I would like to find out whether one real number is a multitude of the other one. I'm using BC-Math because the code is part of a larger system doing price calculations and using floats results in wrong results on multiple calculations due to the behaviour of floating point math.
BC-Math has bcmod() to get the modulus of an arbitrary precision number. However, before PHP 7.2 this function does not work with non-integer numeric strings. E.g:
echo bcmod('10', '9.2'); // 1, because '9.2' is truncated to '9'
Converting the numbers back to floats and using fmod() isn't an option since fmod function returning wrong result
I couldn't find any solution to this problem but I can't image that there is no solution.
EDIT:
Hello reader in the future who encounters the same problem! Based on @chiliNUT's response I created a pull-request for the bcmath-extended library.
I think it can be done using some math:
You can relate mod(a,b) to a and b with this equation:
a = b * floor(a/b) + mod(a,b)
and then solve that equation for mod to yield
mod(a,b) = a - b * floor(a/b)
Substituting your numbers you get
mod(10,9.2) = 10 - 9.2 * floor(10/9.2) = 0.8
Also see here for a bcmath floor implementation: How to ceil, floor and round bcmath numbers?