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CRC calculations - Циклический избыточный код (англ. Cyclic redundancy check, CRC) — алгоритм нахождения контрольной суммы, предназначенный для проверки целостности данных.
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| function crc16($string, $crc = 0) { | |
| for($x = 0; $x < strlen($string); $x++) { | |
| $crc = $crc ^ ord($string[$x]); | |
| echo $crc . '<br />'; | |
| for($y = 0; $y < 8; $y++) { | |
| if(($crc & 0x0001) == 0x0001) { | |
| $crc = (($crc >> 1) ^ 0x10589); | |
| } | |
| else { | |
| $crc = $crc >> 1; | |
| } | |
| } | |
| } | |
| return $crc; | |
| } | |
| function crc16_2($string) { | |
| $crc = 0; | |
| for($x = 0; $x < strlen($string); $x++) { | |
| $crc = $crc ^ ord($string[$x]); | |
| for($y = 0; $y < 8; $y++) { | |
| if(($crc & 0x0001) == 0x0001) { | |
| $crc = (($crc >> 1) ^ 0x8408); | |
| } | |
| else { | |
| $crc = $crc >> 1; | |
| } | |
| } | |
| } | |
| $lb = ($crc & 0xff00) >> 8; | |
| $hb = ($crc & 0x00ff) << 8; | |
| $crc = $hb | $lb; | |
| return $crc; | |
| } | |
| function crc16_3($data) { | |
| $crc = 0xFFFF; | |
| for($i = 0; $i < strlen($data); $i++) { | |
| $x = (($crc >> 8) ^ ord($data[$i])) & 0xFF; | |
| $x ^= $x >> 4; | |
| $crc = (($crc << 8) ^ ($x << 12) ^ ($x << 5) ^ $x) & 0xFFFF; | |
| } | |
| return $crc; | |
| } | |
| function crc16_4($string, $crc = 0) { | |
| for($x = 0; $x < strlen($string); $x++) { | |
| $crc = $crc ^ ord($string[$x]); | |
| for($y = 0; $y < 8; $y++) { | |
| if(($crc & 0x0001) == 0x0001) { | |
| $crc = (($crc >> 1) ^ 0xA001); | |
| } | |
| else { | |
| $crc = $crc >> 1; | |
| } | |
| } | |
| } | |
| return $crc; | |
| } | |
| function crc16_5($string) { | |
| $crc = 0xFFFF; | |
| for($x = 0; $x < strlen($string); $x++) { | |
| $crc = $crc ^ ord($string[$x]); | |
| for($y = 0; $y < 8; $y++) { | |
| if(($crc & 0x0001) == 0x0001) { | |
| $crc = (($crc >> 1) ^ 0xA001); | |
| } | |
| else { | |
| $crc = $crc >> 1; | |
| } | |
| } | |
| } | |
| return $crc; | |
| } | |
| function calculate_common_crc16c($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 $crc16c; | |
| } | |
| function update_common_crc16c($ch, $crc16c) { | |
| global $crc16c_polynomial; | |
| $ch <<= 8; | |
| for($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; | |
| } |
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