Comment 10 for bug 1745188

Hello,

I encountered this abort/crash with gnome-calculator and finally got rid of it as under.

I manually built and installed the latest mpfr/mpfc/gmp source code and binaries for
building gcc-7.3 which turned out to be extremely frustrating and energy-draining.
So, after installing those hand-built mpfr/mpfc/gmp binaries, I happened to launch the calculator(gnome-calculator) from the quick launch side-bar(yes, I still have Unity on
17.10!) and its icon was animating as usual for few seconds and nothing was happening
after that. So, I tried to launch it from terminal - it showed the abort/crash error
that this bug reports :
"../../src/init2.c:52: MPFR assertion failed: p >= 2 && p <= ((mpfr_prec_t)((mpfr_uprec_t)(~(mpfr_uprec_t)0)>>1))".

After searching for the above error, I stumbled upon this bug report, and I tried to
downgrade back to the default Ubuntu-repo version via "apt install" - that didn't solve
the issue. I tried to build and install mpfr-4.0.0 version - didn't change the crash behavior.
Tried building and installing mpfr-3.1.6/5 - didn't work. Manually removed the installed
libraries(libmpfr*) from /usr/lib/* and /usr/local/lib/* and redid the installation - both
"apt install" and build-install method from source for the reported mpfr-3.1.6 - didn't help.
I had also tried to modify mpfr-4.0.1's source code to use precision 2 instead of 1 and also
bunch of the other assert-macros logic for disabling the assertion(abort) - didn't help.

Downgraded mpc* as well as gmp* to older versions by building from their sources and installing
them - didn't help.

So, basically, I tried to put my system back to the previous state before I started meddling
with the mpfr/gmp/mpc all for building gcc-7.3 from its source - huge cost paid!

Tried the extreme cases out though not relevant as I could already figure out but did them
anyway to get back the "calculator" : reinstalled the kernel(I know kernel has nothing
to do with mpfr!), rebooted the PC, and so on - didn't help.

Finally, I paid close attention to the error stating that this assertion was from "init2.c:52",
so I located this 52nd source code line inside mpfr-3.1.6/src/init2.c and *disabled* the
assertion by commenting it out as my last attempt to get back the system to successfully
launch gnome-calculator, rebuilt and installed it - boom! I got the gnome-calculator back.
Below is what I commented out. I thought this was not necessary as MPFR_PREC_MIN was already 2
and not 1 as mentioned here in this proposed bug report/fix. Anyway.

<snip>
  /* p=1 is not allowed since the rounding to nearest even rule requires at
     least two bits of mantissa: the neighbours of 3/2 are 1*2^0 and 1*2^1,
     which both have an odd mantissa */
  //MPFR_ASSERTN(p >= MPFR_PREC_MIN && p <= MPFR_PREC_MAX);
</snip>

I confirmed that MPFR_PREC_MIN was 2 as told in here in this bug report and not 1 as in 4.0.1.
But, even then the above assertion was failing causing abort/crash for gnome-calculator.
Below is what I have in mpfr-3.1.6/src/mpfr.h(unchanged).

<snip>
/* Definition of precision limits without needing <limits.h> */
/* Note: the casts allows the expression to yield the wanted behavior
   for _MPFR_PREC_FORMAT == 1 (due to integer promotion rules). */
#define MPFR_PREC_MIN 2
#define MPFR_PREC_MAX ((mpfr_prec_t)((mpfr_uprec_t)(~(mpfr_uprec_t)0)>>1))
</snip>

Hope my above change help those banging their head to fix this super-annoying
crash, until it's fixed in the mpfr* codebase/release as needed.

Cheers,
Raghavan