We have hit a PHP mine!

Floating point numbers.

http://php.net/manual/en/language.types.float.php

When you compare two variables holding decimal values, NEVER trust the comparison operators. Basically, just use a mathematical function like round().

This is taken from PHP’s website:

Warning
Floating point precision

It is typical that simple decimal fractions like 0.1 or 0.7 cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9.

This is due to the fact that it is impossible to express some fractions in decimal notation with a finite number of digits. For instance, 1/3 in decimal form becomes 0.3.

So never trust floating number results to the last digit, and never compare floating point numbers for equality. If higher precision is necessary, the arbitrary precision math functions and gmp functions are available.”

So,

= $b){
  echo 'This may not work!?';
}
?>

..big disappointment 🙁

Leave a Reply