Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: harder case for optimization |
| Date | 2014-11-28 00:46 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <m58d4p$o83$1@dont-email.me> (permalink) |
| References | <329933af-9991-4bb6-bb95-6c673cf3c72c@googlegroups.com> <WgNdw.13407$Qi7.8515@fx07.am4> |
On 27/11/14 23:07, BartC wrote:
> "fir" <profesor.fir@gmail.com> wrote in message
> news:329933af-9991-4bb6-bb95-6c673cf3c72c@googlegroups.com...
>
>> for each pixel of the screen (screen size not fixed. resizable in
>> runtime)
>> i calculate corresponding direction vector (this is absolute direction in
>> 3d space)
>>
>> //...A
>> for(int j=0; j<frame_size_y; j++)
>> {
>> //...B
>> for(int i=0; i<frame_size_x; i++)
>> {
>>
>> float3 dir;
>>
>> dir.x = head_x*i + ogon_x;
>> dir.y = head_y*i + ogon_y;
>> dir.z = head_z*i + ogon_z;
>
> So dir starts off (at i=0) as just (ogon.x, ogon.y, ogon.z).
>
> For each iteration, it will effectively add (head_x, head_y, head_z) to
> dir.
> So instead of the above, why not initialise dir in ...B. Then after the
> call
> to table_normalize(&dir), do:
>
> dir.x += head.x;
> dir.y += head.y;
> dir.z += head.z;
>
> which saves a multiply (actually, three multiplies).
>
Doing this transformation is risky - you will build up rounding errors,
and lose precision. Floating point does not work like "real" mathematics!
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 00:42 -0800
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-27 11:34 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-27 13:29 +0100
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-27 05:58 -0800
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-27 06:36 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 12:26 -0800
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-27 22:07 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 14:49 -0800
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 00:05 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 00:46 +0100
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 00:55 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 07:20 +0100
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 00:41 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 01:54 -0800
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 02:19 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 04:05 -0800
Closed captioning (Was: harder case for something or other) gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 12:15 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 06:11 -0800
Re: harder case for optimization gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 12:18 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 04:42 -0800
Re: harder case for optimization gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 16:37 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 08:48 -0800
Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-28 16:51 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 10:38 -0800
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 11:34 +0100
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 11:21 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 04:23 -0800
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 13:58 +0100
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 13:46 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 16:25 +0100
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 08:18 -0800
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:17 +0100
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 08:54 -0800
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:22 +0100
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 11:29 -0800
Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-28 19:51 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:58 +0100
Re: harder case for optimization Melzzzzz <mel@zzzzz.com> - 2014-11-28 21:03 +0100
Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-28 20:11 +0000
Re: harder case for optimization Melzzzzz <mel@zzzzz.com> - 2014-11-28 21:31 +0100
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 20:06 +0000
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 17:14 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:54 +0100
Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 20:16 +0000
Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 21:56 +0100
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 23:37 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 23:54 -0800
Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-28 11:01 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 23:52 -0800
Re: harder case for optimization Morris Dovey <mrdovey@iedu.com> - 2014-11-29 02:03 -0600
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 00:38 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 03:12 -0800
Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 12:09 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 04:18 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 05:22 -0800
Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 16:58 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 09:35 -0800
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-29 10:55 -0800
Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 21:00 +0000
Re: harder case for optimization Ian Collins <ian-news@hotmail.com> - 2014-11-30 11:25 +1300
Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 22:56 +0000
Re: harder case for optimization Ian Collins <ian-news@hotmail.com> - 2014-11-30 12:00 +1300
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 16:01 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 16:21 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 16:52 -0800
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 17:14 -0800
Re: harder case for optimization glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-11-30 00:20 +0000
Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-29 16:43 -0800
Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-29 17:29 +0000
Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-12-05 02:12 -0800
csiph-web