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| From | MitchAlsup <MitchAlsup@aol.com> |
|---|---|
| Newsgroups | comp.arch |
| Subject | Re: Indirect Bit |
| Date | 2012-04-19 11:29 -0700 |
| Organization | http://groups.google.com |
| Message-ID | <16603280.18.1334860198726.JavaMail.geo-discussion-forums@ynnf1> (permalink) |
| References | <4F84FB1E.6CD1FC88@sonic.net> <1454560.470.1334600502251.JavaMail.geo-discussion-forums@ynbi17> <jmhor8$7pi$1@needham.csi.cam.ac.uk> <b992445b-d51c-4c5b-acb2-2ffcd5b4e7db@t7g2000pbp.googlegroups.com> <jmon4p$u8k$1@needham.csi.cam.ac.uk> |
On Thursday, April 19, 2012 4:50:17 AM UTC-5, nm...@cam.ac.uk wrote:
> >Certain floating-point optimizations are legitimate; others are not,
> >because they would result in massive loss of precision under some
> >circumstances. In general, compiler writers do know which is which,
> >and only perform legitimate optimizations when working with floating-
> >point.
>
> Absolutely NOT! Mitch has pointed out some of the issues, but the
> problem is well-known to be insoluble in theory and practice; the
> compiler is almost the worst place to make such decisions.
For todays lesson in FP optimizations: consider the following::
x = 3.0/7.0
if( x == 3.0/7.0 ) blah();
A) Is it legal for the optimizer to compute the 3.0/7.0 for the
assignment statement at compile time?
B) is it legal for the optimizer to compile the 3.0/7.0 for the
if-statement at compile time?
C) is it legal for the optimizer to dead-code-eliminate the if-
statement leaving only the call to blah() ?
{Leaving out the falacy of EVER comparing FP numbers for exactness}
Answers:
A) yes
B) no
C) no
This snippet of code is designed to determine if arithmetic operations
are carried out with more precision in registers than is store in memory.
For machines that have more precision in regsiters than in memory, blah
is never called.
Mitch
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Indirect Bit Mark Thorson <nospam@sonic.net> - 2012-04-10 19:31 -0800
Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-11 01:29 -0500
Re: Indirect Bit sarr.blumson@alum.dartmouth.org - 2012-04-11 14:48 +0000
Re: Indirect Bit mac <acolvin@efunct.com> - 2012-04-12 14:43 +0000
Re: Indirect Bit Morten Reistad <first@last.name> - 2012-04-22 15:19 +0200
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-22 23:24 -0700
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-11 08:32 +0200
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-11 05:49 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:22 -0700
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-13 08:14 -0700
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-13 16:13 -0700
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-13 20:01 -0700
Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-14 03:16 +0000
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-14 08:14 -0700
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-13 16:05 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-13 17:01 -0700
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-14 13:49 -0700
Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-13 20:07 -0400
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-14 18:47 +0200
Re: Indirect Bit Morten Reistad <first@last.name> - 2012-04-22 15:26 +0200
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-22 23:25 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 09:18 +0100
Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-23 19:35 -0400
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 08:37 +0100
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 09:42 +0100
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 01:58 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 11:26 +0100
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 05:02 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 13:58 +0100
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 10:07 -0700
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 04:30 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 13:01 +0100
Re: Indirect Bit Stefan Monnier <monnier@iro.umontreal.ca> - 2012-04-11 10:03 -0400
Re: Indirect Bit kenney@cix.compulink.co.uk - 2012-04-11 09:22 -0500
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-12 14:11 -0700
Re: Indirect Bit Stefan Monnier <monnier@iro.umontreal.ca> - 2012-04-12 18:05 -0400
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 20:13 -0700
Re: Indirect Bit Mark Thorson <nospam@sonic.net> - 2012-04-12 16:55 -0800
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-12 17:25 -0700
Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-12 20:03 -0500
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:33 -0700
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-13 15:57 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-13 17:03 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 20:14 -0700
Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-11 10:35 -0400
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-11 08:54 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 07:55 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-12 10:16 -0700
Re: Indirect Bit jacko <jackokring@gmail.com> - 2012-04-12 11:07 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:34 -0700
Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-12 11:35 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:41 -0700
Re: Indirect Bit jacko <jackokring@gmail.com> - 2012-04-13 14:52 -0700
Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-15 09:24 -0700
