6.1 Type and Macro Changes

The official type for exponent values changed from mp_exp_t to mpfr_exp_t in MPFR 3.0. The type mp_exp_t will remain available as it comes from GMP (with a different meaning). These types are currently the same (mpfr_exp_t is defined as mp_exp_t with typedef), so that programs can still use mp_exp_t; but this may change in the future. Alternatively, using the following code after including ‘mpfr.h’ will work with official MPFR versions, as mpfr_exp_t was never defined in MPFR 2.x:

#if MPFR_VERSION_MAJOR < 3
typedef mp_exp_t mpfr_exp_t;
#endif

The official types for precision values and for rounding modes respectively changed from mp_prec_t and mp_rnd_t to mpfr_prec_t and mpfr_rnd_t in MPFR 3.0. This change was actually done a long time ago in MPFR, at least since MPFR 2.2.0, with the following code in ‘mpfr.h’:

#ifndef mp_rnd_t
# define mp_rnd_t  mpfr_rnd_t
#endif
#ifndef mp_prec_t
# define mp_prec_t mpfr_prec_t
#endif

This means that it is safe to use the new official types mpfr_prec_t and mpfr_rnd_t in your programs. The types mp_prec_t and mp_rnd_t (defined in MPFR only) may be removed in the future, as the prefix mp_ is reserved by GMP.

The precision type mpfr_prec_t (mp_prec_t) was unsigned before MPFR 3.0; it is now signed. MPFR_PREC_MAX has not changed, though. Indeed the MPFR code requires that MPFR_PREC_MAX be representable in the exponent type, which may have the same size as mpfr_prec_t but has always been signed. The consequence is that valid code that does not assume anything about the signedness of mpfr_prec_t should work with past and new MPFR versions. This change was useful as the use of unsigned types tends to convert signed values to unsigned ones in expressions due to the usual arithmetic conversions, which can yield incorrect results if a negative value is converted in such a way. Warning! A program assuming (intentionally or not) that mpfr_prec_t is signed may be affected by this problem when it is built and run against MPFR 2.x.

The rounding modes GMP_RNDx were renamed to MPFR_RNDx in MPFR 3.0. However the old names GMP_RNDx have been kept for compatibility (this might change in future versions), using:

#define GMP_RNDN MPFR_RNDN
#define GMP_RNDZ MPFR_RNDZ
#define GMP_RNDU MPFR_RNDU
#define GMP_RNDD MPFR_RNDD

The rounding mode “round away from zero” (MPFR_RNDA) was added in MPFR 3.0 (however no rounding mode GMP_RNDA exists).