[FFmpeg-devel] [PATCH/RFC] Remove triplication of compute_lpc_coefs() function

[Vitor Sessak]

Michael Niedermayer wrote:
> On Sun, Aug 31, 2008 at 05:08:26AM +0200, Vitor Sessak wrote:
>> Michael Niedermayer wrote:
>>> On Thu, Aug 28, 2008 at 02:28:50PM +0200, Vitor Sessak wrote:
>>>> Hi all.
>>>>
>>>> I've finally found a more or less clean way of doing $subj. 

[...]

> 
> for(i=0; i<max_order; i++) {
>     LPC_type r = -autoc[i+1];
>     LPC_type *lpc_last= lpc;
>     lpc += lpc_stride;
> 
>     if (normalize) {
>         for(j=0; j<i; j++)
>             r -= lpc_last[j] * autoc[i-j];
> 
>         r /= err;
>         err *= 1.0 - (r * r);
>     }
>     if (ref)
>         ref[i] = fabs(r);
> 
>     lpc[i] = r;
>     for(j=0; j < (i+1)>>1; j++) {
>         LPC_type f = lpc_last[    j];
>         LPC_type b = lpc_last[i-1-j];
>         lpc[    j] = f + r * b;
>         lpc[i-1-j] = b + r * f;
>     }
> 
>     if (fail && err < 0)
>         return -1;
> }

I like it, done.

> [...]
>> Index: libavcodec/lpc.h
>> ===================================================================
>> --- libavcodec/lpc.h	(revision 15050)
>> +++ libavcodec/lpc.h	(working copy)
>> @@ -45,4 +45,66 @@
>>                        int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
>>                        int omethod, int max_shift, int zero_shift);
>>  
>> +
>> +#ifdef LPC_USE_DOUBLE
>> +#define LPC_type double
>> +#else
>> +#define LPC_type float
>> +#endif
>> +
>> +/**
>> + * Levinson-Durbin recursion.
>> + * Produces LPC coefficients from autocorrelation data.
>> + */
>> +static inline int compute_lpc_coefs(const LPC_type *autoc,
>> +                                    int max_order,
>> +                                    LPC_type lpc[][MAX_LPC_ORDER],
>> +                                    LPC_type *ref,
>> +                                    LPC_type lpc_tmp[MAX_LPC_ORDER],
>> +                                    int fail, int normalize)
>> +{
>> +    int i, j;
>> +    LPC_type err = autoc[0];
>> +
>> +    if (fail && (autoc[max_order] == 0 || autoc[0] <= 0))
>> +        return -1;
>> +
>> +    for(i=0; i<max_order; i++) {
>> +        LPC_type r;
> 
>> +        if (normalize) {
>> +            r = -autoc[i+1];
>> +
>> +            for(j=0; j<i; j++)
>> +                r -= lpc_tmp[j] * autoc[i-j];
>> +
>> +            r /= err;
>> +        } else
> 
>> +            r = -autoc[i];
> 
> This can be factored out of the loop when autoc+1 is passed as argument
> instead of autoc for !normalize

I don't like it because I'll need to check autoc[-1] in the beginning...

>> +
>> +        if (ref)
>> +            ref[i] = fabs(r);
>> +
> 
>> +        err *= 1.0 - (r * r);
> 
> This line can be under if(normalize) above

done.

New version attached.

-Vitor
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