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-15 22:45 +0200
Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-15 18:04 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:12 -0700
Re: Indirect Bit timcaffrey@aol.com (Tim McCaffrey) - 2012-04-12 19:23 +0000
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-13 08:54 +0200
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-14 14:37 -0700
Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-15 23:42 +0000
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-16 08:08 -0700
Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-16 23:38 +0000
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-16 21:29 -0700
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-16 21:25 -0700
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-12 14:05 -0700
Re: Indirect Bit ChrisQ <blackhole@devnull.com> - 2012-04-14 10:12 +0000
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-14 06:25 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-14 14:50 +0100
Re: Indirect Bit ChrisQ <blackhole@devnull.com> - 2012-04-14 18:01 +0000
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-14 14:00 -0700
Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-14 20:58 -0400
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-16 09:57 -0700
Re: Indirect Bit timcaffrey@aol.com (Tim McCaffrey) - 2012-04-20 23:19 +0000
Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-16 08:50 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-16 18:09 +0100
Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-16 23:19 +0000
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-17 09:20 +0100
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-17 12:49 +0200
Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-17 12:40 +0000
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-18 12:01 +0100
Re: Indirect Bit anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-04-17 12:34 +0000
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-17 09:10 -0700
Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-17 22:05 +0000
Re: Indirect Bit jgk@panix.com (Joe keane) - 2012-04-19 19:37 +0000
Re: Indirect Bit torbenm@diku.dk (Torben Ægidius Mogensen) - 2012-04-20 11:10 +0200
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-20 11:24 +0200
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-20 15:01 +0100
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-20 15:03 +0100
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-20 08:01 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-20 16:35 +0100
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-18 11:10 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-18 15:37 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-16 11:21 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-16 19:36 +0100
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-18 11:17 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-18 15:33 -0700
Re: Indirect Bit Andreas Eder <andreas_eder@gmx.net> - 2012-04-19 00:29 +0200
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-19 10:50 +0100
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-19 11:29 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-19 21:39 +0100
Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-20 15:14 -0400
Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-20 22:43 -0700
Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-21 17:14 -0400
Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-21 19:47 -0500
Re: Indirect Bit Nomen Nescio <nobody@dizum.com> - 2012-04-22 10:45 +0200
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 09:57 +0100
Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-22 12:54 +0200
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 13:00 +0100
Re: Indirect Bit Nomen Nescio <nobody@dizum.com> - 2012-04-22 13:28 +0200
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 13:04 +0100
Re: Indirect Bit Fritz Wuehler <fritz@spamexpire-201204.rodent.frell.theremailer.net> - 2012-04-22 23:00 +0200
Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-22 18:05 -0400
Re: Indirect Bit glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-04-22 23:20 +0000
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 08:22 +0100
Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-22 03:56 -0700
Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-22 12:28 -0400
Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-22 12:56 -0500
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-22 13:15 -0700
Re: Indirect Bit Nomen Nescio <nobody@dizum.com> - 2012-04-22 22:30 +0200
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 21:40 +0100
Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-22 17:15 -0500
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 08:26 +0100
Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-23 08:02 -0700
Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 17:02 +0100
Re: Indirect Bit Fritz Wuehler <fritz@spamexpire-201204.rodent.frell.theremailer.net> - 2012-04-23 20:17 +0200
Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-23 13:07 -0500
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-22 13:16 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-23 13:14 -0700
Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-23 16:51 -0400
Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-23 14:22 -0700
Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-21 11:17 -0700
Re: Indirect Bit jacko <jackokring@gmail.com> - 2012-04-14 08:02 -0700
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