Rounding error

[Frank Heckenbach]

mpf_get_str seems to round incorrectly sometimes.
In this test program, the digits around 809 are "...244594553...",
so it should round to "...244595", but it outputs "...244594".

#include <gmp.h>
#include <stdio.h>

int main (void)
{
  mpf_t pi;
  mp_exp_t e;
  mpf_set_default_prec (10000);  // much more than sufficient
  mpf_init_set_str (pi, "3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051320005681271452635608277857713427577896091736371787214684409012249534301465495853710507922796892589235420199561121290219608640344181598136297747713099605187072113499999983729780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473035982534904287554687311595628638823537875937519577", 10);
  puts (mpf_get_str (NULL, &e, 10, 809, pi));
}

- gmp 6.2.1, original release, unpatched, no configure options

- configure: summary of build options:

  Version:           GNU MP 6.2.1
  Host type:         zen2-pc-linux-gnu
  ABI:               64
  Install prefix:    /usr/local
  Compiler:          gcc
  Static libraries:  yes
  Shared libraries:  yes

- gcc -v

  Using built-in specs.
  COLLECT_GCC=gcc
  COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
  OFFLOAD_TARGET_NAMES=nvptx-none
  OFFLOAD_TARGET_DEFAULT=1
  Target: x86_64-linux-gnu
  Configured with: ../src/configure -v --with-pkgversion='Debian 8.3.0-6' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release \
    --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
  Thread model: posix
  gcc version 8.3.0 (Debian 8.3.0-6)

- uname -a

  Linux mars 5.6.0-0.bpo.2-amd64 #1 SMP Debian 5.6.14-2~bpo10+1 (2020-06-09) x86_64 GNU/Linux

- ./config.guess

  zen2-pc-linux-gnu

- ./configfsf.guess

  x86_64-pc-linux-gnu

- CPU: AMD Ryzen 9 3900X 12-Core Processor