Reverting a bitwise/binary number to an array of values? - php

Question

I have a a list of data that has a value attached to it that constantly gets doubled as it goes up:
0 = value 0
1 = value 1
2 = value 2
4 = value 3
8 = value 4
16 = value 5
32 = value 6
64 = value 7
128 = value 8
256 = value 9
512 = value 10
I have also been given the number x
say x = 76.
Visually, I can see that value 7 (64), value 4 (8), and value 3 (4) all sum up to 76.
What I need to be able to do, is take x, run it through a function, and return an array of the values.
I've tried looping through all the numbers in reverse and taking off what value has been used, but i got confused with lots of if statements.
Is there a built in PHP function to do this? Or am I looking at it the wrong way?
Thanks

Answer 1

May be you are looking for this-
function getArray($x){
$ar = array();
for($i = 0 ; $i < 16; $i++){
if( ($x&(1<<$i)) != 0 ){
array_push($ar, (1<<$i));
// if you need positions; you should use it instead of above line
//array_push($ar, ($i+1));
}
}
return $ar;
}
print_r( getArray(76) );
Output:
Array (
[0] => 4
[1] => 8
[2] => 64
)
The alternate output will be (if you use array_push($ar, ($i+1));)-
Array
(
[0] => 3
[1] => 4
[2] => 7
)
Explanation:
In binary 76 presents 00000000 01001100 in 16 bit. I ran a loop from Least Significant Bit (LSB) to Most Significant Bit (MSB) (0-16). In each loop, I'm generating a new number which contains only i'th bit as 1 and rest of the bits are 0. To generate it I used shifting operator (1 << i) which is actually 2^i. Now I did a bit wise AND operation between x and the new number. If this operation returns any nonzero number that means i'th bit of x is 1 and I'm pushing that position/value inside the array. Finally I'm returning that arry.