Re: Can you specialize the Template operator==

From:

3DCoderGuy <nobody@nospam.com>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 09 May 2008 10:38:30 -0700

Message-ID:

<uEeZAufsIHA.4260@TK2MSFTNGP05.phx.gbl>

Alf P. Steinbach wrote:

* 3DCoderGuy:

>> Snip...

Others have remarked on syntax etc.

However, if you really want to do this epsilon thing (note: it means you
lose the important property that a==b && b==c implies a==c, which means
it's really not a good idea, at least as long as you pretend that it's
'==' equality), then I suggest you pick up the relevant epsilon from a
template:

<code>
template< typename T >
struct EpsilonFor
{
static T const value;
};

template<>
float const EpsilonFor<float>::value = 1.e-4f;

template<>
double const EpsilonFor<double>::value = 1.e-6;

template< typename FloatType >
bool isNearEqual( FloatType a, FloatType b )
{
return (std::abs( a - b ) <= EpsilonFor<FloatType>::value);
}
</code>

Cheers, & hth.,

- Alf

PS: Are you aware of std::numeric_limits? If not, take a look.

What took you so long Alf. I was wondering how to do just what you're
suggesting.

Thanks a ton.

I wasn't aware of the std::numeric_limits. I'm very green when it comes
to std. I've used std containers and only very limited.

I noticed you use the abs method. Back in the day when optimization was
important (and is become so again), I wouldn't use the abs because of
the call which used a lot of cycles ( I really don't know if that is
still true today. I haven't written assembler since 80486s). Doing the
(x1 - x2 < EPSILON) && (...) would mean that the test on points that
were different would fail on the first difference. Do you have any
comments on this? I take from you last discussion regarding wasted
copies to temp objects that optimization is important to you.

Thanks again Alf.
Mark