note 54561 added to function.crc32

I think that Mario's (spectrumizer at cycos dot net) CRC16 algorithm might be wrong. At least according to these two online calculators: http://www.zorc.breitbandkatze.de/crc.html http://www.lammertbies.nl/comm/info/crc-calculation.html However, it seems that there can be some confusion concerning "official" CRC16 algorithms. See this article for two possible CRC16-CCITT algorithms: http://www.joegeluso.com/software/articles/ccitt.htm Here is a php implementation of the "bad" CRC16-CCITT algorithm from the article. The "bad" implementation might not match the "official" algorithm, but is widely used, including by the two crc calculators mentioned above. Note that crc16-CCITT is also referred to as crc16c. <?php // this function is used to calculate the (common) crc16c for an entire buffer function calculate_common_crc16c($buffer) { $crc16c = 0xffff; // the crc initial value $buffer_length = strlen($buffer); for ($i = 0; $i < $buffer_length; $i++) { $ch = ord($buffer[$i]); $crc16c = update_common_crc16c($ch, $crc16c); } return $crc16c; } // this function is used to calculate the (common) crc16c byte by byte // $ch is the next byte and $crc16c is the result from the last call, or 0xffff initially function update_common_crc16c($ch, $crc16c) { global $crc16c_polynomial; // This comment was in the code from // http://www.joegeluso.com/software/articles/ccitt.htm // Why are they shifting this byte left by 8 bits?? // How do the low bits of the poly ever see it? $ch <<= 8; for($i = 0; $i < 8; $i++) { if (($crc16c ^ $ch) & 0x8000) { $xor_flag = true; } else { $xor_flag = false; } $crc16c = $crc16c << 1; if ($xor_flag) { $crc16c = $crc16c ^ $crc16c_polynomial; } $ch = $ch << 1; } // mask off (zero out) the upper two bytes $crc16c = $crc16c & 0x0000ffff; return $crc16c; } ?> ---- Manual Page -- http://www.php.net/manual/en/function.crc32.php Edit -- http://master.php.net/manage/user-notes.php?action=edit+54561 Delete: added to the manual -- http://master.php.net/manage/user-notes.php?action=delete+54561&report=yes&reason=added+to+the+manual Delete: bad code -- http://master.php.net/manage/user-notes.php?action=delete+54561&report=yes&reason=bad+code Delete: spam -- http://master.php.net/manage/user-notes.php?action=delete+54561&report=yes&reason=spam Delete: useless -- http://master.php.net/manage/user-notes.php?action=delete+54561&report=yes&reason=useless Delete: non-english -- http://master.php.net/manage/user-notes.php?action=delete+54561&report=yes&reason=non-english Delete: other reasons -- http://master.php.net/manage/user-notes.php?action=delete+54561&report=yes Reject -- http://master.php.net/manage/user-notes.php?action=reject+54561&report=yes Search -- http://master.php.net/manage/user-notes.php