When should I use a bitwise operator?

Question

I read the following Stack Overflow questions, and I understand the differences between bitwise and logical.

• Difference between & and && in

Answer 1

Well, asuming there is $x = (false && some_function());, here the value of $x will be set without calling the some_function() because the first value was FALSE.

But what if you needed to call that function anyway? Use $x = (false & some_function());.

In other words, the & uses MORE processing than the &&, just because && does not run through all the values to check them. If it found one value as false, it would return it, not looking at other values.

And in logical operations, use the && operator as it's used to return the logical operation value, where & is used to set a value and in an if statement it will always return true.

Answer 2

In most cases, you'll probably want to use logical operators. They're used for combining logical conditions, generally to control program flow, e.g. ($isAlive && $wantsToEat).

Bitwise operators are used when you want to perform operations on a bit-by-bit basis on the underlying binary representations of integers. e.g. (5 & 3) == 7. As others have suggested, there's usually not a lot of call for this in the sort of application that tends to get written in PHP (although there is in lower-level languages, like C).

Answer 3

Bitwise is useful for things in PHP just like anything else.

How about a value that can have multiple states turned on at the same time?

<?php

// since we're setting constant values in base10 we must progressively double
// them since bitwise operations work in base2. you'll see why when we output
// these as binary values below.
const STATE_FOO = 1;
const STATE_BAR = 2;
const STATE_FEZ = 4;
const STATE_BAZ = 8;

// show base2 values of the above constants
echo sprintf("STATE_FOO's base2 value is %08d\n", decbin(STATE_FOO));
echo sprintf("STATE_BAR's base2 value is %08d\n", decbin(STATE_BAR));
echo sprintf("STATE_FEZ's base2 value is %08d\n", decbin(STATE_FEZ));
echo sprintf("STATE_BAZ's base2 value is %08d\n\n", decbin(STATE_BAZ));

// set state to FOO and FEZ
$state = STATE_FOO | STATE_FEZ;

echo sprintf("base10 value of \$state is %s\n", $state);
echo sprintf("base2 value of \$state is %08d\n", decbin($state));
echo sprintf("Does \$state include FOO state? %s\n", (bool)($state & STATE_FOO));
echo sprintf("Does \$state include BAR state? %s\n", (bool)($state & STATE_BAR));
echo sprintf("Does \$state include FEZ state? %s\n", (bool)($state & STATE_FEZ));
echo sprintf("Does \$state include BAZ state? %s\n", (bool)($state & STATE_BAZ));
echo sprintf("Is state equivalent to FOO and FEZ states? %s\n", ($state == (STATE_FOO | STATE_FEZ)));

Output:

STATE_FOO's base2 value is 00000001
STATE_BAR's base2 value is 00000010
STATE_FEZ's base2 value is 00000100
STATE_BAZ's base2 value is 00001000

base10 value of $state is 5
base2 value of $state is 00000101
Does $state include FOO state? 1
Does $state include BAR state?
Does $state include FEZ state? 1
Does $state include BAZ state?
Is state equivalent to FOO and FEZ states? 1