119 lines
3.3 KiB
PHP
119 lines
3.3 KiB
PHP
<?php
|
|
|
|
namespace IPLib\Service;
|
|
|
|
/**
|
|
* Helper class to work with unsigned binary integers.
|
|
*/
|
|
class BinaryMath
|
|
{
|
|
/**
|
|
* Trim the leading zeroes from a non-negative integer represented in binary form.
|
|
*
|
|
* @param string $value
|
|
*
|
|
* @return string
|
|
*/
|
|
public function reduce($value)
|
|
{
|
|
$value = ltrim($value, '0');
|
|
|
|
return $value === '' ? '0' : $value;
|
|
}
|
|
|
|
/**
|
|
* Compare two non-negative integers represented in binary form.
|
|
*
|
|
* @param string $a
|
|
* @param string $b
|
|
*
|
|
* @return int 1 if $a is greater than $b, -1 if $b is greater than $b, 0 if they are the same
|
|
*/
|
|
public function compare($a, $b)
|
|
{
|
|
list($a, $b) = $this->toSameLength($a, $b);
|
|
|
|
return $a < $b ? -1 : ($a > $b ? 1 : 0);
|
|
}
|
|
|
|
/**
|
|
* Add 1 to a non-negative integer represented in binary form.
|
|
*
|
|
* @param string $value
|
|
*
|
|
* @return string
|
|
*/
|
|
public function increment($value)
|
|
{
|
|
$lastZeroIndex = strrpos($value, '0');
|
|
if ($lastZeroIndex === false) {
|
|
return '1' . str_repeat('0', strlen($value));
|
|
}
|
|
|
|
return ltrim(substr($value, 0, $lastZeroIndex), '0') . '1' . str_repeat('0', strlen($value) - $lastZeroIndex - 1);
|
|
}
|
|
|
|
/**
|
|
* Calculate the bitwise AND of two non-negative integers represented in binary form.
|
|
*
|
|
* @param string $operand1
|
|
* @param string $operand2
|
|
*
|
|
* @return string
|
|
*/
|
|
public function andX($operand1, $operand2)
|
|
{
|
|
$operand1 = $this->reduce($operand1);
|
|
$operand2 = $this->reduce($operand2);
|
|
$numBits = min(strlen($operand1), strlen($operand2));
|
|
$operand1 = substr(str_pad($operand1, $numBits, '0', STR_PAD_LEFT), -$numBits);
|
|
$operand2 = substr(str_pad($operand2, $numBits, '0', STR_PAD_LEFT), -$numBits);
|
|
$result = '';
|
|
for ($index = 0; $index < $numBits; $index++) {
|
|
$result .= $operand1[$index] === '1' && $operand2[$index] === '1' ? '1' : '0';
|
|
}
|
|
|
|
return $this->reduce($result);
|
|
}
|
|
|
|
/**
|
|
* Calculate the bitwise OR of two non-negative integers represented in binary form.
|
|
*
|
|
* @param string $operand1
|
|
* @param string $operand2
|
|
*
|
|
* @return string
|
|
*/
|
|
public function orX($operand1, $operand2)
|
|
{
|
|
list($operand1, $operand2, $numBits) = $this->toSameLength($operand1, $operand2);
|
|
$result = '';
|
|
for ($index = 0; $index < $numBits; $index++) {
|
|
$result .= $operand1[$index] === '1' || $operand2[$index] === '1' ? '1' : '0';
|
|
}
|
|
|
|
return $result;
|
|
}
|
|
|
|
/**
|
|
* Zero-padding of two non-negative integers represented in binary form, so that they have the same length.
|
|
*
|
|
* @param string $num1
|
|
* @param string $num2
|
|
*
|
|
* @return string[],int[] The first array element is $num1 (padded), the first array element is $num2 (padded), the third array element is the number of bits
|
|
*/
|
|
private function toSameLength($num1, $num2)
|
|
{
|
|
$num1 = $this->reduce($num1);
|
|
$num2 = $this->reduce($num2);
|
|
$numBits = max(strlen($num1), strlen($num2));
|
|
|
|
return array(
|
|
str_pad($num1, $numBits, '0', STR_PAD_LEFT),
|
|
str_pad($num2, $numBits, '0', STR_PAD_LEFT),
|
|
$numBits,
|
|
);
|
|
}
|
|
}
|