BaconQrCode
| FormatInformation | Encapsulates a QR Code's format information, including the data mask used and error correction level. |
<?php
/**
* BaconQrCode
*
* @link http://github.com/Bacon/BaconQrCode For the canonical source repository
* @copyright 2013 Ben 'DASPRiD' Scholzen
* @license http://opensource.org/licenses/BSD-2-Clause Simplified BSD License
*/
namespace BaconQrCode\Common;
/**
* Encapsulates a QR Code's format information, including the data mask used and
* error correction level.
*/
class FormatInformation
{
/**
* Mask for format information.
*/
const FORMAT_INFO_MASK_QR = 0x5412;
/**
* Lookup table for decoding format information.
*
* See ISO 18004:2006, Annex C, Table C.1
*
* @var array
*/
protected static $formatInfoDecodeLookup = array(
array(0x5412, 0x00),
array(0x5125, 0x01),
array(0x5e7c, 0x02),
array(0x5b4b, 0x03),
array(0x45f9, 0x04),
array(0x40ce, 0x05),
array(0x4f97, 0x06),
array(0x4aa0, 0x07),
array(0x77c4, 0x08),
array(0x72f3, 0x09),
array(0x7daa, 0x0a),
array(0x789d, 0x0b),
array(0x662f, 0x0c),
array(0x6318, 0x0d),
array(0x6c41, 0x0e),
array(0x6976, 0x0f),
array(0x1689, 0x10),
array(0x13be, 0x11),
array(0x1ce7, 0x12),
array(0x19d0, 0x13),
array(0x0762, 0x14),
array(0x0255, 0x15),
array(0x0d0c, 0x16),
array(0x083b, 0x17),
array(0x355f, 0x18),
array(0x3068, 0x19),
array(0x3f31, 0x1a),
array(0x3a06, 0x1b),
array(0x24b4, 0x1c),
array(0x2183, 0x1d),
array(0x2eda, 0x1e),
array(0x2bed, 0x1f),
);
/**
* Offset i holds the number of 1 bits in the binary representation of i.
*
* @var array
*/
protected static $bitsSetInHalfByte = array(0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4);
/**
* Error correction level.
*
* @var ErrorCorrectionLevel
*/
protected $ecLevel;
/**
* Data mask.
*
* @var integer
*/
protected $dataMask;
/**
* Creates a new format information instance.
*
* @param integer $formatInfo
*/
protected function __construct($formatInfo)
{
$this->ecLevel = new ErrorCorrectionLevel(($formatInfo >> 3) & 0x3);
$this->dataMask = $formatInfo & 0x7;
}
/**
* Checks how many bits are different between two integers.
*
* @param integer $a
* @param integer $b
* @return integer
*/
public static function numBitsDiffering($a, $b)
{
$a ^= $b;
return (
self::$bitsSetInHalfByte[$a & 0xf]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 4) & 0xf)]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 8) & 0xf)]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 12) & 0xf)]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 16) & 0xf)]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 20) & 0xf)]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 24) & 0xf)]
+ self::$bitsSetInHalfByte[(BitUtils::unsignedRightShift($a, 28) & 0xf)]
);
}
/**
* Decodes format information.
*
* @param integer $maskedFormatInfo1
* @param integer $maskedFormatInfo2
* @return FormatInformation|null
*/
public static function decodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2)
{
$formatInfo = self::doDecodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2);
if ($formatInfo !== null) {
return $formatInfo;
}
// Should return null, but, some QR codes apparently do not mask this
// info. Try again by actually masking the pattern first.
return self::doDecodeFormatInformation(
$maskedFormatInfo1 ^ self::FORMAT_INFO_MASK_QR,
$maskedFormatInfo2 ^ self::FORMAT_INFO_MASK_QR
);
}
/**
* Internal method for decoding format information.
*
* @param integer $maskedFormatInfo1
* @param integer $maskedFormatInfo2
* @return FormatInformation|null
*/
protected static function doDecodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2)
{
$bestDifference = PHP_INT_MAX;
$bestFormatInfo = 0;
foreach (self::$formatInfoDecodeLookup as $decodeInfo) {
$targetInfo = $decodeInfo[0];
if ($targetInfo === $maskedFormatInfo1 || $targetInfo === $maskedFormatInfo2) {
// Found an exact match
return new self($decodeInfo[1]);
}
$bitsDifference = self::numBitsDiffering($maskedFormatInfo1, $targetInfo);
if ($bitsDifference < $bestDifference) {
$bestFormatInfo = $decodeInfo[1];
$bestDifference = $bitsDifference;
}
if ($maskedFormatInfo1 !== $maskedFormatInfo2) {
// Also try the other option
$bitsDifference = self::numBitsDiffering($maskedFormatInfo2, $targetInfo);
if ($bitsDifference < $bestDifference) {
$bestFormatInfo = $decodeInfo[1];
$bestDifference = $bitsDifference;
}
}
}
// Hamming distance of the 32 masked codes is 7, by construction, so
// <= 3 bits differing means we found a match.
if ($bestDifference <= 3) {
return new self($bestFormatInfo);
}
return null;
}
/**
* Gets the error correction level.
*
* @return ErrorCorrectionLevel
*/
public function getErrorCorrectionLevel()
{
return $this->ecLevel;
}
/**
* Gets the data mask.
*
* @return integer
*/
public function getDataMask()
{
return $this->dataMask;
}
/**
* Hashes the code of the EC level.
*
* @return integer
*/
public function hashCode()
{
return ($this->ecLevel->get() << 3) | $this->dataMask;
}
/**
* Verifies if this instance equals another one.
*
* @param mixed $other
* @return boolean
*/
public function equals($other) {
if (!$other instanceof self) {
return false;
}
return (
$this->ecLevel->get() === $other->getErrorCorrectionLevel()->get()
&& $this->dataMask === $other->getDataMask()
);
}
}