Php precision with floating point - complex equation = 1

I have the following equation

1 - ((.5 * 0.83333333333333) ^ 2 + (.5 * 0.83333333333333) ^ 2 + (.5 * (1 - 0.83333333333333)) ^ 2 + (.5 * (1 - 0.83333333333333)) ^ 2)

In Php5, this results in an answer of 1 as opposed to .63 (on two machines, OSx and Centos). Should I be exclusively using the bc math functions of Php to do equations like this?

From stackoverflow

• I think maybe you should be using pow() instead of the xor operator (^) :)

• Shoot me now. Please. :)

  Thanks!

• Not really an equation, but thats semantics. also, I doubt you mean xor, so I'll assume that isn't what you want. Anyway, can you use rational arithmetic?

  0.83333 can be converted to a fraction (assuming the 3 is a repeating decimal):

   83.3333333 = 100x
    8.3333333 = 10x
   -----------------
           75 = 90x
       x = 75 / 90 = 0.83333...
  

  That way you are dealing with integers only, and as long as both don't overflow (you can reduce by GCD prior to and after operations) then you should be fine.

• <?php
  
  $hugeDamnEquation = pow(1 - ((.5 * 0.83333333333333), 2) + pow((.5 * 0.83333333333333), 2) + pow((.5 * (1 - 0.83333333333333)), 2) + pow((.5 * (1 - 0.83333333333333)), 2));
  
  echo $hugeDamnEquation;
  
  ?>