月9日 http://javascript.css-js.com/
 *BASE64 Encode and Decode By UTF-8 unicode
 *可以和java的BASE64编码和解码互相转化
 */
 
    var BASE64_MAPPING = [
        'A','B','C','D','E','F','G','H',
        'I','J','K','L','M','N','O','P',
        'Q','R','S','T','U','V','W','X',
        'Y','Z','a','b','c','d','e','f',
        'g','h','i','j','k','l','m','n',
        'o','p','q','r','s','t','u','v',
        'w','x','y','z','0','1','2','3',
        '4','5','6','7','8','9','+','/'
    ];
 
    /**
     *ascii convert to binary
     */
    var _toBinary = function(ascii){
        var binary = new Array();
        while(ascii > 0){
            var b = ascii%2;
            ascii = Math.floor(ascii/2);
            binary.push(b);
        }
        /*
        var len = binary.length;
        if(6-len > 0){
            for(var i = 6-len ; i > 0 ; --i){
                binary.push(0);
            }
        }*/
        binary.reverse();
        return binary;
    };
 
    /**
     *binary convert to decimal
     */
    var _toDecimal  = function(binary){
        var dec = 0;
        var p = 0;
        for(var i = binary.length-1 ; i >= 0 ; --i){
            var b = binary[i];
            if(b == 1){
                dec += Math.pow(2 , p);
            }
            ++p;
        }
        return dec;
    };
 
    /**
     *unicode convert to utf-8
     */
    var _toUTF8Binary = function(c , binaryArray){
        var mustLen = (8-(c+1)) + ((c-1)*6);
        var fatLen = binaryArray.length;
        var diff = mustLen - fatLen;
        while(--diff >= 0){
            binaryArray.unshift(0);
        }
        var binary = [];
        var _c = c;
        while(--_c >= 0){
            binary.push(1);
        }
        binary.push(0);
        var i = 0 , len = 8 - (c+1);
        for(; i < len ; ++i){
            binary.push(binaryArray[i]);
        }
 
        for(var j = 0 ; j < c-1 ; ++j){
            binary.push(1);
            binary.push(0);
            var sum = 6;
            while(--sum >= 0){
                binary.push(binaryArray[i++]);
            }
        }
        return binary;
    };
 
    var BASE64 = {
            /**
             *BASE64 Encode
             */
            encoder:function(str){
                var base64_Index = [];
                var binaryArray = [];
                for(var i = 0 , len = str.length ; i < len ; ++i){
                    var unicode = str.charCodeAt(i);
                    var _tmpBinary = _toBinary(unicode);
                    if(unicode < 0x80){
                        var _tmpdiff = 8 - _tmpBinary.length;
                        while(--_tmpdiff >= 0){
                            _tmpBinary.unshift(0);
                        }
                        binaryArray = binaryArray.concat(_tmpBinary);
                    }else if(unicode >= 0x80 && unicode <= 0x7FF){
                        binaryArray = binaryArray.concat(_toUTF8Binary(2 , _tmpBinary));
                    }else if(unicode >= 0x800 && unicode <= 0xFFFF){//UTF-8 3byte
                        binaryArray = binaryArray.concat(_toUTF8Binary(3 , _tmpBinary));
                    }else if(unicode >= 0x10000 && unicode <= 0x1FFFFF){//UTF-8 4byte
                        binaryArray = binaryArray.concat(_toUTF8Binary(4 , _tmpBinary));    
                    }else if(unicode >= 0x200000 && unicode <= 0x3FFFFFF){//UTF-8 5byte
                        binaryArray = binaryArray.concat(_toUTF8Binary(5 , _tmpBinary));
                    }else if(unicode >= 4000000 && unicode <= 0x7FFFFFFF){//UTF-8 6byte
                        binaryArray = binaryArray.concat(_toUTF8Binary(6 , _tmpBinary));
                    }
                }
 
                var extra_Zero_Count = 0;
                for(var i = 0 , len = binaryArray.length ; i < len ; i+=6){
                    var diff = (i+6)-len;
                    if(diff == 2){
                        extra_Zero_Count = 2;
                    }else if(diff == 4){
                        extra_Zero_Count = 4;
                    }
                    //if(extra_Zero_Count > 0){
                    //  len += extra_Zero_Count+1;
                    //}
                    var _tmpExtra_Zero_Count = extra_Zero_Count;
                    while(--_tmpExtra_Zero_Count >= 0){
                        binaryArray.push(0);
                    }
                    base64_Index.push(_toDecimal(binaryArray.slice(i , i+6)));
                }
 
                var base64 = '';
                for(var i = 0 , len = base64_Index.length ; i < len ; ++i){
                    base64 += BASE64_MAPPING[base64_Index[i]];
                }
 
                for(var i = 0 , len = extra_Zero_Count/2 ; i < len ; ++i){
                    base64 += '=';
                }
                return base64;
            },
            /**
             *BASE64  Decode for UTF-8 
             */
            decoder : function(_base64Str){
                var _len = _base64Str.length;
                var extra_Zero_Count = 0;
                /**
                 *计算在进行BASE64编码的时候，补了几个0
                 */
                if(_base64Str.charAt(_len-1) == '='){
                    //alert(_base64Str.charAt(_len-1));
                    //alert(_base64Str.charAt(_len-2));
                    if(_base64Str.charAt(_len-2) == '='){//两个等号说明补了4个0
                        extra_Zero_Count = 4;
                        _base64Str = _base64Str.substring(0 , _len-2);
                    }else{//一个等号说明补了2个0
                        extra_Zero_Count = 2;
                        _base64Str = _base64Str.substring(0 , _len - 1);
                    }
                }
 
                var binaryArray = [];
                for(var i = 0 , len = _base64Str.length; i < len ; ++i){
                    var c = _base64Str.charAt(i);
                    for(var j = 0 , size = BASE64_MAPPING.length ; j < size ; ++j){
                        if(c == BASE64_MAPPING[j]){
                            var _tmp = _toBinary(j);
                            /*不足6位的补0*/
                            var _tmpLen = _tmp.length;
                            if(6-_tmpLen > 0){
                                for(var k = 6-_tmpLen ; k > 0 ; --k){
                                    _tmp.unshift(0);
                                }
                            }
                            binaryArray = binaryArray.concat(_tmp);
                            break;
                        }
                    }
                }
 
                if(extra_Zero_Count > 0){
                    binaryArray = binaryArray.slice(0 , binaryArray.length - extra_Zero_Count);
                }
 
                var unicode = [];
                var unicodeBinary = [];
                for(var i = 0 , len = binaryArray.length ; i < len ; ){
                    if(binaryArray[i] == 0){
                        unicode=unicode.concat(_toDecimal(binaryArray.slice(i,i+8)));
                        i += 8;
                    }else{
                        var sum = 0;
                        while(i < len){
                            if(binaryArray[i] == 1){
                                ++sum;
                            }else{
                                break;
                            }
                            ++i;
                        }
                        unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+1 , i+8-sum));
                        i += 8 - sum;
                        while(sum > 1){
                            unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+2 , i+8));
                            i += 8;
                            --sum;
                        }
                        unicode = unicode.concat(_toDecimal(unicodeBinary));
                        unicodeBinary = [];
                    }
                }
                //---------直接转换为结果
                var strResult = '';  
                for(var i = 0 , len =  unicode.length ; i < len ;++i){  
                      strResult += String.fromCharCode(unicode[i]);  
                }
                return strResult;
            }
    };