Question

I use the code below to calculate log base 2.

Math.log(x)/Math.log(2);

With this function, i get nan if x=4/5.

With calc, excel this problem don’t exist.

How to avoid to get nan and get the real value?

Answer 1

I have a strong feeling that your 4/5 is integers. Which would mean that 4/5 will evaluate to 0 due to integer division.

log(0) is negative infinity, that could be the source of your NaN.

To fix this, cast your numbers to floating-point before you do the division:

double x = (double)4 / 5;