Bitwise Compressed Booleans - Toggling Specific Ones - php

Question

Background
I have to store a number of true/false values in a database, and rather than make many columns, I instead am using a single int column, where I store all of the booleans, compressed using Bitwise operators.
Example:
Product 1 is certified as:
Lead Free - Yes
Gluton Free - No
Free Range - Yes
Organic - Yes
So in the DB, in the certs column, I'd compress 1, 0, 1, 1 into 13 (1 + 4 + 8).
I've written quick wrapper functions to compress and extract this information (change from int into boolean array and back).
Problem
I'm not sure of the best way to quickly add and remove values from this. Say I want to update the product to NOT be Free Range anymore. I can take the compressed int, minus 4. That works. Except what if it already wasn't Free Range? If I'm doing bulk operations, I need my function to only remove 4 from products that are currently certified Free Range, or the number gets messed up.
I have figured it out with a lengthy if statement, but it's not elegant. This works:
// $certs_current is the compressed int from the DB.
// $certs_new is a new integer. 4 would mean toggle "Free Range" to true. -4 would mean toggle it to false.
if ( $certs_current & abs($certs_new) ) {
if ( $certs_new < 0 ) {
$certs_current += $certs_new;
}
} else {
if ( $certs_new > 0 ) {
$certs_current += $certs_new;
}
}
This is a lot of if statements. I played around with the | operator, but it only works for adding positive numbers. Pass it a -4 and it breaks. And I can't figure out a nor operator.
Is there a better way to do this?
Edit:
In other words, is there an operator where: If I give it 13 and -4, it'll give me 9. But if I give it 9 and -4, it'll give 9? Or even just 13 and 4.
Edit 2
Adding in the | to my working logic, I've reduced the complexity and still have it working:
if ( $certs_new > 0 ) {
$certs_current = ( $certs_current | $certs_new );
} else {
if ( $certs_current & abs($certs_new) ) {
$certs_current += $certs_new;
}
}
Basically it says, if the new number is positive, then use the | operator to add it if it needs to be added. If it's negative, then we first check to see if we need to remove it, and if so, remove it. Which is the place where I think we can improve.
The | replaces an if statement, because it only adds the 4 if the 4 isn't already toggled to true (I realized that's a weird way to describe it).
But with the negative number, I still have a nested if statement, which is what I want to remove if possible.

Answer 1

You have the compressed value, so why don't you expand it before doing your operations?
$certs_temp = $certs_current
$is_organic = $certs_temp >= 8 && $certs_temp -= 8
$is_freerange = $certs_temp >= 4 && $certs_temp -= 4
$is_glutenfree = $certs_temp >= 2 && $certs_temp -= 2
$is_leadfree = $certs_temp >= 1 && $certs_temp -= 1
And then re-compress with the changed values (if indeed anything has changed).
I think you are asking for trouble if you try to operate directly on the stored integer, which actually represents 4 separate binary flags. Either represent each flag separately in the DB, or if you must have it stored as an integer, then decode it before applying changes or logic.

Answer 2

Answer
I figured it out. To toggle a boolean to false, we need to:
Reverse the primary compressed int from the DB, using ~ (13 in the example)
Add in the absolute value of the new int 4 ( not -4), using |.
Re-reverse the full int again, using ~.
So the final code, with only one if statement:
if ( $certs_new > 0 ) {
$certs = ( $certs | $certs_new );
} else {
$certs = ~( ~$certs | abs($certs_new) );
}
// 13 and 4 .... 13
// 13 and 2 .... 15
// 13 and -4 .... 9
// 13 and -2 .... 13