[FFmpeg-devel] [PATCH] update doc/optimization.txt

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> On Wed, Sep 22, 2010 at 02:11:49PM +0100, M?ns Rullg?rd wrote:
>> Michael Niedermayer <michaelni at gmx.at> writes:
>> 
>> > On Wed, Sep 22, 2010 at 08:37:07AM -0400, Ronald S. Bultje wrote:
>> >> Also, should I mention (in general tips) that functions that use huge
>> >> structs (e.g. MpegEncContext) are A) "discouragable" in general and B)
>> >> better written in inline asm than yasm because of the difficulty of
>> >> predicting struct offsets?
>> >
>> > B is ok about A, who uses huge structs when its not needed ...
>> 
>> If possible, the asm functions should be passed pointers into (or
>> values from) the struct in preference over passing a pointer to the
>> whole struct.
>
> if one needs just 1 pointer into a struct yes, if one needs 5, its not
> efficient to use up 5 registers and waste the time to initialize them
> besides that x86-32 has too few registers for this to work out

In many such cases, those values could be put in a struct of their own
contained within the larger struct.  Manually managing offsets in a
small struct is simple enough.

-- 
M?ns Rullg?rd
mans at mansr.com