Question

How to get the lowest order set bit of a number in PHP

Answer 1

define('INT_SIZE', PHP_INT_SIZE * 8);

function getLowestOrderSetBit($number) {
    $lowestOrderBitIndex = -1;
    
    for ($i = 0; $i < INT_SIZE; $i++) {
        if (($number >> $i) & 1 == 1) {
            $lowestOrderBitIndex = $i;
            break;
        }
    }
    
    return $lowestOrderBitIndex;
}

$number = 1688; // 11010011000

$lowestOrderBitIndex = getLowestOrderSetBit($number);

echo $lowestOrderBitIndex;


    
    
/*
run:
   
3
    
*/

 

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