From: "Yaron Minsky" <yminsky@cs.cornell.edu>
To: caml-list@inria.fr
Subject: [Caml-list] Weird behavior with nan's and min/max
Date: Tue, 14 Oct 2003 10:37:14 -0400 (EDT) [thread overview]
Message-ID: <51792.141.155.88.179.1066142234.squirrel@minsky-primus.homeip.net> (raw)
min and max have pretty strange behavior when it comes to nan's. Here's
an example:
# min 3. nan;;
- : float = 3.
# min nan 3.;;
- : float = nan
When you think about it, the reason for this is clear. comparisons
involving nan's always return false, so if you simply implement min as
follows:
if x < y then x else y
the the result will depend on the order.
Now here's the weird bit. I decided I wanted a polymorphic comparison
that wouldn't have this problem. But this is a little harder than it
seems, since it turns out that specialized float version of equality is
different from the polymorphic version. Here's the example:
# let raw_min = min
val raw_min : 'a -> 'a -> 'a = <fun>
# let min x y =
if not (y = y) then y
else if not (x = x) then x
else raw_min x y
;;
val min : 'a -> 'a -> 'a = <fun>
# let fmin (x:float) y =
if not (y = y) then y
else if not (x = x) then x
else raw_min x y
;;
val fmin : float -> float -> float = <fun>
# fmin 3. nan;;
- : float = nan
# fmin nan 3.;;
- : float = nan
# min nan 3.;;
- : float = nan
# min 3. nan;;
- : float = 3.
So, does this count as a bug? Any ideas about how to fix this behavior in
a reasonably efficient way?
Yaron
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next reply other threads:[~2003-10-14 14:37 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-14 14:37 Yaron Minsky [this message]
2003-10-14 14:56 ` Yaron Minsky
2003-10-14 20:52 ` Yaron Minsky
2003-10-14 23:43 ` skaller
2003-10-16 17:29 ` Hendrik Tews
2003-10-16 13:16 ` Xavier Leroy
2003-10-16 14:01 ` Yaron Minsky
2003-10-17 9:26 ` [Caml-list] Test nan (was: Weird behavior with nan's and min/max) Christophe TROESTLER
2003-10-16 21:40 ` [Caml-list] Weird behavior with nan's and min/max Yaron Minsky
2003-10-16 21:50 ` Yaron Minsky
2003-10-16 22:52 ` Damien Doligez
2003-10-17 14:55 ` skaller
2003-10-17 15:14 ` Floating point exceptions (Was Re: [Caml-list] Weird behavior with nan's and min/max) Yaron Minsky
2003-10-17 23:55 ` [Caml-list] Weird behavior with nan's and min/max Yaron M. Minsky
2003-10-20 13:29 ` Xavier Leroy
2003-10-20 13:43 ` Yaron Minsky
2003-10-20 14:24 ` Xavier Leroy
2003-10-16 23:55 ` [Caml-list] " Jed Davis
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