Re: Setting floating point variable as infinite

Victor Bazarov <v.bazarov@comcast.invalid>
Fri, 23 Mar 2012 11:50:16 -0400
On 3/23/2012 11:03 AM, Rui Maciel wrote:

Victor Bazarov wrote:

The usual way to find the minimum is to initialize the value from the
first element, and then start comparing from the second element. An
empty set is a special case for which the calculation of the "minimum"
should just throw an exception. A set of one element is also a special
case: there is no need to compare anything. Two elements could be
made into a special case by use of std::min.

I was hoping to use a single loop.

Are you concerned with less typing, and not with implementing it
correctly *logically*? Do you consider "a single loop" better or more
efficient in some way?

 > Relying on a separate initialization

block feels a bit like a crude-ish hack.

"Crude-ish"? Really? <shrug> Using an infinity value in that manner is
crudish, IMNSHO. It suggests that (a) infinity is not a valid value for
any set element to be associated with (which might be true in your
model, but doesn't necessarily sound right in all cases), and (b) that
the maximum value from the elements of an empty set is infinity, which
is a number (if you divide by it, you get 0). I'd probably use NaN for
that, although by definition of "seeking a maximum associated floating
point number" should *not* be allowed for an empty set, such search
shouldn't return a value.

As for infinity (unrelated to searching through a set of numbers), there
is 'std::numeric_limits<double>::infinity()', which you could call if
'std::numeric_limits<double>::has_infinity' is 'true'.

Yes, I was using that, and according to the standard
std::numeric_limits<T>::has_infinity is true for T = float and double, so no
test is necessary. The only problem I have with it is that it doesn't feel
quite right to handle infinity values like this. At least I never saw this
being done anywhere else.

<another shrug> I have. But it's still not right. You can use any
other designated value that can never be found in your set. And if you
don't have any identifiable value to use, don't. Use *logic*.
Essentially you're trying to have a mapping of yourtype values to
double/float values without

     std::map<double, yourtype const*> yourmap;

.. And you're trying to figure out a hack to get
(*yourmap.rbegin()).first without checking whether the 'yourmap' is
empty or not. <third shrug>

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