From: nisse@lysator.liu.se (Niels Möller)
To: Mark H Weaver <mhw@netris.org>
Cc: 10519@debbugs.gnu.org, "Ludovic Courtès" <ludo@gnu.org>,
"Torbjorn Granlund" <tg@gmplib.org>
Subject: bug#10519: guile and (mini-)gmp
Date: Tue, 26 Mar 2013 09:17:38 +0100 [thread overview]
Message-ID: <nnboa6mv6l.fsf@stalhein.lysator.liu.se> (raw)
In-Reply-To: <87620ph8yu.fsf@tines.lan> (Mark H. Weaver's message of "Sun, 17 Mar 2013 20:01:29 -0400")
Mark H Weaver <mhw@netris.org> writes:
> FYI, I've pushed patches to Guile's git repository (stable-2.0 branch)
> which eliminate the known obstacles to mini-gmp integration.
Out of curiosity, I had a quick look at the patches as posted to the
guile devel list.
For the small integer gcd code, you may want to have a look at the
tricks used in
http://gmplib.org:8000/gmp/file/304af17b9ccc/mpn/generic/gcd_1.c, the
code under GCD_1_METHOD == 2
1. Shift out the least significant bit of both a and b (they're always
one). Maybe you don't need this of you have some extra bits already
(signed types, or some bits reserved for type info).
2. Then, the sign bit of a - b correctly gives the result of the
comparison a < b. Constructing a mask from this difference is then a
simple right shift (if >> on a signed int is not an arithmetic right
shift, you need shift and a negation).
3. Use this bit mask when forming the absolute value |a - b|, and when
swapping values around, to avoid unpredictable branches which
typically are quite expensive.
Regards,
/Niels
--
Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
Internet email is subject to wholesale government surveillance.
next prev parent reply other threads:[~2013-03-26 8:17 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-15 21:22 bug#10519: guile and (mini-)gmp Niels Möller
2012-01-16 10:19 ` Mark H Weaver
2012-01-16 14:06 ` Niels Möller
2012-01-16 19:21 ` Mark H Weaver
2012-01-28 9:49 ` Niels Möller
2012-01-28 10:10 ` Mark H Weaver
2012-07-22 9:04 ` Ludovic Courtès
2012-02-03 13:40 ` Andy Wingo
2012-02-03 19:56 ` Niels Möller
2012-02-03 20:01 ` Torbjorn Granlund
2012-02-04 22:46 ` Ludovic Courtès
2012-07-22 9:00 ` Ludovic Courtès
2012-07-22 23:17 ` Niels Möller
2012-08-10 21:51 ` Ludovic Courtès
2012-08-11 9:37 ` Niels Möller
2012-08-11 19:46 ` Ludovic Courtès
2012-08-11 21:50 ` Niels Möller
2012-08-11 22:48 ` Ludovic Courtès
2013-03-02 20:04 ` Andy Wingo
2013-03-02 20:58 ` Mark H Weaver
2013-03-05 19:09 ` Mark H Weaver
2013-03-18 0:01 ` Mark H Weaver
2013-03-18 9:19 ` Ludovic Courtès
2013-03-26 8:17 ` Niels Möller [this message]
2013-03-27 17:00 ` Mark H Weaver
2016-10-27 12:29 ` Niels Möller
2016-11-10 19:56 ` Andy Wingo
2013-03-02 21:45 ` Niels Möller
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