惯用JS加密编码算法 二：Base64编码,解码函数

二：Base64编码,解码函数

var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; 
var 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); 

function base64encode(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 += base64EncodeChars.charAt(c1 >> 2); 
        out += base64EncodeChars.charAt((c1 & 0x3) << 4); 
        out += "=="; 
        break; 
    } 
    c2 = str.charCodeAt(i++); 
    if(i == len) 
    { 
        out += base64EncodeChars.charAt(c1 >> 2); 
        out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4)); 
        out += base64EncodeChars.charAt((c2 & 0xF) << 2); 
        out += "="; 
        break; 
    } 
    c3 = str.charCodeAt(i++); 
    out += base64EncodeChars.charAt(c1 >> 2); 
    out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4)); 
    out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6)); 
    out += base64EncodeChars.charAt(c3 & 0x3F); 
    } 
    return out; 
} 

function base64decode(str) { 
    var c1, c2, c3, c4; 
    var i, len, out; 

    len = str.length; 
    i = 0; 
    out = ""; 
    while(i < len) { 
    /* c1 */ 
    do { 
        c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff]; 
    } while(i < len && c1 == -1); 
    if(c1 == -1) 
        break; 

    /* c2 */ 
    do { 
        c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff]; 
    } while(i < len && c2 == -1); 
    if(c2 == -1) 
        break; 

    out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4)); 

    /* c3 */ 
    do { 
        c3 = str.charCodeAt(i++) & 0xff; 
        if(c3 == 61) 
        return out; 
        c3 = base64DecodeChars[c3]; 
    } while(i < len && c3 == -1); 
    if(c3 == -1) 
        break; 

    out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2)); 

    /* c4 */ 
    do { 
        c4 = str.charCodeAt(i++) & 0xff; 
        if(c4 == 61) 
        return out; 
        c4 = base64DecodeChars[c4]; 
    } while(i < len && c4 == -1); 
    if(c4 == -1) 
        break; 
    out += String.fromCharCode(((c3 & 0x03) << 6) | c4); 
    } 
    return out; 
} 

function utf16to8(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; 
} 

function utf8to16(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; 
} 


function doit() { 
    var f = document.f 
    f.output.value = base64encode(utf16to8(f.source.value)) 
    f.decode.value = utf8to16(base64decode(f.output.value)) 
} 

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