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[Bug libgcc/59714] complex division is surprising on aarch64
- From: "michael.hudson at linaro dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 08 Jan 2014 22:09:33 +0000
- Subject: [Bug libgcc/59714] complex division is surprising on aarch64
- Auto-submitted: auto-generated
- References: <bug-59714-4 at http dot gcc dot gnu dot org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59714
--- Comment #4 from Michael Hudson-Doyle <michael.hudson at linaro dot org> ---
OK, so I should stop talking about accurate and instead talk about surprising
:-)
I think it is pretty surprising that x/x != 1+0i for (I think) all x where the
ratio between the real and imaginary parts is not a power of 2 (put another
way, an error of 1ulp when the accurate result is 0 is more surprising than
when the accurate result is non-zero).
In general, fma makes it hard to reason about expressions like "a*b-c*d" --
which of the multiplications is being done at the higher precision? But I
guess arguing to fp-contract to default to off is a war I don't want to get
into fighting.