initial import of MPFR 4.2.0. changes from 4.1.0 include:

Binary compatible with MPFR 4.0.* and 4.1.*, though some minor changes
in the behavior of the formatted output functions may be visible,
regarded as underspecified behavior or bug fixes (see below).

New functions mpfr_cosu, mpfr_sinu, mpfr_tanu, mpfr_acosu, mpfr_asinu,
mpfr_atanu and mpfr_atan2u.

New functions mpfr_cospi, mpfr_sinpi, mpfr_tanpi, mpfr_acospi,
mpfr_asinpi, mpfr_atanpi and mpfr_atan2pi.

New functions mpfr_log2p1, mpfr_log10p1, mpfr_exp2m1, mpfr_exp10m1 and
mpfr_compound_si.

New functions mpfr_fmod_ui, mpfr_powr, mpfr_pown, mpfr_pow_uj,
mpfr_pow_sj and mpfr_rootn_si (mpfr_pown is actually a macro defined as
an alias for mpfr_pow_sj).

Bug fixes.
- In particular, for the formatted output functions (mpfr_printf, etc.),
the case where the precision consists only of a period has been fixed to
be like .0 as specified in the ISO C standard, and the manual has been
corrected and clarified.
- The macros of the custom interface have also been fixed:
they now behave like functions (except a minor limitation for
mpfr_custom_init_set).

GNU mpfr 4.1.0. main changes from 4.0:

Changed __float128 to the type _Float128 specified in ISO/IEC TS 18661.
__float128 is used as a fallback if _Float128 is not supported.
New function mpfr_get_str_ndigits about conversion to a string of digits.
New function mpfr_dot for the dot product (incomplete, experimental).
New functions mpfr_get_decimal128 and mpfr_set_decimal128 (available
only when MPFR has been built with decimal float support).
New function mpfr_cmpabs_ui.
New function mpfr_total_order_p for the IEEE 754 totalOrder predicate.
The mpfr_out_str function now accepts bases from -2 to -36, in order to
follow mpfr_get_str and GMP's mpf_out_str functions (these cases gave an
assertion failure, as with other invalid bases).
Shared caches: cleanup; really detect lock failures (abort in this case).
Improved mpfr_add and mpfr_sub when all operands have a precision
equal to twice the number of bits per word, e.g., 128 bits on a 64-bit
platform.
Optimized the tuning parameters for various architectures.