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aldot at gcc dot gnu dot org changed:
What|Removed |Added
OtherBugsDependingO||16996
nThis||
Sta
--- Comment #14 from vda dot linux at googlemail dot com 2006-08-04 18:14
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>But since these sort of transformations are of
>a very mathematical nature, I trust the author of the
>suggested changes has proven the algorithms?
I did not write a paper about it, but I think I have
the pr
--- Comment #13 from tege at swox dot com 2006-08-04 11:57 ---
Subject: Re: suboptimal 'division by constant' optimization
I looked briefly into the suggested change, without trying to
assess its correctness. But since these sort of transformations
are of a very mathematical nature, I
--- Comment #12 from vda dot linux at googlemail dot com 2006-08-03 17:06
---
Created an attachment (id=12005)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12005&action=view)
Alternative algorithm v. 3
Formatting fixes mostly
--
vda dot linux at googlemail dot com changed:
--- Comment #11 from amylaar at gcc dot gnu dot org 2006-08-02 19:34
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(In reply to comment #9)
> Thanks for the link to .pdf! Who's Tege? And his email address is ...?
Torbjoern Granlund; homepage: http://swox.se/~tg/ . From MAINTAINERS:
*synthetic multiply Torbjorn Granlund
--- Comment #10 from vda dot linux at googlemail dot com 2006-08-02 19:05
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Created an attachment (id=12000)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12000&action=view)
Alternative algorithm v. 2
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28417
--- Comment #9 from vda dot linux at googlemail dot com 2006-08-02 19:05
---
Thanks for the link to .pdf! Who's Tege? And his email address is ...?
Ok. This new version of the patch is working for signed divisions too, and is
giving the results which are always same or better than "old
--- Comment #8 from amylaar at gcc dot gnu dot org 2006-07-31 14:39 ---
(In reply to comment #3)
> Too bad there are no comments how the code works, what is mlow and mhigh.
Tege has written a paper: http://swox.se/~tg/divcnst-pldi94.pdf
Also, you might consider adding him to the CC lis
--- Comment #7 from vda dot linux at googlemail dot com 2006-07-30 13:43
---
Created an attachment (id=11973)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11973&action=view)
Random tester
Randomly chooses a/b and compares "gcc patch code" results with code which was
previously v
--- Comment #6 from vda dot linux at googlemail dot com 2006-07-30 13:38
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Patched versus stock gcc-4.1.1 on this code
unsigned v;
void f9188_mul365384439_shift27(unsigned A) { v = A/(unsigned)1577682821; }
is:
# diff -u suboptimal-411-O2.s suboptimal-411-O2-fixed.s
--- suboptimal-
--- Comment #5 from vda dot linux at googlemail dot com 2006-07-30 13:37
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Created an attachment (id=11972)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11972&action=view)
Test program
Compile with -O2 -S to see the assembly.
Compile with -Os and run to check the correctness.
--- Comment #4 from vda dot linux at googlemail dot com 2006-07-30 13:35
---
Created an attachment (id=11971)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11971&action=view)
Use alternative algorithm if it gives better results
New algorithm lives in separate function gcc_fastdiv
--- Comment #3 from vda dot linux at googlemail dot com 2006-07-19 16:24
---
I instrumented choose_multiplier(). When called like this:
choose_multiplier(d=1577682821,n=32,precision=32),
it returns *post_shift_ptr=31,multiplier=5846151023
whereas optimal one is *post_shift_ptr=27,multi
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