A PHP equivalent of Visual FoxPro SYS(2007) checksum CRC 16-bit.

sys2007-crc16.php

<?php
	function crc16( $str, $params = array() )
	{
		$defaults = array( 
			'initial_value'	=> 0xFFFF, 
			'polynomial'	=> 0x1021, // CRC-CCITT
			'xor_out'	=> 0, 
		); 
	
		foreach ( $defaults as $k => $v )
		{ 
			if ( ! isset($params[$k] ) ) $params[$k] = $v; 
		};
	
		$str .= ''; 
		$crc = $params['initial_value']; 
		$len = strlen( $str ); 
		$i = 0; 
	
		while ( $len-- )
		{ 
			$crc ^= ord( $str[$i++] ) << 8; 
			$crc &= 0xFFFF; 
			
			for ( $j = 0; $j < 8; $j+=1 )
			{ 
				$crc = ( $crc & 0x8000 ) ? ( $crc << 1 ) ^ $params['polynomial'] : $crc << 1; 
				$crc &= 0xFFFF;
			};
		};
	
		$crc ^= $params['xor_out']; 
		
		return $crc; 
	};
?>