[FFmpeg-devel] [PATCH] Remove MULL macro from lsp.c

[Vladimir Voroshilov]

2008/8/26 Michael Niedermayer <michaelni at gmx.at>:
> On Tue, Aug 26, 2008 at 11:39:53AM +0700, Vladimir Voroshilov wrote:
>> 2008/8/26 Michael Niedermayer <michaelni at gmx.at>:
>> > On Mon, Aug 25, 2008 at 10:27:18PM +0700, Vladimir Voroshilov wrote:
>> >> 2008/8/25 Michael Niedermayer <michaelni at gmx.at>:
>> >> > On Sat, Aug 23, 2008 at 01:08:13AM +0700, Vladimir Voroshilov wrote:
>> >> >> Attached patch replaces MULL macro in lsp.c with multiplication and right shift.
>> >> >> Current code works wrong because one of macro's arguments is int16_t while asm
>> >> >> assumes both of them to be int.
>> >> >>
>> >> >> I'll also remove all occurences of MULL macro from my G.729 code.
>> >> >>
>> >> >> P.S. Another fix is leaving MULL there but explicitly cast the second
>> >> >> argument to (int).
>> >> >> I don't know which is better.
>> >> >
>> >> > I would say that the bug you are trying to fix is in MULL
>> >> > it should work when its arguments are not int.i
>> >>
>> >> i hope, somebody fix it then.
>> >>
>> >> >
>> >> > besides
>> >> >
>> >> > [...]
>> >> >>          f[i] = f[i-2];
>> >> >>          for(j=i; j>1; j--)
>> >> >> -            f[j] -= MULL(f[j-1], lsp[2*i-2]) - f[j-2]; // (3.22) * (0.15) * 2 -> (3.22)
>> >> >> +            f[j] -= (((int64_t)f[j-1] * lsp[2*i-2]) >> 14) - f[j-2]; // (3.22) * (0.15) * 2 -> (3.22)
>> >> >>
>> >> >
>> >> > please fix the comments
>> >>
>> >> I didn't see any error in it, though. If it looks confusing on not
>> >
>> > the comment says *2, there is nothing in the code that does *2
>>
>> code should be read as (2 * f * lsp) >> 15 which is equal to  f * lsp >> 14
>> "2*" removed due to optimization.
>
> when 2* is removed from the code it also has to be removed from the comment

I'll remove entire comment.

But i'm in doubt now.
What is better:
1. add (int) cast to MULL arguments in i386/mathops.h (as pengvado
suggest in IRC after discussing bug together with mru and
Dark_Shikari)
2. add (int) cast to MULL in my code
3. remove MULL from my code.

-- 
Regards,
Vladimir Voroshilov mailto:voroshil at gmail.com
JID: voroshil at gmail.com, voroshil at jabber.ru
ICQ: 95587719