bit wise operator in PHP and JS, USAGE in DB

 

https://www.php.net/manual/en/language.operators.bitwise.php

https://www.w3schools.com/js/js_bitwise.asp

$a & $b	And	Bits that are set in both $a and $b are set.
$a | $b	Or (inclusive or)	Bits that are set in either $a or $b are set.
$a ^ $b	Xor (exclusive or)	Bits that are set in $a or $b but not both are set.
~ $a	Not	Bits that are set in $a are not set, and vice versa.
$a << $b	Shift left	Shift the bits of $a $b steps to the left (each step means "multiply by two")
$a >> $b	Shift right	Shift the bits of $a $b steps to the right (each step means "divide by two")

5 >> 1, move 1 over to left bit (divide by 2)

5 >> 2, move 2 over to left bit(dived by 4)

Operation Result Same as Result 5 & 1 1 0101 & 0001  0001 5 | 1 5 0101 | 0001  0101 ~ 5 10  ~0101  1010 5 << 1 10 0101 << 1  1010 5 ^ 1 4 0101 ^ 0001  0100 5 >> 1 2 0101 >> 1  0010 5 >>> 1 2 0101 >>> 1  0010

<?php

// PHP program to Count set

// bits in an integer

 

// Function to get no of set 

// bits in binary representation

// of positive integer n

function countSetBits($n)

{

    $count = 0;

    while ($n)

    {

        $count += $n & 1;

        $n >>= 1;

    }

    return $count;

}

 

// Driver Code

$i = 9;

echo countSetBits($i);

 

// This code is contributed by ajit

?>




https://www.geeksforgeeks.org/count-set-bits-in-an-integer/







x >>= 1 means "set x to itself shifted by one bit to the right". The expression evaluates to the new value of x after the shift. (x = x >> 1;)




https://stackoverflow.com/questions/38922606/what-is-x-1-and-x-1




x+=1 is more effiecent that x=x+1, as x+=1 only evaludated once




https://stackoverflow.com/questions/808062/x-x1-vs-x-1







Usage in DB

Instead of creating multiple columns in DB for flag values, just create one column called "bit" with the addition of flag values :

'bits' => array(

'flag1' => 1,

'flag2' => 2,

'flag3' => 4,

'flag4' => 8,

),

If flag1, flag2, flag3, flag4 are all turned on, just save total sum of 15 into "bits" column

and to check which flag is turned on, do bitwise operation &,

15 & flag 1 (1), should be 1(shared bit is 01), 15 & flag 2 (2) should be 2(shared bit is 10).

If not turned on & operation gives 0,