CODEWITHSUNDEEP
phpbit-manipulationbitmaskcomparison-operators
hakuna matata
hakuna matata

Reputation: 3327

PHP bitwise operations not returning correct values

I have a function which takes a numbers and returns an array corresponding to the days (the number will be bit-masked for each day of the week). However the array is returning all the days for certain values and an empty array for another values. Below is the function 

function get_days($days) {
    $days_arr = array();


echo "days: " . decbin($days) . " - type: " . gettype($days) . "<br/>";
echo "type1: " . gettype($days & 0x01) . " - type2: " . gettype(0x01) . "<br/>";
echo "days & 0x01 = " . dechex($days & 0x01) . " = " . ($days & 0x01 == 0x01) . "<br/>";
echo "days & 0x02 = " . dechex($days & 0x02) . " = " . ($days & 0x02 == 0x02) . "<br/>";
echo "days & 0x04 = " . dechex($days & 0x04) . " = " . ($days & 0x04 == 0x04) . "<br/>";
echo "days & 0x08 = " . dechex($days & 0x08) . " = " . ($days & 0x08 == 0x08) . "<br/>";
echo "days & 0x10 = " . dechex($days & 0x10) . " = " . ($days & 0x10 == 0x10) . "<br/>";


    if($days & 0x01 == 0x01)
        $days_arr[] = 'M';

    if($days & 0x02 == 0x02)
        $days_arr[] = 'T';

    if($days & 0x04 == 0x04)
        $days_arr[] = 'W';

    if($days & 0x08 == 0x08)
        $days_arr[] = 'H';

    if($days & 0x10 == 0x10)
        $days_arr[] = 'F';

    return $days_arr;
}

Below are the results of the echo 

days: 10101 - type: integer
type1: integer - type2: integer
days & 0x01 = 1 = 1
days & 0x02 = 0 = 1
days & 0x04 = 4 = 1
days & 0x08 = 0 = 1
days & 0x10 = 10 = 1
days: 1010 - type: integer
type1: integer - type2: integer
days & 0x01 = 0 = 0
days & 0x02 = 2 = 0
days & 0x04 = 0 = 0
days & 0x08 = 8 = 0
days & 0x10 = 0 = 0

I can't seem to figure the reason behind the issue, it seems logical to me that this should work.

Upvotes: 2

Views: 173

Answers (1)

KIKO Software
KIKO Software

Reputation: 16688

This is an operator precedence issue. See:

http://php.net/manual/en/language.operators.precedence.php

So == is above &. You should not do:

$days & 0x02 == 0x02

But:

($days & 0x02) == 0x02

Upvotes: 1

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