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<?php
/*
* This file is part of the PHPASN1 library.
*
* Copyright © Friedrich Große <friedrich.grosse@gmail.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace FG\ASN1\Universal;
use Exception;
use FG\ASN1\Exception\ParserException;
use FG\ASN1\Parsable;
use FG\ASN1\Identifier;
class BitString extends OctetString implements Parsable
{
private $nrOfUnusedBits;
/**
* Creates a new ASN.1 BitString object.
*
* @param string|int $value Either the hexadecimal value as a string (spaces are allowed - leading 0x is optional) or a numeric value
* @param int $nrOfUnusedBits the number of unused bits in the last octet [optional].
*
* @throws Exception if the second parameter is no positive numeric value
*/
public function __construct($value, $nrOfUnusedBits = 0)
{
parent::__construct($value);
if (!is_numeric($nrOfUnusedBits) || $nrOfUnusedBits < 0) {
throw new Exception('BitString: second parameter needs to be a positive number (or zero)!');
}
$this->nrOfUnusedBits = $nrOfUnusedBits;
}
public function getType()
{
return Identifier::BITSTRING;
}
protected function calculateContentLength()
{
// add one to the length for the first octet which encodes the number of unused bits in the last octet
return parent::calculateContentLength() + 1;
}
protected function getEncodedValue()
{
// the first octet determines the number of unused bits
$nrOfUnusedBitsOctet = chr($this->nrOfUnusedBits);
$actualContent = parent::getEncodedValue();
return $nrOfUnusedBitsOctet.$actualContent;
}
public function getNumberOfUnusedBits()
{
return $this->nrOfUnusedBits;
}
public static function fromBinary(&$binaryData, &$offsetIndex = 0)
{
self::parseIdentifier($binaryData[$offsetIndex], Identifier::BITSTRING, $offsetIndex++);
$contentLength = self::parseContentLength($binaryData, $offsetIndex, 2);
$nrOfUnusedBits = ord($binaryData[$offsetIndex]);
$value = substr($binaryData, $offsetIndex + 1, $contentLength - 1);
if ($nrOfUnusedBits > 7 || // no less than 1 used, otherwise non-minimal
($contentLength - 1) == 1 && $nrOfUnusedBits > 0 || // content length only 1, no
(ord($value[strlen($value)-1])&((1<<$nrOfUnusedBits)-1)) != 0 // unused bits set
) {
throw new ParserException("Can not parse bit string with invalid padding", $offsetIndex);
}
$offsetIndex += $contentLength;
$parsedObject = new self(bin2hex($value), $nrOfUnusedBits);
$parsedObject->setContentLength($contentLength);
return $parsedObject;
}
}
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