How can you easily calculate the square root of an unsigned long long in C?
c, long-double, unsigned-long-long-int
Solution
Function `sqrtl()`, taking a `long double`, is part of C99.
Note that your compilation platform does not have to implement `long double` as 80-bit extended-precision. It is only required to be as wide as `double`, and Visual Studio implements is as a plain `double`. GCC and Clang do compile `long double` to 80-bit extended-precision on Intel processors.
Problem
I was looking at another question (here) where someone was looking for a way to get the square root of a 64 bit integer in x86 assembly. This turns out to be very simple. The solution is to convert to a floating point number, calculate the sqrt and then convert back. I need to do something very similar in C however when I look into equivalents I'm getting a little stuck. I can only find a sqrt function which takes in doubles. Doubles do not have the precision to store large 64bit integers without introducing significant rounding error. Is there a common math library that I can use which has a `long double` sqrt function?