The MPFR library is a C library for multiple-precision floating-point
computations with "correct rounding".
The MPFR is efficient and also has a well-defined semantics.
It copies the good ideas from the ANSI/IEEE-754 standard for double-precision floating-point arithmetic (53-bit mantissa).
MPFR is based on the GMP multiple-precision library. The library is available as 32-bit and 64-bit.