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

[Måns Rullgård]

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.

-- 
M?ns Rullg?rd
mans at mansr.com