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From: "mikael at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/66311] [5/6 Regression] Problems with some integer(16) values
Date: Tue, 04 Aug 2015 10:07:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66311

Mikael Morin <mikael at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mikael at gcc dot gnu.org

--- Comment #7 from Mikael Morin <mikael at gcc dot gnu.org> ---
(In reply to Francois-Xavier Coudert from comment #6)
> I tracked the issue to the two calls to wi::from_mpz() and
> wide_int_to_tree() in gcc/fortran/trans-const.c:gfc_conv_mpz_to_tree().
> There the mpz value (which is correct) in translated into:
> 
>   wide_int_storage = {
>     val = ([0] = -2, [1] = 0, [2] = 56)
>     len = 1
>     precision = 128
>   }
> 
> which appears to be where the -2 comes from.

And in wi::from_mpz it probably comes from the mpz_sizeinbytes and mpz_export
functions not paying attention to the sign, as stated in the documentation:

https://gmplib.org/manual/Integer-Import-and-Export.html
> The sign of op is ignored, just the absolute value is exported. An application
> can use mpz_sgn to get the sign and handle it as desired. (see Integer
> Comparisons) 

https://gmplib.org/manual/Miscellaneous-Integer-Functions.html#Miscellaneous-Integer-Functions
> The sign of op is ignored, just the absolute value is used.