用位圖BitMap節省空間

某一個字段用於存儲商品的id和商品分類id，假設分類id小於等於255，商品id小於等65535，如果用int存儲，在32位機器上至少要64位，而採用位圖則只需要32位即可。

class Bits
{
    protected $bits = 0;

    function setGoodId($goodId)
    {
        $this->bits += $goodId << 8;
    }
    
    function setCateId($cateId)
    {
        $this->bits += $cateId;
    }
    
    function getCateId()
    {
        return $this->bits & 255;
    }
    
    function getGoodId()
    {
        return $this->bits  >> 8;
    }

    function show()
    {
        return $this->bits;
    }
}

$cateId = 234; //分類id小於等於255（2的8次方）
$goodId = 12345; //商品id小於等於65535(2的16次方)
$obj = new Bits();
$obj->setCateId($cateId);
$obj->setGoodId($goodId);
echo $obj->getGoodId() . "\n";
echo $obj->getCateId() . "\n";
echo $obj->show();

[Running] php "/Users/why/Desktop/php/why.php"
12345
234
3160554