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[Bug middle-end/51446] -fno-trapping-math generates NaN constant with different sign
- From: "joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 08 Dec 2011 20:37:11 +0000
- Subject: [Bug middle-end/51446] -fno-trapping-math generates NaN constant with different sign
- Auto-submitted: auto-generated
- References: <bug-51446-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51446
--- Comment #12 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-12-08 20:37:11 UTC ---
I think the soft-fp code tries to generate particular target-specific NaNs
because it's also used in the Linux kernel emulation of floating-point
instructions - which is a use case where doing the same as particular
hardware is desirable.
At the level of GCC compiling C code, the compiler provides the language
semantics. It doesn't provide the semantics of any particular choice of
instructions someone might expect to be used to implement the source code
- and in particular doesn't guarantee any choice of NaN where the language
(and IEEE 754 as applicable) don't determine the choice of NaN.