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<?php |
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declare(strict_types=1); |
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namespace Ivory\Value; |
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/** |
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* Fixed-length bit string - a string of 1's and 0's. |
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* |
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* The objects are immutable, i.e., operations always produce a new object. |
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* The representation and operations resemble the specification of the `BIT` type in PostgreSQL. |
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* |
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* It is possible to access individual bits using the array indices (readonly). The leftmost bit is at offset 0. Testing |
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* whether the bit string has a bit at a given offset may be performed using `isset($this[$offset])`. Note that, apart |
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* from reading out of such a call, it does not test whether the given bit is *set* (i.e., whether it is 1) - it merely |
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* tests whether it is legal to access it. Negative offsets may be used to get bits off the end of the string. |
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* |
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* @see http://www.postgresql.org/docs/current/static/datatype-bit.html PostgreSQL Bit String Types |
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* @see http://www.postgresql.org/docs/current/static/functions-bitstring.html PostgreSQL Bit String Functions and Operators |
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*/ |
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class FixedBitString extends BitString |
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{ |
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/** |
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* @param string $bits the bit string, i.e., a string of 1's and 0's |
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* @param int|null $length length of the bit string in bits; |
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* <tt>null</tt> for taking the length of <tt>$bits</tt>; |
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* if less or greater than <tt>strlen($bits)</tt>, the bits get zero-padded or truncated on |
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* the right to be exactly <tt>$length</tt> bits (and a warning is issued is case of |
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* truncation) |
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* @return FixedBitString |
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* @throws \InvalidArgumentException if <tt>$length</tt> is a non-positive number (PostgreSQL forbids it) |
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*/ |
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public static function fromString(string $bits, ?int $length = null): FixedBitString |
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{ |
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$bits = (string)$bits; |
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$bitsLen = strlen($bits); |
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if ($length === null) { |
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return new FixedBitString($bits); |
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} elseif ($length <= 0) { |
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throw new \InvalidArgumentException('length is non-positive'); |
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} elseif ($length == $bitsLen) { |
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return new FixedBitString($bits); |
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} elseif ($length > $bitsLen) { |
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return new FixedBitString(str_pad($bits, $length, '0')); |
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} else { // $length < $bitsLen |
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trigger_error("Bit string truncated to the length of $length", E_USER_WARNING); |
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return new FixedBitString(substr($bits, 0, $length)); |
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} |
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} |
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/** |
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* Creates a bit string as the two's complement of a given integer represented on a given number of bits. |
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* |
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* The least significant bit is the rightmost one in the resulting bit string. |
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* |
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* Overflows are not detected - if `$length` is not sufficient for representing the whole `$int`, only the `$length` |
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* least significant bits of the representation are used quietly, without any notice. |
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* |
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* @param int $int integer to represent |
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* @param int $length number of bits |
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* @return FixedBitString |
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* @throws \InvalidArgumentException if <tt>$length</tt> is a non-positive number |
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*/ |
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public static function fromInt(int $int, int $length): FixedBitString |
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{ |
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if ($length <= 0) { |
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throw new \InvalidArgumentException('length <= 0'); |
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} |
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$bin = decbin($int); |
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$padBit = ($int >= 0 ? '0' : '1'); |
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$padded = str_pad($bin, $length, $padBit, STR_PAD_LEFT); |
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$truncated = substr($padded, -$length); |
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return self::fromString($truncated); |
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} |
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/** |
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* Returns a non-negative integer encoded by the bits in the bit string. |
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* |
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* The standard binary encoding is used. The rightmost bit in the string is the least significant in the integer. |
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* |
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* Only that many rightmost bits are taken which allow the encoded integer be represented correctly by the PHP `int` |
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* type. That is 31 bits or 63 bits depending on whether this is a 32-bit or 64-bit compilation of PHP. |
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* |
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* For getting an arbitrary-length integer instead of the truncated `int`, use {@link toNumber()}. |
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* |
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* Note that, unlike {@link fromInt()}, this method does NOT work with the two's complement, but rather with the |
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* standard binary encoding, and thus never returns any negative number. This is to resemble the PostgreSQL |
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* behaviour. |
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* |
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* @return int |
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*/ |
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public function toInt(): int |
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{ |
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return bindec(substr($this->bits, -(PHP_INT_SIZE * 8 - 1))); |
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} |
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} |
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ondrej-bouda /
ivory
