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

[Vitor Sessak]

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.

-Vitor
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