Mathematical Function For Each Binary Bit

[Vel]

I'm going through a loop and using an AND check to see if an appropriate flag has been set, and if so increase the appropriate hour by 1. Code is (without all the SQL getting the data):

<?php
while($row = $result->fetch_row()) {
for($j = 0; $j < $bat->length; $j++) {
 $bwt = $bitwise_array[$j];
 if(($row[0] & $bwt) == $bwt)
  $hours[$j]++;
}
}

Right now bitwise array is just a manually populated array with 1,2,4,8,16 etc... However is there a mathematical function for calculating the proper bit in decimal?

[Pikachu2000]

What do you mean by "calculating the proper bit"?

[Vel]

So in binary the first bit = 1, the second bit = 2, the third bit = 4, the fourth = 8 and so on. I have manually filled in an array for that. If I specify the bit, is there a function that will give me the decimal value of that bit. I always thought it was 2n, but that does't work.

[Pikachu2000]

It still isn't completely clear, but if you have the binary string '01000', you can use bindec to get the decimal value. If that isn't what you mean, post an example of the actual data, and the expected output.

[Vel]

OK, in the code above the function goes from 0 up to an unknown number (max of 11). Each loop through it tests the result row[0] for the next bit to see if it is set. So first loop through it is

if(($row[0] & 1) == 1)
$hours[$j]++;

 

Second loop through it's

 

if(($row[0] & 2) == 2)
$hours[$j]++;

 

Third...

if(($row[0] & 4) == 4)
$hours[$j]++;

 

If you see my OP that number is a variable, $bwt. That is determined by a manually filled in array right now. However what I want is a mathematical function to get that number for me, so I can put in the bit, and get the decimal value for it: i.e.

Bit = Decimal

1 = 1

2 = 2

3 = 4

4 = 8

5 = 16

6 = 32

7 = 64

8 = 128

and so on.

Edited October 28, 2012 by Vel

[Pikachu2000]

So something like this, then?

 

for( $i = 0; $i < 12; $i++ ) {
echo "Bit position: $i - Bit value: " . pow(2, $i) . '<br>';
}

[Vel]

Yes, that's exactly what I was after. Thank you very much. Never heard of the pow function before.

Edited October 28, 2012 by Vel

[kicken]

Note you can just use the bitshift operators too.

 

echo (1<<0) . PHP_EOL; //1
echo (1<<1) . PHP_EOL; //2
echo (1<<2) . PHP_EOL; //4
echo (1<<3) . PHP_EOL; //8
echo (1<<4) . PHP_EOL; //16
//...

 

The expression y<<x moves the bits in y x places to the left.  When y is 1 (pattern 00000001) then you're just moving the one bit x place.  eg 1<<5 would be (00100000)

[silkfire]

Use the pow() function for powers: 2³ = pow(2, 3) = 8