droundy:
On Mon, Jun 16, 2008 at 05:08:36PM -0700, Don Stewart wrote:
droundy:
On Mon, Jun 16, 2008 at 04:50:05PM -0700, John Meacham wrote:
On Mon, Jun 16, 2008 at 04:41:23PM -0700, Evan Laforge wrote:
But what about that NaN->Integer conversion thing?
I think that may be a bug or at least a misfeature. The standard is somewhat vauge on a lot of issues dealing with floating point since it is such a tricky subject and depends a lot on the environment. The various rounding funcitons are particularly ugly IMHO. I added varients of them that preserved the floating point type and properly implemented IEEE behavior for jhc.
I think the Data.Binary guys think it's a feature, since they rely in this behavior (well, they rely on the equivalently-foolish behavior of toRational). I think it's a bug.
You mean:
instance Binary Double where put d = put (decodeFloat d) get = liftM2 encodeFloat get get
?
if you've a portable Double decoding that works in GHC and Hugs, I'm accepting patches.
I really don't understand why being portable is such an issue. Is it really better to behave wrong on every platform rather than behaving wrong on a very small minority of platforms?
The Binary instances are required to be portable, as that's the part of the definition of Binary's mandate: a portable binary encoding.
Anyhow, I've not hacked on binary, because I've not used it, and have trouble seeing when I would use it. So maybe I shouldn't have brought the subject up, except that this use of decodeFloat/encodeFloat is a particularly egregious misuse of floating point numbers.
decodeFloat really ought to be a partial function, and this should be a crashing bug, if the standard libraries were better-written.
It's a bug in the H98 report then:
Section 6.4.6:
"The function decodeFloat applied to a real floating-point number returns
the significand expressed as an Integer and an appropriately scaled
exponent (an Int). If decodeFloat x yields (m,n), then x is equal in value
to mb^n, where b is the floating-point radix, and furthermore, either m
and n are both zero or else b^d-1<=m