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<?php |
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declare(strict_types=1); |
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namespace PBurggraf\CRC; |
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/** |
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* @author Philip Burggraf <[email protected]> |
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*/ |
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abstract class AbstractCRC |
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{ |
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protected int $poly; |
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protected int $init; |
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protected bool $reverseIn; |
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protected bool $reverseOut; |
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protected int $xorOut; |
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protected int $bitLength; |
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public function calculate(string $buffer): int |
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{ |
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$bufferLength = \strlen($buffer); |
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$mask = (((1 << ($this->bitLength - 1)) - 1) << 1) | 1; |
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$highBit = 1 << ($this->bitLength - 1); |
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$crc = $this->init; |
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for ($iterator = 0; $iterator < $bufferLength; ++$iterator) { |
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$character = \ord($buffer[$iterator]); |
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if ($this->reverseIn) { |
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$character = $this->binaryReverse($character, 8); |
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} |
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for ($j = 0x80; $j; $j >>= 1) { |
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$bit = $crc & $highBit; |
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$crc <<= 1; |
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if ($character & $j) { |
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$bit ^= $highBit; |
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} |
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if ($bit) { |
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$crc ^= $this->poly; |
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} |
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} |
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} |
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if ($this->reverseOut) { |
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$crc = $this->binaryReverse($crc, $this->bitLength); |
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} |
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$crc ^= $this->xorOut; |
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return $crc & $mask; |
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} |
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public function calculateWithTable(string $buffer, array $table): int |
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{ |
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$bufferLength = \strlen($buffer); |
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if (count($table) !== 256) { |
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throw new \InvalidArgumentException('CRC lookup table not populated'); |
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} |
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$mask = (((1 << ($this->bitLength - 1)) - 1) << 1) | 1; |
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$highBit = 1 << ($this->bitLength - 1); |
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$crc = $this->init; |
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for ($iterator = 0; $iterator < $bufferLength; ++$iterator) { |
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$character = \ord($buffer[$iterator]); |
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if ($this->reverseIn) { |
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$character = $this->binaryReverse($character, 8); |
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} |
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$tableValue = $table[(($crc >> ($this->bitLength - 8)) ^ $character) & 0xFF]; |
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if (($this->bitLength - 8) !== 0) { |
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$tableValue ^= ($crc << 8); |
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} |
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$crc = $tableValue; |
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$crc &= $mask; |
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} |
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if ($this->reverseOut) { |
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$crc = $this->binaryReverse($crc, $this->bitLength); |
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} |
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$crc ^= $this->xorOut; |
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return $crc & $mask; |
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} |
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/** |
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* @return int[] |
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*/ |
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public function populateTable(): array |
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{ |
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$tableSize = 256; |
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$mask = (((1 << ($this->bitLength - 1)) - 1) << 1) | 1; |
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$highBit = 1 << ($this->bitLength - 1); |
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$table = []; |
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for ($iterator = 0; $iterator < $tableSize; ++$iterator) { |
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$temp = 0; |
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$a = ($iterator << ($this->bitLength - 8)); |
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for ($j = 0; $j < 8; ++$j) { |
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if ((($temp ^ $a) & $highBit) !== 0) { |
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$temp = (($temp << 1) ^ $this->poly); |
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} else { |
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$temp <<= 1; |
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} |
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$a <<= 1; |
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} |
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$table[$iterator] = $temp & $mask; |
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} |
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return $table; |
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} |
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protected function binaryReverse(int $binaryInput, int $bitlen): int |
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{ |
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$cloneBits = $binaryInput; |
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$binaryInput = 0; |
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$count = 0; |
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while ($count < $bitlen) { |
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++$count; |
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$binaryInput <<= 1; |
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$binaryInput |= ($cloneBits & 0x1); |
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$cloneBits >>= 1; |
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} |
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return $binaryInput; |
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} |
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} |
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pburggraf /
CRC
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