[Ffmpeg-devel] [PATCH] flacenc - lpc and options

[Bobby Bingham]

> > +
> > +/**
> > + * Levinson-Durbin recursion.
> > + * Produces LPC coefficients from autocorrelation data.
> > + */
> > +static void compute_lpc_coefs(const double *autoc, int max_order,
> > +                              double lpc[][MAX_LPC_ORDER], double *ref)
> > +{
> > +   int i, j, i2;
> > +   double r, err, tmp;
> > +   double lpc_tmp[MAX_LPC_ORDER];
> > +
> > +   for(i=0; i<max_order; i++) lpc_tmp[i] = 0;
> > +   err = autoc[0];
> > +
> > +   for(i=0; i<max_order; i++) {
> > +      r = -autoc[i+1];
> > +      for(j=0; j<i; j++) {
> > +          r -= lpc_tmp[j] * autoc[i-j];
> > +      }
> > +      r /= err;
> > +      ref[i] = fabs(r);
> > +
> > +      err *= 1.0 - (r * r);
> > +
> > +      i2 = (i >> 1);
> > +      lpc_tmp[i] = r;
> > +      for(j=0; j<i2; j++) {
> > +         tmp = lpc_tmp[j];
> > +         lpc_tmp[j] += r * lpc_tmp[i-1-j];
> > +         lpc_tmp[i-1-j] += r * tmp;
> > +      }
> > +      if(i % 2) {
>
> i&1 is faster then i%2
>

Though if i was unsigned, gcc (4.1.1 at least - I'd hope other
versions too) is smart enough to generate the i&1 code in both cases.

-- 
Bobby Bingham