Re: Float comparison

CBFalconer said:

Richard Heathfield wrote:
CBFalconer said:
Keith Thompson wrote:
Joe Wright <joewwright@xxxxxxxxxxx> writes:
Keith Thompson wrote:
Joe Wright <joewwright@xxxxxxxxxxx> writes:

[...]
float x = 0.3333333432674407958984375;
float y = 3.33333343e-01;

... snip ...

The approximation 0.333333343, though it's perfectly fine in
most contexts, doesn't demonstrate this.

Yes it does. Both the value above are members of the same
range,

There are infinitely many ranges of which both values are
members.

which is the range specified by the floating object when
initialized with either value.

No, the floating point object doesn't specify a range. It is able
to store a value, but only one value at a time. We covered this
before.

No.

We did, actually.

Maybe you misstated it before.

No, I stated it before. So did several others.

The point is that a given FP
system always specifies a range covered by a particular FP value.

The point is that it doesn't.

The mere fact that you say this indicates you haven't a clue as to
what is really going on.

C&V, please. RELEVANT C&V.

Which is also why (x == y) is evaluated as true.

It's evaluated as true when x has the same value as y.

The only difference is in the programming which initialized
them.

The programming which initialized them doesn't matter as far as
their value is concerned. The thing that affects their value is,
would you believe, the last value to be stored there. If that's
the same for both, both will store the same value. In this case,
the value stored in y is the result of converting a
double-precision floating-point value such as (on my system)
0.333333343000000004163752009844756685197353363037109375 into a
single-precision floating point value.

You just attempted to specify the programming. Wrong. The only
thing available is the FP object itself.

No, I pointed out that the value stored is the value stored. I would
not trouble anyone else with such a redundancy, but it seems you
are having trouble understanding it.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999
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