Check if two numbers have same bits set

Question

I have two decimal numbers. If both the bits at any identical positions are set, then comparison should return true otherwise false. For example

number1 = 196 = 11000100
number2 = 4 = 00000100
number3 = 16 = 00010000

=> Comparison of number1 and number2 will return true.

=> Comparison of number1 and number3 will return false.

=> Comparison of number2 and number3 will return false.

In PHP, is there any inbuilt function for this type of comparison or how can we write custom logic for it?

https://www.php.net/manual/en/language.operators.bitwise.php — AbraCadaver, Jan 08 '20 at 12:21
Pretty unclear question indeed. You need to explain the steps as well as how do you derive something as `true` or `false`! You just need the check of `($a & $b) != 0` — nice_dev, Jan 08 '20 at 12:40
@JohnPancoast's answer at the duplicate is pretty informative. — mickmackusa, Jan 08 '20 at 13:03

score 3 · Accepted Answer · answered Jan 08 '20 at 12:31

From Bitwise Operators:

$a & $b And Bits that are set in both $a and $b are set.

var_dump(196 & 4);
var_dump(196 & 16);
var_dump(4 & 16);

Where 0 is false non-zero is true:

int(4)
int(0)
int(0)

You can cast to boolean true or false:

var_dump((bool) (196 & 4));

score 0 · Answer 2 · answered Jan 08 '20 at 12:32

0

Use bitwise operators:

$number1 = 196;
$number2 = 4;

if ($number1 & $number2){
  echo "Number 1 and 2 are equal";
} else {
  echo "Number 1 and 2 are not equal";
}

answered Jan 08 '20 at 12:32

mrzo

2,002
1
14
26

score 0 · Answer 3 · answered Jan 08 '20 at 12:34

The bitwise answer is way better than mine, but here's how to do it without using bitwise operators:

<?php


function hasMatchingBits($x, $y) 
{
    $x = strrev(decbin($x));
    $y = strrev(decbin($y));
    $lengthX = strlen($x);
    $lengthY = strlen($y);
    $length = $lengthX < $lengthY ? $lengthX : $lengthY;

    for ($i = 0; $i < $length; $i++) {
        if ($x[$i] === '1' && $y[$i] === '1') {
            return true;
        }
    }

    return false;
}

echo hasMatchingBits(196, 4) ? "Yes\n" : "No\n";
echo hasMatchingBits(196, 16) ? "Yes\n" : "No\n";
echo hasMatchingBits(4, 16) ? "Yes\n" : "No\n";

Which you can see here https://3v4l.org/8lSJX

This was exactly what I have used earlier – Dinesh Belkare Jan 14 '20 at 09:50 — Dinesh Belkare, Jan 14 '20 at 09:50

Check if two numbers have same bits set

3 Answers3