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From: "joseph at codesourcery dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/103406] [12 Regression] gcc -O0 behaves differently
 on "DBL_MAX related operations" than gcc -O1 and above
Date: Wed, 24 Nov 2021 22:22:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103406

--- Comment #11 from joseph at codesourcery dot com <joseph at codesourcery=
 dot com> ---
The sign of a NaN result is never specified in C except for fabs,=20
copysign, negation, unary + (and assignment to the same format in the case=
=20
where that's copy rather than convertFormat).

The result should of course be NaN (of any sign), not 0.

The reason soft-fp (and thus sfp-machine.h) has special support for=20
choosing a NaN result based on NaN operands is because soft-fp is also=20
used in the Linux kernel for emulating floating-point instructions, and in=
=20
that context the aim is to follow the semantics of those instructions,=20
which specifies things left unspecified in IEEE 754 and its C bindings.=20=
=20
That isn't relevant at the level of C code or libgcc functions.=