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<?php
namespace Ds\Traits;
use Ds\Deque;
/**
* Common to structures that deal with an internal capacity. While none of the
* PHP implementations actually make use of a capacity, it's important to keep
* consistent with the extension.
*/
trait Capacity
{
/**
* @var int internal capacity
*/
private $capacity = self::MIN_CAPACITY;
/**
* Returns the current capacity.
*/
public function capacity(): int
{
return $this->capacity;
}
/**
* Ensures that enough memory is allocated for a specified capacity. This
* potentially reduces the number of reallocations as the size increases.
*
* @param int $capacity The number of values for which capacity should be
* allocated. Capacity will stay the same if this value
* is less than or equal to the current capacity.
*/
public function allocate(int $capacity)
{
$this->capacity = max($capacity, $this->capacity);
}
/**
* @return float the structures growth factor.
*/
protected function getGrowthFactor(): float
{
return 2;
}
/**
* @return float to multiply by when decreasing capacity.
*/
protected function getDecayFactor(): float
{
return 0.5;
}
/**
* @return float the ratio between size and capacity when capacity should be
* decreased.
*/
protected function getTruncateThreshold(): float
{
return 0.25;
}
/**
* Checks and adjusts capacity if required.
*/
protected function checkCapacity()
{
if ($this->shouldIncreaseCapacity()) {
$this->increaseCapacity();
} else {
if ($this->shouldDecreaseCapacity()) {
$this->decreaseCapacity();
}
}
}
/**
* @param int $total
*/
protected function ensureCapacity(int $total)
{
if ($total > $this->capacity()) {
$this->capacity = max($total, $this->nextCapacity());
}
}
/**
* @return bool whether capacity should be increased.
*/
protected function shouldIncreaseCapacity(): bool
{
return $this->count() >= $this->capacity();
}
protected function nextCapacity(): int
{
return (int) ($this->capacity() * $this->getGrowthFactor());
}
/**
* Called when capacity should be increased to accommodate new values.
*/
protected function increaseCapacity()
{
$this->capacity = max(
$this->count(),
$this->nextCapacity()
);
}
/**
* Called when capacity should be decrease if it drops below a threshold.
*/
protected function decreaseCapacity()
{
$this->capacity = max(
self::MIN_CAPACITY,
(int) ($this->capacity() * $this->getDecayFactor())
);
}
/**
* @return bool whether capacity should be increased.
*/
protected function shouldDecreaseCapacity(): bool
{
return count($this) <= $this->capacity() * $this->getTruncateThreshold();
}
}
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