[FFmpeg-devel] [PATCH] do not hardcode filter order in ff_acelp_lspd2lpc()

[Vitor Sessak]

Michael Niedermayer wrote:
> On Sat, Nov 07, 2009 at 12:03:39AM +0100, Vitor Sessak wrote:
>> Michael Niedermayer wrote:
>>> On Thu, Nov 05, 2009 at 05:36:36AM +0100, Vitor Sessak wrote:
>>>> Reynaldo H. Verdejo Pinochet wrote:
>>>>> Hello Vitor
>>>>> Vitor Sessak wrote:
>>>>>> $subj. It is useful for SIPR but also it makes sense to make shared
>>>>>> functions as general as possible.
>>>>> QCELP part is ok but I'd make lp_half_order
>>>>> a single-byte sized type.
>>>> Fine for me (I suppose comparing uint8_t with int is not slower in any 
>>>> arch we support). New version attached.
>>>>
>>>> -Vitor
>>>>  lsp.c      |   12 ++++++------
>>>>  lsp.h      |    2 +-
>>>>  qcelpdec.c |    2 +-
>>>>  3 files changed, 8 insertions(+), 8 deletions(-)
>>>> 4c16615dbbd30c5ab006c8da8b879ea577097b39  lspd2lpc_2.diff
>>>> Index: libavcodec/lsp.c
>>>> ===================================================================
>>>> --- libavcodec/lsp.c	(revision 20450)
>>>> +++ libavcodec/lsp.c	(working copy)
>>>> @@ -155,20 +155,20 @@
>>>>      }
>>>>  }
>>>>  -void ff_acelp_lspd2lpc(const double *lsp, float *lpc)
>>>> +void ff_acelp_lspd2lpc(const double *lsp, float *lpc, uint8_t 
>>>> lp_half_order)
>>>>  {
>>>> -    double pa[6], qa[6];
>>>> +    double pa[lp_half_order+1], qa[lp_half_order+1];
>>>>      int   i;
>>>>  -    lsp2polyf(lsp,     pa, 5);
>>>> -    lsp2polyf(lsp + 1, qa, 5);
>>>> +    lsp2polyf(lsp,     pa, lp_half_order);
>>>> +    lsp2polyf(lsp + 1, qa, lp_half_order);
>>>>  -    for (i=4; i>=0; i--)
>>>> +    for (i=lp_half_order-1; i>=0; i--)
>>>>      {
>>>>          double paf = pa[i+1] + pa[i];
>>>>          double qaf = qa[i+1] - qa[i];
>>>>           lpc[i  ] = 0.5*(paf+qaf);
>>>> -        lpc[9-i] = 0.5*(paf-qaf);
>>>> +        lpc[(lp_half_order << 1) - 1 -i] = 0.5*(paf-qaf);
>>>>      }
>>> i would
>>> lpc2= lpc + (lp_half_order << 1) - 1;
>>> and
>>> lpc2[-i] = ...
>>> that way lp_half_order and i also become redundant and one can be droped
>>> about int8 vs. int, its possible that using int8 as index into an array
>>> like lpc[int8_variable] could be slower in some archs (x86 being one)
>> Since pa[] is an array not a pointer I cannot do the while(lp_half_order--) 
>> { (...) pa++; ga++; lpc++; lpc2--;} trick not to use the var "i" (and the 
>> other option would use lpc[int8_var]). In this new version I've also made 
>> the loop count forward to make it more readable.
> 
> you could change lp_half_order back to int if reynaldo doesnt mind.
> i think that would avoid the problem?

Yes, new patch attached.

-Vitor
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