For arbitrary precision mathematics PHP offers the Binary Calculator (BCMATH library of functions) which supports numbers of any size and precision, represented as strings.

The BCMATH library includes the following functions:

bcadd() - Add two arbitrary precision numbers

bccomp() - Compare two arbitrary precision numbers

bcdiv() - Divide two arbitrary precision numbers

bcmod() - Get modulus of an arbitrary precision number

bcmul() - Multiply two arbitrary precision number

bcpow() - Raise an arbitrary precision number to another

bcpowmod() - Raise an arbitrary precision number to another, reduced by a specified modulus

bcscale() - Set
default scale parameter for all bc math functions

bcsqrt() - Get the square root of an arbitrary precision number

bcsub() - Subtract one arbitrary precision number
from another

This test uses 8 of the 10 (all but bcpowmod() and bcscale()) predefined functions included in the BCMATH library. This test is successful when a (correct)
result is displayed in the red box(es) for each of the functions.