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JavaScript实现的Base64编码和解码

<SCRIPT>
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;
}

alert(base64encode("?"))
</script>

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