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<?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.
*/
private const FORMAT_INFO_MASK_QR = 0x5412;
/**
* Lookup table for decoding format information.
*
* See ISO 18004:2006, Annex C, Table C.1
*/
private const FORMAT_INFO_DECODE_LOOKUP = [
[0x5412, 0x00],
[0x5125, 0x01],
[0x5e7c, 0x02],
[0x5b4b, 0x03],
[0x45f9, 0x04],
[0x40ce, 0x05],
[0x4f97, 0x06],
[0x4aa0, 0x07],
[0x77c4, 0x08],
[0x72f3, 0x09],
[0x7daa, 0x0a],
[0x789d, 0x0b],
[0x662f, 0x0c],
[0x6318, 0x0d],
[0x6c41, 0x0e],
[0x6976, 0x0f],
[0x1689, 0x10],
[0x13be, 0x11],
[0x1ce7, 0x12],
[0x19d0, 0x13],
[0x0762, 0x14],
[0x0255, 0x15],
[0x0d0c, 0x16],
[0x083b, 0x17],
[0x355f, 0x18],
[0x3068, 0x19],
[0x3f31, 0x1a],
[0x3a06, 0x1b],
[0x24b4, 0x1c],
[0x2183, 0x1d],
[0x2eda, 0x1e],
[0x2bed, 0x1f],
];
/**
* Offset i holds the number of 1 bits in the binary representation of i.
*
* @var array
*/
private const BITS_SET_IN_HALF_BYTE = [0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4];
/**
* Error correction level.
*
* @var ErrorCorrectionLevel
*/
private $ecLevel;
/**
* Data mask.
*
* @var int
*/
private $dataMask;
protected function __construct(int $formatInfo)
{
$this->ecLevel = ErrorCorrectionLevel::forBits(($formatInfo >> 3) & 0x3);
$this->dataMask = $formatInfo & 0x7;
}
/**
* Checks how many bits are different between two integers.
*/
public static function numBitsDiffering(int $a, int $b) : int
{
$a ^= $b;
return (
self::BITS_SET_IN_HALF_BYTE[$a & 0xf]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 4) & 0xf)]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 8) & 0xf)]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 12) & 0xf)]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 16) & 0xf)]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 20) & 0xf)]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 24) & 0xf)]
+ self::BITS_SET_IN_HALF_BYTE[(BitUtils::unsignedRightShift($a, 28) & 0xf)]
);
}
/**
* Decodes format information.
*/
public static function decodeFormatInformation(int $maskedFormatInfo1, int $maskedFormatInfo2) : ?self
{
$formatInfo = self::doDecodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2);
if (null !== $formatInfo) {
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.
*/
private static function doDecodeFormatInformation(int $maskedFormatInfo1, int $maskedFormatInfo2) : ?self
{
$bestDifference = PHP_INT_MAX;
$bestFormatInfo = 0;
foreach (self::FORMAT_INFO_DECODE_LOOKUP 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;
}
/**
* Returns the error correction level.
*/
public function getErrorCorrectionLevel() : ErrorCorrectionLevel
{
return $this->ecLevel;
}
/**
* Returns the data mask.
*/
public function getDataMask() : int
{
return $this->dataMask;
}
/**
* Hashes the code of the EC level.
*/
public function hashCode() : int
{
return ($this->ecLevel->getBits() << 3) | $this->dataMask;
}
/**
* Verifies if this instance equals another one.
*/
public function equals(self $other) : bool
{
return (
$this->ecLevel === $other->ecLevel
&& $this->dataMask === $other->dataMask
);
}
}
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