cpp_dec_float<N>

boost/multiprecision/cpp_dec_float.hpp

10

None

Header only, all C++ implementation. Boost licence.

Approximately 2x slower than the MPFR or GMP libraries.

mpf_float<N>

boost/multiprecision/gmp.hpp

2

GMP

Very fast and efficient back-end.

Dependency on GNU licensed GMP library.

mpfr_float<N>

boost/multiprecision/mpfr.hpp

2

GMP and MPFR

Very fast and efficient back-end, with its own standard library implementation.

Dependency on GNU licensed GMP and MPFR libraries.

float128

boost/multiprecision/float128.hpp

2

Either libquadmath or the Intel C++ Math library.

Very fast and efficient back-end for 128-bit floating point values (113-bit mantissa, equivalent to FORTRAN's QUAD real)

Depends on the compiler being either recent GCC or Intel C++ versions.