Reads the bits in the {@link BitMatrix} representing the finder pattern in the * correct order in order to reconstruct the codewords bytes contained within the * QR Code.
* * @return array bytes encoded within the QR Code * @throws \RuntimeException if the exact number of bytes expected is not read */ public function readCodewords():array{ $formatInfo = $this->readFormatInformation(); $version = $this->readVersion(); // Get the data mask for the format used in this QR Code. This will exclude // some bits from reading as we wind through the bit matrix. $dimension = $this->bitMatrix->getDimension(); $this->bitMatrix->unmask($dimension, $formatInfo->getDataMask()); $functionPattern = $this->bitMatrix->buildFunctionPattern($version); $readingUp = true; $result = []; $resultOffset = 0; $currentByte = 0; $bitsRead = 0; // Read columns in pairs, from right to left for($j = $dimension - 1; $j > 0; $j -= 2){ if($j === 6){ // Skip whole column with vertical alignment pattern; // saves time and makes the other code proceed more cleanly $j--; } // Read alternatingly from bottom to top then top to bottom for($count = 0; $count < $dimension; $count++){ $i = $readingUp ? $dimension - 1 - $count : $count; for($col = 0; $col < 2; $col++){ // Ignore bits covered by the function pattern if(!$functionPattern->get($j - $col, $i)){ // Read a bit $bitsRead++; $currentByte <<= 1; if($this->bitMatrix->get($j - $col, $i)){ $currentByte |= 1; } // If we've made a whole byte, save it off if($bitsRead === 8){ $result[$resultOffset++] = $currentByte; //(byte) $bitsRead = 0; $currentByte = 0; } } } } $readingUp = !$readingUp; // switch directions } if($resultOffset !== $version->getTotalCodewords()){ throw new RuntimeException('offset differs from total codewords for version'); } return $result; } /** *Reads format information from one of its two locations within the QR Code.
* * @return \chillerlan\QRCode\Common\FormatInformation encapsulating the QR Code's format info * @throws \RuntimeException if both format information locations cannot be parsed as * the valid encoding of format information */ public function readFormatInformation():FormatInformation{ if($this->parsedFormatInfo !== null){ return $this->parsedFormatInfo; } // Read top-left format info bits $formatInfoBits1 = 0; for($i = 0; $i < 6; $i++){ $formatInfoBits1 = $this->copyBit($i, 8, $formatInfoBits1); } // .. and skip a bit in the timing pattern ... $formatInfoBits1 = $this->copyBit(7, 8, $formatInfoBits1); $formatInfoBits1 = $this->copyBit(8, 8, $formatInfoBits1); $formatInfoBits1 = $this->copyBit(8, 7, $formatInfoBits1); // .. and skip a bit in the timing pattern ... for($j = 5; $j >= 0; $j--){ $formatInfoBits1 = $this->copyBit(8, $j, $formatInfoBits1); } // Read the top-right/bottom-left pattern too $dimension = $this->bitMatrix->getDimension(); $formatInfoBits2 = 0; $jMin = $dimension - 7; for($j = $dimension - 1; $j >= $jMin; $j--){ $formatInfoBits2 = $this->copyBit(8, $j, $formatInfoBits2); } for($i = $dimension - 8; $i < $dimension; $i++){ $formatInfoBits2 = $this->copyBit($i, 8, $formatInfoBits2); } $this->parsedFormatInfo = $this->doDecodeFormatInformation($formatInfoBits1, $formatInfoBits2); if($this->parsedFormatInfo !== null){ return $this->parsedFormatInfo; } // Should return null, but, some QR codes apparently do not mask this info. // Try again by actually masking the pattern first. $this->parsedFormatInfo = $this->doDecodeFormatInformation( $formatInfoBits1 ^ FormatInformation::MASK_QR, $formatInfoBits2 ^ FormatInformation::MASK_QR ); if($this->parsedFormatInfo !== null){ return $this->parsedFormatInfo; } throw new RuntimeException('failed to read format info'); } /** * @param int $maskedFormatInfo1 format info indicator, with mask still applied * @param int $maskedFormatInfo2 second copy of same info; both are checked at the same time * to establish best match * * @return \chillerlan\QRCode\Common\FormatInformation|null information about the format it specifies, or null * if doesn't seem to match any known pattern */ private function doDecodeFormatInformation(int $maskedFormatInfo1, int $maskedFormatInfo2):?FormatInformation{ // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing $bestDifference = PHP_INT_MAX; $bestFormatInfo = 0; foreach(FormatInformation::DECODE_LOOKUP as $decodeInfo){ [$maskedBits, $dataBits] = $decodeInfo; if($maskedFormatInfo1 === $dataBits || $maskedFormatInfo2 === $dataBits){ // Found an exact match return new FormatInformation($maskedBits); } $bitsDifference = self::numBitsDiffering($maskedFormatInfo1, $dataBits); if($bitsDifference < $bestDifference){ $bestFormatInfo = $maskedBits; $bestDifference = $bitsDifference; } if($maskedFormatInfo1 !== $maskedFormatInfo2){ // also try the other option $bitsDifference = self::numBitsDiffering($maskedFormatInfo2, $dataBits); if($bitsDifference < $bestDifference){ $bestFormatInfo = $maskedBits; $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 FormatInformation($bestFormatInfo); } return null; } /** *Reads version information from one of its two locations within the QR Code.
