Type and Macro Changes (GNU MPFR 4.2.1)
Description: How to install and use GNU MPFR, a library for reliable multiple precision floating-point arithmetic, version 4.2.1.

### 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). Faithful rounding (`MPFR_RNDF`) was added in MPFR 4.0, but currently, it is partially supported.

The flags-related macros, whose name starts with `MPFR_FLAGS_`, were added in MPFR 4.0 (for the new functions `mpfr_flags_clear`, `mpfr_flags_restore`, `mpfr_flags_set` and `mpfr_flags_test`, in particular).