Question

How to set specific bits and find the set bits indexes in PHP

Answer 1

define('BIT_SIZE', 16);

// Function to print binary representation of the bits
function printBinary(int $bits): void {
    for ($i = BIT_SIZE - 1; $i >= 0; $i--) {
        echo ($bits >> $i) & 1;
    }
    echo PHP_EOL;
}

function findFirstSetBit(int $bits): int {
    for ($i = 0; $i < BIT_SIZE; $i++) {
        if (($bits >> $i) & 1) {
            return $i;
        }
    }
    return -1; // No bits set
}

function printSetBitIndexes(int $bits): void {
    for ($i = 0; $i < BIT_SIZE; $i++) {
        if (($bits >> $i) & 1) {
            echo $i . ' ';
        }
    }
    echo PHP_EOL;
}

$bits = 0;
$bits |= (1 << 3);
$bits |= (1 << 5);
$bits |= (1 << 11);
$bits |= (1 << 14);

printBinary($bits);

echo "First set bit at index: " . findFirstSetBit($bits) . PHP_EOL;

echo "All the set bits indexes:" . PHP_EOL;
printSetBitIndexes($bits);

  
  
/*
run:
    
0100100000101000
First set bit at index: 3
All the set bits indexes:
3 5 11 14 

*/

 

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