When floor-ing a result of a multiplication I get a different result than when floor-ing a normal number. Is this behaviour expected? If yes, why?
$val1 = 29;
$val2 = 0.29*100;
echo floor($val1); // prints 29
echo floor($val2); // prints 28
This is a result of floating point precision in PHP, in your example:
gettype($val1); returns integer
and
gettype($val2); returns double
Combine that with this warning on php.net:
Additionally, rational numbers that are exactly representable as floating point numbers in base 10, like 0.1 or 0.7, do not have an exact representation as floating point numbers in base 2, which is used internally, no matter the size of the mantissa. Hence, they 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 7.9999999999999991118....
taken from http://php.net/manual/en/language.types.float.php
And we can see why your floor takes it from 28.9999999999 etc down to 28, instead of the integer 29 to 29.