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Groups > comp.arch.embedded > #20090
| From | Dimiter_Popoff <dp@tgi-sci.com> |
|---|---|
| Newsgroups | comp.arch.embedded |
| Subject | Re: two fpu compared |
| Date | 2015-02-14 23:19 +0200 |
| Organization | TGI |
| Message-ID | <mboe3j$io$1@dont-email.me> (permalink) |
| References | <ck36l8Fak5nU1@mid.individual.net> <mbht2f$v21$1@dont-email.me> <ck6f5eF66ovU1@mid.individual.net> <mbnpm6$m03$1@speranza.aioe.org> |
On 14.2.2015 г. 17:30, glen herrmannsfeldt wrote: > alb <al.basili@gmail.com> wrote: > >> David Brown <david.brown@hesbynett.no> wrote: > >>>> assuming two differently implemented FPU, both validated against the >>>> IEEE754, and limiting operations to the golden 5 (+,-, *, /, sqr), can I >>>> be sure that provided the inputs operands are the same the result would >>>> be the same bit wise? > >>> It is normal to view floating point operations as slightly imprecise - >>> there is a rule that you never compare floating point data with ==. > > (snip) > >> the extra bit I got recently is that the result is converted to an >> integer of 11bit which, a priori, means that a lot of the low bit >> precision from the 32bit is anyhow lost. > > Are you sure the calculation should be done in floating point? > Without more details, I suspect it could be done in fixed point, > the results would not vary depending on implementations, and > everyone would be happy. Sometimes the choice to do something using an FPU is not because things cannot be done using the integer unit but just because one needs the horsepowers the FPU adds to the chip. Was the case with me on my netMCA-3 design - the FPU did make things a bit more complicated but using it was the only way to do what I did. Apart from the sheer ops per clock cycle it (being 64 bit of course, 32 bit FPU-s are pretty much useless) gave me the dynamic range I needed (32 bits integers would not have sufficed and multiprecision would have slowed things down beyond any practical usability). > (There is only one question left, and that is the way division > works when one operand is negative.) Why is that, what pitfalls do you envisage? "Normally" one would divide the absolute values and just xor the sign bits after that, you must have something else/more to it than that in mind. Dimiter ------------------------------------------------------ Dimiter Popoff, TGI http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/
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two fpu compared al.basili@gmail.com (alb) - 2015-02-12 08:30 +0000
Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-12 10:51 +0100
Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-13 14:14 +0000
Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-13 16:23 +0100
Re: two fpu compared Colin Paul de Gloucester <not_a_real_email@address.com> - 2015-02-13 17:37 +0100
Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-16 08:01 +0000
Re: two fpu compared Colin Paul de Gloucester <not_a_real_email@address.com> - 2015-02-16 11:43 +0100
Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-17 10:35 +0000
Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-17 12:18 +0100
Re: two fpu compared George Neuner <gneuner2@comcast.net> - 2015-02-17 09:26 -0500
Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-17 16:47 +0100
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-17 20:54 +0200
Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-16 07:58 +0000
Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-16 09:53 +0100
Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-16 09:47 +0000
Re: two fpu compared Richard Damon <Richard@Damon-Family.org> - 2015-02-16 08:27 -0500
Re: two fpu compared Nobody <nobody@nowhere.invalid> - 2015-02-23 00:13 +0000
Re: two fpu compared George Neuner <gneuner2@comcast.net> - 2015-02-13 18:43 -0500
Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-14 15:30 +0000
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-14 23:19 +0200
Re: two fpu compared Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-02-14 23:28 +0100
Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-15 14:33 +0000
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-17 20:53 +0200
Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-18 01:55 +0000
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-18 17:54 +0200
Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-18 16:52 +0000
Re: two fpu compared Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-02-18 18:12 +0100
Re: two fpu compared Robert Wessel <robertwessel2@yahoo.com> - 2015-02-18 18:02 -0600
Re: two fpu compared Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-02-19 09:42 +0200
Re: two fpu compared Robert Wessel <robertwessel2@yahoo.com> - 2015-02-19 11:04 -0600
Re: two fpu compared Reinhardt Behm <rbehm@hushmail.com> - 2015-02-19 23:26 +0800
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-18 19:18 +0200
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-19 02:28 +0200
Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-19 16:29 +0000
Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-21 16:07 +0200
Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-12 11:26 +0000
Re: two fpu compared "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2015-02-12 12:29 +0100
Re: two fpu compared Dennis <dennis@none.none> - 2015-02-12 09:45 -0600
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