GMP bug - mpf_get_str for very small numbers [read this, not former1]

[Rezac David]

Hello again!

I'm very sorry for the previous letter. That one is probably the most
impossible ever. I don't know what I was thinking when I was writing that.
I mixed few things together, so now I send something [hopefully] better.

The problem is with numbers that are very small. Like in this example:

  a = "1e-2147483640";
  cout << a << "\n";    //works's
  a=a*a;
  cout << a << "\n";    //doesn't

In the function mpf_get_str() [file mpf/get_str.c] some asserts fail
and the conversion kills the program.

The output is:
 0.1e-2147483639
get_str.c:374: GNU MP assertion failed: tstr[0] != 0
Ended with failure (SIGABRT) (core dumped)
----------------------------

When I use "1e+214783640" in the same code, the exponent becomes negative
but no assertion-related problems show up. [Well, don't mention that the
result is unusable~]

>From what I found out, the exponent is stored in long int, and I haven't
noticed any detection of its over-/under-flow. [Of course that when it
underflows, the number should go to 0.0, not infinity as I wrote. To
+/-infinity it goes when it overflows, right?]. Well might it be that way
or another, the point is that the extreme values are not handled properly
[as it seems to me].

Well, I hope I didn't messed things again and that this will help you to
fix the problem.

Thank you for your patience.

With regards,
David Rezac

P.S.: the code of the machar() function [determines the info about the FP
arithmetics] is in the book "Numerical Recipes in C", chapter 20-1. It's
available in .ps on web [don't remember the URL, try www.google.com].

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