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

[Vitor Sessak]

Michael Niedermayer wrote:
> On Mon, Sep 01, 2008 at 07:03:23AM +0200, Vitor Sessak wrote:
>> 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. 
> [...]
>>> [...]
>>>> 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...
> 
> i meant autoc-1
> and there is no check for the !normalize case so no change to it because
> fail implicates normalize

I thought about that too, but I do not like to pass to functions a 
pointer to unallocated memory. I found it more ugly than my additional 
check.

-Vitor