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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/109818] std::trunc() requires a <cmath> hack after
 building DJGPP
Date: Fri, 12 May 2023 21:21:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109818

--- Comment #19 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #15)
> A proper fix would be to split up the configure test for USE_C99_MATH_TR1=
 to
> be more fine-grained, so that we use the subset of functions that are
> supported, instead of all or nothing.

Ugh, the set of functions defined by djgpp's <math.h> seems really arbitrat=
y.

exp2 only has the double form, not float or long double.
expm1 has double and float forms, not long double.
trunc has all three forms.

Even within a group like the Gamma functions, lgamma and lgammaf are present
(but no lgammal) but none of tgamma, tgammaf and tgammal are present.

So there's no clear way to split them up into groups that can be tested
together, it ends up just being incredibly djgpp-specific (and we might as =
well
just manually add #ifndef __DJGPP__ in very specific places).=