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aadsm on 04/10/10

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Last Edited at 04/10/10 04:05pm

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Read a UTF8 String from a "byte" source

/ Published in: JavaScript

This is useful if you have a string where each character represents a byte like the one returned by getStringAt() in BinaryAjax.

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function readUTF8String(bytes) {
    var ix = 0;
 
    if( bytes.slice(0,3) == "\xEF\xBB\xBF") {
        ix = 3;
    }
 
    var string = "";
    for( ; ix < bytes.length; ix++ ) {
        var byte1 = bytes[ix].charCodeAt(0);
        if( byte1 < 0x80 ) {
            string += String.fromCharCode(byte1);
        } else if( byte1 >= 0xC2 && byte1 < 0xE0 ) {
            var byte2 = bytes[++ix].charCodeAt(0);
            string += String.fromCharCode(((byte1&0x1F)<<6) + (byte2&0x3F));
        } else if( byte1 >= 0xE0 && byte1 < 0xF0 ) {
            var byte2 = bytes[++ix].charCodeAt(0);
            var byte3 = bytes[++ix].charCodeAt(0);
            string += String.fromCharCode(((byte1&0xFF)<<12) + ((byte2&0x3F)<<6) + (byte3&0x3F));
        } else if( byte1 >= 0xF0 && byte1 < 0xF5) {
            var byte2 = bytes[++ix].charCodeAt(0);
            var byte3 = bytes[++ix].charCodeAt(0);
            var byte4 = bytes[++ix].charCodeAt(0);
            var codepoint = ((byte1&0x07)<<18) + ((byte2&0x3F)<<12)+ ((byte3&0x3F)<<6) + (byte4&0x3F);
            codepoint -= 0x10000;
            string += String.fromCharCode(
                (codepoint>>10) + 0xD800,
                (codepoint&0x3FF) + 0xDC00
            );
        }
    }
 
    return string;
}

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