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| From | jacob navia <jacob@spamsink.net> |
|---|---|
| Newsgroups | comp.std.c |
| Subject | Re: Structure Packing. |
| Date | 2012-06-07 11:14 +0200 |
| Organization | lccwin |
| Message-ID | <jqprdl$cpk$1@speranza.aioe.org> (permalink) |
| References | <12b3df42-f6a0-4411-a5e5-136900f8255b@googlegroups.com> <lny5nzdhts.fsf@nuthaus.mib.org> |
Le 07/06/12 03:35, Keith Thompson a écrit :
> Given that the two members are of the same type, it's very likely that
> there will be no padding between them
Not true, for instance for the x86 with
struct s{
double var1;
double var2;
};
A compiler may align var2 to be 16 bytes after var1 so that accesses are
always at a 16 byte boundary for performance reasons. The xmm registers
(where all double data is stored in modern implementations) have a
faster "aligned" access to double data instruction.
It can be argued that the comiler could store var1 and var2 in a single
16 byte sequence so that they could be loaded into a single xmm register
but maybe for internal code generation reasons that would be not desired
(risk of polluting the high/low part, etc, necessity of
complex analysis to determine that the lower part and the higher part
aren't destroyed by some operation, etc).
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Structure Packing. John Kearney <dethrophes@googlemail.com> - 2012-06-06 17:27 -0700
Re: Structure Packing. James Kuyper <jameskuyper@verizon.net> - 2012-06-06 21:19 -0400
Re: Structure Packing. Walter Banks <walter@bytecraft.com> - 2012-06-11 22:39 -0400
Re: Structure Packing. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-12 09:21 -0400
Re: Structure Packing. Walter Banks <walter@bytecraft.com> - 2012-06-12 11:51 -0400
Re: Structure Packing. Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-06-12 18:37 +0200
Re: Structure Packing. Walter Banks <walter@bytecraft.com> - 2012-06-12 15:06 -0400
Re: Structure Packing. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-12 16:22 -0400
Re: Structure Packing. Walter Banks <walter@bytecraft.com> - 2012-06-12 17:44 -0400
Re: Structure Packing. Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-06-13 15:53 +0200
Re: Structure Packing. Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-06-18 12:37 +0300
Re: Structure Packing. Martin Shobe <martin.shobe@yahoo.com> - 2012-06-12 16:22 +0000
Re: Structure Packing. Walter Banks <walter@bytecraft.com> - 2012-06-12 15:24 -0400
Re: Structure Packing. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-12 16:33 -0400
Re: Structure Packing. Walter Banks <walter@bytecraft.com> - 2012-06-12 17:17 -0400
Re: Structure Packing. Keith Thompson <kst-u@mib.org> - 2012-06-06 18:35 -0700
Re: Structure Packing. John Kearney <dethrophes@googlemail.com> - 2012-06-06 21:58 -0700
Re: Structure Packing. Keith Thompson <kst-u@mib.org> - 2012-06-06 23:54 -0700
Re: Structure Packing. John Kearney <dethrophes@googlemail.com> - 2012-06-07 07:47 -0700
Re: Structure Packing. James Kuyper <jameskuyper@verizon.net> - 2012-06-07 12:39 -0400
Re: Structure Packing. jacob navia <jacob@spamsink.net> - 2012-06-07 11:14 +0200
Re: Structure Packing. Keith Thompson <kst-u@mib.org> - 2012-06-07 09:46 -0700
Re: Structure Packing. John Kearney <dethrophes@googlemail.com> - 2012-06-07 11:57 -0700
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