* * @return \chillerlan\QRCode\Common\Version encapsulating the QR Code's version * @throws \RuntimeException if both version information locations cannot be parsed as * the valid encoding of version information */ public function readVersion():Version{ if($this->parsedVersion !== null){ return $this->parsedVersion; } $dimension = $this->bitMatrix->getDimension(); $provisionalVersion = ($dimension - 17) / 4; if($provisionalVersion <= 6){ return new Version($provisionalVersion); } // Read top-right version info: 3 wide by 6 tall $versionBits = 0; $ijMin = $dimension - 11; for($j = 5; $j >= 0; $j--){ for($i = $dimension - 9; $i >= $ijMin; $i--){ $versionBits = $this->copyBit($i, $j, $versionBits); } } $this->parsedVersion = $this->decodeVersionInformation($versionBits); if($this->parsedVersion !== null && $this->parsedVersion->getDimension() === $dimension){ return $this->parsedVersion; } // Hmm, failed. Try bottom left: 6 wide by 3 tall $versionBits = 0; for($i = 5; $i >= 0; $i--){ for($j = $dimension - 9; $j >= $ijMin; $j--){ $versionBits = $this->copyBit($i, $j, $versionBits); } } $this->parsedVersion = $this->decodeVersionInformation($versionBits); if($this->parsedVersion !== null && $this->parsedVersion->getDimension() === $dimension){ return $this->parsedVersion; } throw new RuntimeException('failed to read version'); } /** * @param int $versionBits * * @return \chillerlan\QRCode\Common\Version|null */ private function decodeVersionInformation(int $versionBits):?Version{ $bestDifference = PHP_INT_MAX; $bestVersion = 0; for($i = 7; $i <= 40; $i++){ $targetVersion = new Version($i); $targetVersionPattern = $targetVersion->getVersionPattern(); // Do the version info bits match exactly? done. if($targetVersionPattern === $versionBits){ return $targetVersion; } // Otherwise see if this is the closest to a real version info bit string // we have seen so far /** @phan-suppress-next-line PhanTypeMismatchArgumentNullable ($targetVersionPattern is never null here) */ $bitsDifference = self::numBitsDiffering($versionBits, $targetVersionPattern); if($bitsDifference < $bestDifference){ $bestVersion = $i; $bestDifference = $bitsDifference; } } // We can tolerate up to 3 bits of error since no two version info codewords will // differ in less than 8 bits. if($bestDifference <= 3){ return new Version($bestVersion); } // If we didn't find a close enough match, fail return null; } public static function uRShift(int $a, int $b):int{ if($b === 0){ return $a; } return ($a >> $b) & ~((1 << (8 * PHP_INT_SIZE - 1)) >> ($b - 1)); } private static function numBitsDiffering(int $a, int $b):int{ // a now has a 1 bit exactly where its bit differs with b's $a ^= $b; // Offset i holds the number of 1 bits in the binary representation of i $BITS_SET_IN_HALF_BYTE = [0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4]; // Count bits set quickly with a series of lookups: $count = 0; for($i = 0; $i < 32; $i += 4){ $count += $BITS_SET_IN_HALF_BYTE[self::uRShift($a, $i) & 0x0F]; } return $count; } }