_decimal:
o Make all "mpd_t to C integer" conversion functions available in both the
64-bit and the 32-bit versions.
o Make all mixed mpd_t/C integer arithmetic functions available in the
32-bit version.
o Better handling of __STDC_LIMIT_MACROS for C++ users.
o Add struct tags (at the request of C++ users).
2) Check for libmpdec.so.2 if --with-system-libmpdec is used.
required for a corner case in dec_hash() in the following commit and also
usually faster. dec_hash() needs some extra precision above MPD_MAX_PREC,
and _mpd_base_ndivmod() is not audited for that.
2) Use _mpd_basemul() if the length of the smaller operand is less than
or equal to 256. While this is technically an optimization, it is
required for *testing* corner cases in dec_hash() in reasonable time.
None of the _mpd_shortadd() or _mpd_shortmul() functions read uninitialized
values. Previously zeroing was required since _mpd_real_size() was called
on the output array.
use log10() to calculate the size of the output array. The current code
has been tested on x86/amd64 (and to a lesser extent on qemu-mips qemu-sparc)
and produces sufficiently large values for all inputs tested so far (coefficient
sizes of 10**18 - 1 are hard to test exhaustively).
The new code does not rely on the correctness of log10() and resizes
the output arrays if the allocated space is insufficient.
1) _mpd_qdivmod() uses the context precision only in two places, and
the new code should be exactly equivalent to the previous code.
2) Remove misleading comment.
3) The quotient *is* an integer with exponent 0, so calling mpd_qtrunc()
is pointless.
4) Replace two instances of identical code by a single one.
5) Use _mpd_cmp_abs() instead of mpd_cmp_total_mag(): the operands
are not special.
6) Don't clear MPD_Rounded in the status (with the current code it should
not be set within the function).
