note 31832 added to function.crc32

I needed the crc32 of a file that was pretty large, so I didn't want to read it into memory. So I made this: <?php $GLOBALS['__crc32_table']=array(); // Lookup table array __crc32_init_table(); function __crc32_init_table() { // Builds lookup table array // This is the official polynomial used by // CRC-32 in PKZip, WinZip and Ethernet. $polynomial = 0x04c11db7; // 256 values representing ASCII character codes. for($i=0;$i <= 0xFF;++$i) { $GLOBALS['__crc32_table'][$i]=(__crc32_reflect($i,8) << 24); for($j=0;$j < 8;++$j) { $GLOBALS['__crc32_table'][$i]=(($GLOBALS['__crc32_table'][$i] << 1) ^ (($GLOBALS['__crc32_table'][$i] & (1 << 31))?$polynomial:0)); } $GLOBALS['__crc32_table'][$i] = __crc32_reflect($GLOBALS['__crc32_table'][$i], 32); } } function __crc32_reflect($ref, $ch) { // Reflects CRC bits in the lookup table $value=0; // Swap bit 0 for bit 7, bit 1 for bit 6, etc. for($i=1;$i<($ch+1);++$i) { if($ref & 1) $value |= (1 << ($ch-$i)); $ref = (($ref >> 1) & 0x7fffffff); } return $value; } function __crc32_string($text) { // Creates a CRC from a text string // Once the lookup table has been filled in by the two functions above, // this function creates all CRCs using only the lookup table. // You need unsigned variables because negative values // introduce high bits where zero bits are required. // PHP doesn't have unsigned integers: // I've solved this problem by doing a '&' after a '>>'. // Start out with all bits set high. $crc=0xffffffff; $len=strlen($text); // Perform the algorithm on each character in the string, // using the lookup table values. for($i=0;$i < $len;++$i) { $crc=(($crc >> 8) & 0x00ffffff) ^ $GLOBALS['__crc32_table'][($crc & 0xFF) ^ ord($text{$i})]; } // Exclusive OR the result with the beginning value. return $crc ^ 0xffffffff; } function __crc32_file($name) { // Creates a CRC from a file // Info: look at __crc32_string // Start out with all bits set high. $crc=0xffffffff; if(($fp=fopen($name,'rb'))===false) return false; // Perform the algorithm on each character in file for(;;) { $i=@fread($fp,1); if(strlen($i)==0) break; $crc=(($crc >> 8) & 0x00ffffff) ^ $GLOBALS['__crc32_table'][($crc & 0xFF) ^ ord($i)]; } @fclose($fp); // Exclusive OR the result with the beginning value. return $crc ^ 0xffffffff; } ?> -- http://www.php.net/manual/en/function.crc32.php http://master.php.net/manage/user-notes.php?action=edit+31832 http://master.php.net/manage/user-notes.php?action=delete+31832 http://master.php.net/manage/user-notes.php?action=reject+31832