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<?php |
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declare(strict_types=1); |
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namespace SPSS; |
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/** |
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* Class ByteCodeCompressor |
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* Abstracts bytecode (de)compression |
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* @package SPSS |
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*/ |
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class ByteCodeReader |
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{ |
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private const BYTE_SYS_MISSING = 255; |
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private const BYTE_SPACES = 254; |
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private const BYTE_LITERAL = 253; |
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private const BYTE_NUL = 0; |
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/** @var Buffer */ |
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private $buffer; |
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private $commandBuffer = []; |
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private $dataBuffer = ''; |
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public function __construct(Buffer $buffer) |
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{ |
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$this->buffer = $buffer; |
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} |
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private function readBlock(): string |
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{ |
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$this->refreshCommand(); |
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if (!is_array($this->commandBuffer)) { |
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return ''; |
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} |
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switch($cmd = array_shift($this->commandBuffer)) { |
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case self::BYTE_SYS_MISSING: |
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return pack('d', -PHP_FLOAT_MAX); |
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case self::BYTE_SPACES: |
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return ' '; |
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case self::BYTE_LITERAL: |
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$result = $this->buffer->read(8); |
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if ($result === false) { |
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throw new \Exception('Stream read error'); |
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} |
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return $result; |
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case self::BYTE_NUL: |
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return $this->readBlock(); |
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throw new \Exception('0 byte command not supported'); |
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default: |
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// Bias |
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throw new \Exception('bias encoding not supported: ' . $cmd); |
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} |
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} |
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private function refreshCommand() |
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{ |
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if (empty($this->commandBuffer)) { |
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$this->commandBuffer = $this->buffer->readBytes(8); |
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} |
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} |
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public function read(int $length): string |
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{ |
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$result = substr($this->dataBuffer, 0, $length); |
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$length -= strlen($result); |
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while ($length > 0 && ($data = $this->readBlock()) !== '') |
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{ |
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if ($length >= strlen($data)) { |
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$result .= $data; |
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$length -= strlen($data); |
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} else { |
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$this->dataBuffer .= substr($data, $length); |
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return $result . substr($data, 0, $length); |
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} |
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} |
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1 |
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return $result; |
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} |
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} |
collecthor /
spss
This check looks for unreachable code. It uses sophisticated control flow analysis techniques to find statements which will never be executed.
Unreachable code is most often the result of
return,dieorexitstatements that have been added for debug purposes.In the above example, the last
return falsewill never be executed, because a return statement has already been met in every possible execution path.