From: Stefan Monnier <monnier@iro.umontreal.ca>
To: "Vincent Belaïche" <vincent.b.1@hotmail.fr>
Cc: cyd@stupidchicken.com, emacs-devel <emacs-devel@gnu.org>
Subject: Re: Code for converting between Elisp and Calc floats
Date: Tue, 27 Oct 2009 02:16:07 -0400 [thread overview]
Message-ID: <jwvocnte5aa.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <BLU104-W109BFD7C264619CEFBFC9184B90@phx.gbl> ("Vincent Belaïche"'s message of "Tue, 27 Oct 2009 05:56:50 +0100")
> For the C code anyhow, even if the integer component word size was not
> passed along in the interface, you would have anyhow to manage strange
> word sizes. This is because the mantissa is 53 bits, and 53 is not
> a multiple of 16. Also the mantissa is not aligned on the double word
> boundary (the sign + exponent not being a muliple of 16 bits) and you
> also have this phantom bit case to handle.
I think if you use frexp+floor, most of those issues won't matter much.
>> I think it fits better in C. Basically, it would be the equivalent to
>> C's frexp.
> C++' frexp and ldexp are not a direct alternative,
I understand. The interface you proposed is closer to what we'd like
than what frexp has to offer.
> Another alternative would be that frexp and ldexp and suhlikes are
> made builtin functions, and that the construct-float,
> deconstruct-float functions are in Lisp using those builtins: that
> would indeed be my preference if everyone thinks that the submitted
> C code is too complex.
Actually my preference would be to keep the functionality you proposed
(i.e. two functions (de)construct-float written in C), except force the
base to be 65536 (i.e. 16bits per integer), and rewrite the C code to
use standard functions like frexp, floor, isnan, and friends.
Stefan
next prev parent reply other threads:[~2009-10-27 6:16 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-27 4:56 Code for converting between Elisp and Calc floats Vincent Belaïche
2009-10-27 6:16 ` Stefan Monnier [this message]
2009-10-27 19:38 ` Vincent Belaïche
-- strict thread matches above, loose matches on Subject: below --
2009-10-08 20:47 allow C-x v i / C-x v v to create a repository if none is available Dan Nicolaescu
2009-10-09 19:18 ` Stefan Monnier
2009-10-22 18:56 ` Code for converting between Elisp and Calc floats Jay Belanger
2009-10-22 20:04 ` James Cloos
2009-10-23 0:50 ` Stefan Monnier
2009-10-24 20:03 ` Jay Belanger
2009-10-25 0:56 ` Stefan Monnier
2009-10-25 5:36 ` David Kastrup
2009-10-25 11:36 ` Vincent Belaïche
2009-10-25 14:11 ` Chong Yidong
2009-10-25 19:29 ` Vincent Belaïche
2009-10-26 2:30 ` Stefan Monnier
2009-10-26 12:48 ` Vincent Belaïche
2009-10-27 3:22 ` Stefan Monnier
2009-10-25 13:57 ` Stefan Monnier
2009-10-25 18:35 ` Eli Zaretskii
2009-10-23 13:11 ` Richard Stallman
2009-10-23 13:26 ` David Kastrup
2009-10-24 17:34 ` Richard Stallman
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