[FFmpeg-devel] Review request - ra288.{c,h} ra144.{c,h}

[Justin Ruggles]

Vitor Sessak wrote:
> Michael Niedermayer wrote:
>> On Tue, Jul 29, 2008 at 08:20:45PM +0200, Vitor Sessak wrote:
>>> Hi,
>>>
>>> Those four files never passed a review. I've just finished cleaning them 
>>> up, so if anyone wants to review them (Michael already said he will), 
>>> now is time.
>> heres 288
>>
>> [...]
>>> static void decode(RA288Context *ractx, float gain, int cb_coef)
> 
> [...]
> 
>>> /**
>>>  * Converts autocorrelation coefficients to LPC coefficients using the
>>>  * Levinson-Durbin algorithm. See blocks 37 and 50 of the G.728 specification.
>>>  *
>>>  * @return 0 if success, -1 if fail
>>>  */
>>> static int eval_lpc_coeffs(const float *in, float *tgt, int n)
>>> {
>>>     int i, j;
>>>     double f0, f1, f2;
>>>
>>>     if (in[n] == 0)
>>>         return -1;
>>>
>>>     if ((f0 = *in) <= 0)
>>>         return -1;
>>>
>>>     in--; // To avoid a -1 subtraction in the inner loop
>>>
>>>     for (i=1; i <= n; i++) {
>>>         f1 = in[i+1];
>>>
>>>         for (j=0; j < i - 1; j++)
>>>             f1 += in[i-j]*tgt[j];
>>>
>>>         tgt[i-1] = f2 = -f1/f0;
>>>         for (j=0; j < i >> 1; j++) {
>>>             float temp = tgt[j] + tgt[i-j-2]*f2;
>>>             tgt[i-j-2] += tgt[j]*f2;
>>>             tgt[j] = temp;
>>>         }
>>>         if ((f0 += f1*f2) < 0)
>>>             return -1;
>>>     }
>>>
>>>     return 0;
>>> }
>> duplicate of compute_lpc_coefs() ?
> 
> Yes, the two functions are practically identical, but 
> compute_lpc_coefs() use doubles and ra288 uses floats.
> 
> Justin: does FLAC really need double precision or that was just an 
> arbitrary choice?

I know I ran some compression comparison tests at one point, and using
floats vs. doubles did negatively affect compression.  How much, I don't
remember.  I'll test again and post the results.  If it's not too bad,
I'm ok with changing to floats.

-Justin