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发信人: thinkin (强强), 信区: Linux
标  题: Binary pattern match
发信站: BBS 水木清华站 (Thu Feb 17 11:00:01 2000)

<?
function findfiletype($filename) {
     /*
       The array with the filetype and pattern, separate with a semi-colon.
       Each pair in the pattern represents a single byte in the input file.
       The question mark is used to match a single digit but should be used
on
       both digits in the byte pair. Originally made to find the filetype of

       an input file uploaded using the POST method, which explains the "non
e"
       comparison.
       - Petter Nilsen <pettern@thule.no>,
    */
    $types = array(
         "zip;$504B",
         "lha;$????2D6C68",
         "gif;$47494638??",
         "jpg;$????????????4A464946",
         "exe;$4D5A",
         "bmp;$424D"
    );
    $len = 0;
    $match = 0;
    $ext =  "";
    if($filename ==  "none") {
        return($ext);
    }
    $fh = fopen($filename,  "r");
    if($fh) {
        $tmpBuf = fread($fh, 250);
        if(strlen($tmpBuf) == 250) {
            for($iOffset = 0; $types[$iOffset]; $iOffset += 1) {
                list($ext,$pattern,$junk) = explode(  ";",$types[$iOffset]);

                $len = strlen($pattern);
                if($pattern[0] ==  '$') {
                    for($n = 1; $n < $len; $n += 2) {
                        $lowval = 0; $highval = 0;
                        if($pattern[$n] ==  '?' || $pattern[$n + 1] ==  '?')

                            continue;
                        $highval = Ord($pattern[$n])  - 48;
                        if($highval > 9) {
                            $highval -= 7;
                        }
                        $lowval = Ord($pattern[$n + 1]) - 48;
                        if($lowval > 9) {
                            $lowval -= 7;
                        }
                        if(Ord($tmpBuf[($n - 1) >> 1]) == (($highval << 4) +
$lowval)) {
                            $match = 1;
                        }
                        else {
                            $match = 0;
                            break;
                        }
                    }
                    if($match) {
                        break;
                    }
                }
            }
        }
        if(!$match) {
            $ext =  "";
        }
        fclose($fh);
    }
    return ($ext);
}
?>
--

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