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Re: [Toon-members] Precision in SE3::exp()
From: |
Gerhard Reitmayr |
Subject: |
Re: [Toon-members] Precision in SE3::exp() |
Date: |
Wed, 28 Mar 2012 22:38:38 +0200 |
On 28 Mar 2012, at 19:25, Simon Taylor wrote:
> Howdy all,
>
> I've just been tracking down an unexpected change in output after some
> refactoring, and the root cause is fixed by the attached patch.
>
ok, so the problem is with the patch or without ?
> When precision is float, it is implicitly converted to double and double
> ::cos(double) is called, and the rest of that expression will also be
> promoted to double. My refactoring removed a "using namespace std" so the
> std::cos(float) overload was (IMHO correctly) used in my previous code.
> SE3::exp already has a "using std::sqrt;" statement, so style should probably
> be matched when it's fixed.
>
it should probably be done similar to sqrt:
using std::cos, std::sin;
and later sin(Precision p)
This is useful, if Precision is something completely different, for example
automatic differentiation class (like FADBAD++ that I am using). then the
compiler will also look in the namespaces of the Precision type to find a
matching sin overload. Otherwise, if there isn't one in std:: it will fail.
but, I tried to test this with FADBAD++ and it didn't fail :/
In anycase shouldn't there be a warning, then the double expression is assigned
to the float value at the end ? this should provide some heads-up that there is
something going on.
cheers,
Gerhard
> I've been trying to find a list of C++ overloads that are added std to search
> for all potential occurrences of these sorts of issues but I haven't had much
> luck. There's a couple of gcc options that help tracking them down in code
> that actually gets compiled (-Wdouble-promotion and -Wconversion) but I don't
> think there's a warning for implicit parameter conversion (I can't make
> "double v = ::sqrt(1.3f);" generate any warnings, but having v as a float
> makes -Wconversion pick it up as possible data loss).
>
> Simon
>
> ps: since the git switch we seem to have lost commit email notifications...
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--
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Gerhard Reitmayr
Institute for Computer Graphics and Vision
http://www.icg.tugraz.at/Members/gerhard
tel: ++43 316 873 5082