Proposal: Better power for Rational
daniel.is.fischer at web.de
Mon Oct 4 10:00:53 EDT 2010
On Monday 04 October 2010 11:57:06, Simon Peyton-Jones wrote:
> | I'll try to create a patch, however I may need some assistance
> | compiling base libraries.
> Thank you. Creating a patch, attaching to a ticket with some rationale,
> and submitting it to the libraries list, is the best way to push your
> work over the hill and into the actual code base. I'm sure others will
> help. If you get stuck, yell!
> Daniel Fischer is working in this patch too.
Since I'm working on GHC.Float anyway, I'll include Henning's rounding etc.
Speaking of GHC.Float, there are a few points where I would like some
guidance on where to put things.
I could of course put everything in GHC.Float, but it's big already and I'd
prefer not to clutter it up further.
For toRational, to avoid wasting time in gcd, I need an array for the
number of trailing 0-bits in a byte. Also, since bit-fiddling of Integers
is considerably slower than for fixed width types, I'd need to import
GHC.IntWord64 since a Double mantissa won't fit in an Int on 32-bit
systems. This could go into GHC.Float or into a GHC.Float.Utils module.
For fromRational, I need a fast integerLog2. For that, I need access to the
internal representation of Integers when using integer-gmp and an
alternative implementation for integer-simple (which would be much slower,
but if you use integer-simple, performance probably isn't your foremost
concern). I might need a few more odds and ends if special-casing for the
results of toRational (whose denominator is a power of 2) proves to be a
Putting all the auxiliary stuff in GHC.Float wrapped in #ifdefs is IMO an
integerLog2 and more generally integerLogBase are useful enough to be added
to GHC.Integer (Int/Word is not yet available, so it'd be the '#' versions,
where would the wrappers returning an Int or Word go?).
If I need the stuff for special casing, my preferred solution would be to
put it in GHC.Integer.Variant.Internals or add a small dedicated module for
them to the package.
So what's the best place to put stuff?
More information about the Libraries