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

[Vitor Sessak]

M?ns Rullg?rd wrote:
> Diego Biurrun <diego at biurrun.de> writes:
> 
>> On Tue, Aug 05, 2008 at 06:24:32AM +0200, Vitor Sessak wrote:
>>> Michael Niedermayer wrote:
>>>> On Tue, Jul 29, 2008 at 08:20:45PM +0200, Vitor Sessak wrote:
>>>>> /**
>>>>>  * 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.
>> Would it be a problem for ra288 to use doubles?
> 
> Doubles are *really* slow on ARM Cortex-A8, so avoiding them is good.

Not only on ARM, but I imagine it will be slower in practically all 
archs due to worse cache usage.

-Vitor