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From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/98384] [11 Regression] new test case
 20_util/to_chars/long_double.cc in r11-6249 fails on powerpc64 BE
Date: Mon, 08 Mar 2021 17:42:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98384

--- Comment #24 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to David Edelsohn from comment #23)
> The AIX failure is:
>=20
> printf_buffer=3D
> 1.
> 4426950408889633870046509400708600880000000000000000000000000000000000000=
0000
> 00000000000000000000000=20
>=20
> to_chars_buffer=3D
> 1.
> 4426950408889633870046509400708600878715515136718750000000000000000000000=
0000
> 00000000000000000000000??/?P00001.
> 4426950408889633870046509400708600880000000000000000000000000000000000000=
0000
> 00000000000000000000000
>=20
> output_length=3D
> 102
>=20
> ./long_double.cc:194: void test02(): Assertion '!memcmp(printf_buffer,
> to_chars_buffer, output_length)' failed.

I managed to reproduce this issue on AIX (gcc119).  It looks like the %e/%f=
/%g
specifiers (as well as %Le/%Lf/%Lg -- long double is equivalent to double)
never output more than 37 significant decimal digits on AIX.

For e.g.

  printf("%.53e\n", 0x1.71547652b82fep+0);
  printf("%.0f\n", 0x1.249ad2594c37dp+332);

x86 glibc printf outputs

  1.44269504088896338700465094007086008787155151367187500e+00
=20
100000000000000001590289110975991804683608085639452813897813275577478387721=
70381060813469985856815104

and AIX printf outputs

  1.44269504088896338700465094007086008800000000000000000e+00
=20
100000000000000001590289110975991804700000000000000000000000000000000000000=
00000000000000000000000000

It seems to me the output of AIX printf is wrong/nonconforming here..=