On Wed, Mar 09, 2016 at 07:32:29PM +0100, Reimar Döffinger wrote: > On Wed, Mar 09, 2016 at 01:13:58PM +0100, Michael Niedermayer wrote: > > On Tue, Mar 08, 2016 at 10:16:50PM -0500, Ganesh Ajjanagadde wrote: > > > Yields 2x improvement in function performance, and boosts aac encoding > > > speed by ~ 4% overall. Sample benchmark (Haswell+GCC under -march=native): > > > after: > > > ffmpeg -i sin.flac -acodec aac -y sin_new.aac 5.22s user 0.03s system > > > 105% cpu 4.970 total > > > > > > before: > > > ffmpeg -i sin.flac -acodec aac -y sin_new.aac 5.40s user 0.05s system > > > 105% cpu 5.162 total > > > > > > Big shame that len-1 is -1 mod 4; 0 mod 4 would have yielded a further 2x > > > through > > > additional symmetry. Of course, one could approximate with the 0 mod 4 > > > variant, > > > error would essentially be ~ 1/len in the worst case. > > > > > > Signed-off-by: Ganesh Ajjanagadde <gajja...@gmail.com> > > > --- > > > libavcodec/lpc.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/libavcodec/lpc.c b/libavcodec/lpc.c > > > index 3839119..052aeaa 100644 > > > --- a/libavcodec/lpc.c > > > +++ b/libavcodec/lpc.c > > > @@ -176,9 +176,10 @@ double ff_lpc_calc_ref_coefs_f(LPCContext *s, const > > > float *samples, int len, > > > const double a = 0.5f, b = 1.0f - a; > > > > > > /* Apply windowing */ > > > - for (i = 0; i < len; i++) { > > > + for (i = 0; i <= len / 2; i++) { > > > > > double weight = a - b*cos((2*M_PI*i)/(len - 1)); > > > > the windows should not be recalcuated for each frame. But either > > calculated once during init or calculated at first use if that makes > > sense > > > > actually i suspect there should be close to 0 calls to libc math > > functions after init in the encoder, or is there some use of these > > functions in aac that cannot be replaced by a simple table? > > I don't understand the code, but I assumed that len changes > regularly here, which is the main problem. > I never actually checked if there is maybe only a small > number of common values at least though.
encoding matrixbench with defaults i get this list of lens with their freuqncies 1 ff_lpc_calc_ref_coefs_f 108 131 ff_lpc_calc_ref_coefs_f 116 148 ff_lpc_calc_ref_coefs_f 584 75 ff_lpc_calc_ref_coefs_f 84 1 ff_lpc_calc_ref_coefs_f 88 [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB I know you won't believe me, but the highest form of Human Excellence is to question oneself and others. -- Socrates
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