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<?php |
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namespace ASN1\Util; |
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use ASN1\Type\Primitive\BitString; |
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/** |
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* Class to handle a bit string as a field of flags. |
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*/ |
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class Flags |
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{ |
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/** |
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* Flag octets. |
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* |
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* @var string $_flags |
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*/ |
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protected $_flags; |
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/** |
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* Number of flags. |
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* |
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* @var int $_width |
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*/ |
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protected $_width; |
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/** |
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* Constructor |
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* |
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* @param number $flags Flags |
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* @param int $width The number of flags. If width is larger than number of |
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* bits in $flags, zeroes are prepended to flag field. |
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*/ |
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public function __construct($flags, $width) { |
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if (!$width) { |
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$this->_flags = ""; |
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} else { |
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// calculate number of unused bits in last octet |
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$last_octet_bits = $width % 8; |
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$unused_bits = $last_octet_bits ? 8 - $last_octet_bits : 0; |
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$num = gmp_init($flags); |
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// mask bits outside bitfield width |
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$mask = gmp_sub(gmp_init(1) << $width, 1); |
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$num &= $mask; |
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// shift towards MSB if needed |
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$data = gmp_export($num << $unused_bits, 1, |
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GMP_MSW_FIRST | GMP_BIG_ENDIAN); |
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$octets = unpack("C*", $data); |
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$bits = count($octets) * 8; |
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// pad with zeroes |
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while ($bits < $width) { |
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array_unshift($octets, 0); |
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$bits += 8; |
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} |
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$this->_flags = pack("C*", ...$octets); |
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} |
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$this->_width = $width; |
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} |
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/** |
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* Initialize from BitString. |
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* |
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* @param BitString $bs |
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* @param int $width |
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* @return self |
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*/ |
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public static function fromBitString(BitString $bs, $width) { |
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$num_bits = $bs->numBits(); |
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$num = gmp_import($bs->string(), 1, GMP_MSW_FIRST | GMP_BIG_ENDIAN); |
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$num >>= $bs->unusedBits(); |
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if ($num_bits < $width) { |
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$num <<= ($width - $num_bits); |
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} |
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return new self(gmp_strval($num, 10), $width); |
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} |
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/** |
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* Check whether a bit at given index is set. |
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* Index 0 is the leftmost bit. |
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* |
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* @param int $idx |
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* @throws \OutOfBoundsException |
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* @return bool |
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*/ |
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public function test($idx) { |
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if ($idx >= $this->_width) { |
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throw new \OutOfBoundsException("Index is out of bounds."); |
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} |
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// octet index |
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$oi = (int) floor($idx / 8); |
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$byte = $this->_flags[$oi]; |
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// bit index |
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$bi = $idx % 8; |
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// index 0 is the most significant bit in byte |
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$mask = 0x01 << (7 - $bi); |
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return (ord($byte) & $mask) > 0; |
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} |
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/** |
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* Get flags as an octet string. |
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* Zeroes are appended to the last octet if width is not divisible by 8. |
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* |
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* @return string |
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*/ |
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public function string() { |
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return $this->_flags; |
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} |
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/** |
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* Get flags as a base 10 integer. |
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* |
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* @return int|string |
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*/ |
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public function number() { |
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$num = gmp_import($this->_flags, 1, GMP_MSW_FIRST | GMP_BIG_ENDIAN); |
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$last_octet_bits = $this->_width % 8; |
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$unused_bits = $last_octet_bits ? 8 - $last_octet_bits : 0; |
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$num >>= $unused_bits; |
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return gmp_strval($num, 10); |
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} |
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/** |
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* Get flags as a BitString. |
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* Unused bits are set accordingly. Trailing zeroes are not stripped. |
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* |
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* @return BitString |
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*/ |
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public function bitString() { |
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$last_octet_bits = $this->_width % 8; |
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$unused_bits = $last_octet_bits ? 8 - $last_octet_bits : 0; |
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return new BitString($this->_flags, $unused_bits); |
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} |
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} |
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sop /
asn1
