The MPFR library is a C library for multiple-precision floating-point
computations with exact rounding (also called correct rounding).  It
is based on the GMP multiple-precision library.

The main goal of MPFR is to provide a library for multiple-precision
floating-point computation which is both efficient and 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).

WWW: https://www.mpfr.org/