如何获得一个非常大的数字（PHP）的log（）？

Question

I've looked at php-big numbers, BC Math, and GMP for dealing with very big numbers in php. But none seem to have a function equivilent to php's log(). For example I want to do this:

$result = log($bigNumber, 2);

Would anyone know of an alternate way to get the log base 2 of a arbitray precision point number in php? Maybe Ive missed a function, or library, or formula.

edit: php-bignumbers seems to have a log base 10 function only log10()

Answer 1

One solution combining the suggestions so far would be to use this formula:

log2($num) = log10($num) / log10(2)

in conjunction with php-big numbers since it has a pre-made log10 function.

eg, after installing the php-big numbers library, use:

$log2 = log10($bigNum) / log10(2);

Personally I've decided to use different math/logic so as to not need the log function, and just using bcmath for the big numbers.