[FFmpeg-devel] [PATCH 1/3] Move lpc_compute_autocorr() from DSPContext to a new struct LPCContext.

[Michael Niedermayer]

On Fri, Jan 21, 2011 at 03:48:30AM +0000, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> 
> > On Fri, Jan 21, 2011 at 02:31:06AM +0000, M?ns Rullg?rd wrote:
> >> Luca Barbato <lu_zero at gentoo.org> writes:
> >> 
> >> > On 01/21/2011 02:03 AM, Michael Niedermayer wrote:
> >> >> Dont you think that the code that contains these offsets would
> >> >> benefit more from cleanup to not break when random structs change
> >> >> than regularly waiting for failure and then find someone with an
> >> >> ARM build env to fix?
> >> >
> >> > It had been discussed a bit in the past. There isn't a portable way to
> >> > get those offsets automatically given the field of use (arm is mostly
> >> > cross-built, more than often with exotic toolchain).
> >> 
> >> A different approach would be to group the handful of field into a
> >> sub-struct and pass a pointer to that instead of the MpegEncContext
> >> pointer.  However, given the general appearance of MpegEncContext,
> >> doing this can seem a bit scary.
> >
> > simply moving the affected fields close together and passing a
> > pointer to the first seems easiest,
> 
> This is also unreliable.  Consider this struct:
> 
> struct foo {
>     char a;
>     int  b;
> };
> 
> Here the offset from &a to &b is 4 (assuming a typical ABI).  Now add
> a member to the struct:
> 
> struct foo {
>     char x;
>     char a;
>     int  b;
> };
> 
> After this change the offset from &a to &b is 3.  MpegEncContext is
> full of padding holes, so effects like this are likely to arise with
> any modification.
> 
> I'm as keen as anyone to find a better solution, but going from one
> fragile method to another is pointless.

its not pointless its an improvment besides what i meant is
sort from field needing most alignment to least.

and btw, iam just helping because it was obvious when reading that and iam
too much a geek to not help in such cases i havnt forgotten what happened

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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