CRC calculations

gistfile1.php

	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;
	}