Just recently, the GCC 4.6.0 came out along with libquadmath. Unfortunately, GNU has supported Fortran, but not C or C++ (all that is included is a .so). I have not found a way to use these new features in C++, however, GNU C does support the __float128 type for guaranteed quadruple-precision floats. GNU C does not seem to support the math functions in libquadmath, such fabsq (absolute value, q being the suffix for quad).
Is there any way to get these functions working in C++, or is there some alternative library that I could use for math functions with __float128? What is the best method for getting quadruple-precision floats working in the GCC? Right now, I can add, subtract, and multiply them, but this is useless to me, considering how I have no way to convert them to strings or use functions such as truncq and fabsq to create my own string function.
Apparently, this seems to have been an installation error on my part.
While the core C/C++ portion of the GCC includes libquadmath.so, the Fortran version supplies libquadmath.a and quadmath.h, which can be included to access the functions.
#include <quadmath.h>
#include <iostream>
int main()
{
char* y = new char[1000];
quadmath_snprintf(y, 1000, "%Qf", 1.0q);
std::cout << y << std::endl;
return 0;
}