[FFmpeg-devel] [PATCH] AAC decoder
Michael Niedermayer
michaelni
Sun May 25 18:18:20 CEST 2008
On Sun, May 25, 2008 at 02:55:07PM +0100, Robert Swain wrote:
> 2008/5/24 Michael Niedermayer <michaelni at gmx.at>:
> > On Sat, May 24, 2008 at 06:35:37PM +0100, Robert Swain wrote:
> >> 2008/5/23 Michael Niedermayer <michaelni at gmx.at>:
> >> > On Fri, May 23, 2008 at 01:59:41PM +0100, Robert Swain wrote:
> >> >> Index: aac.c
> >> >> ===================================================================
> >> >> --- aac.c (revision 2185)
> >> >> +++ aac.c (working copy)
> >> >> @@ -366,7 +366,7 @@
> >> >> DECLARE_ALIGNED_16(float, sine_short_128[128]);
> >> >> DECLARE_ALIGNED_16(float, pow2sf_tab[256]);
> >> >> DECLARE_ALIGNED_16(float, intensity_tab[256]);
> >> >> - DECLARE_ALIGNED_16(float, ivquant_tab[256]);
> >> >> + DECLARE_ALIGNED_16(float, ivquant_tab[128]);
> >> >> MDCTContext mdct;
> >> >> MDCTContext mdct_small;
> >> >> MDCTContext *mdct_ltp;
> >> >> @@ -890,8 +890,11 @@
> >> >> // BIAS method instead needs values -1<x<1
> >> >> for (i = 0; i < 256; i++)
> >> >> ac->intensity_tab[i] = pow(0.5, (i - 100) / 4.);
> >> >> - for (i = 0; i < sizeof(ac->ivquant_tab)/sizeof(ac->ivquant_tab[0]); i++)
> >> >> - ac->ivquant_tab[i] = pow(i, 4./3);
> >> >> + for (i = 0; i < sizeof(ac->ivquant_tab)/(sizeof(ac->ivquant_tab[0])<<1); i++) {
> >> >> + int idx = i<<1;
> >> >> + ac->ivquant_tab[idx] = pow(i, 4./3);
> >> >> + ac->ivquant_tab[idx + 1] = -ac->ivquant_tab[idx];
> >> >> + }
> >> >>
> >> >> if(ac->dsp.float_to_int16 == ff_float_to_int16_c) {
> >> >> ac->add_bias = 385.0f;
> >> >
> >> >> @@ -1035,13 +1038,12 @@
> >> >> }
> >> >>
> >> >> static inline float ivquant(AACContext * ac, int a) {
> >> >
> >> >> - static const float sign[2] = { -1., 1. };
> >> >> int tmp = (a>>31);
> >> >> int abs_a = (a^tmp)-tmp;
> >> >> - if (abs_a < sizeof(ac->ivquant_tab)/sizeof(ac->ivquant_tab[0]))
> >> >> - return sign[tmp+1] * ac->ivquant_tab[abs_a];
> >> >> + if (abs_a < sizeof(ac->ivquant_tab)/(sizeof(ac->ivquant_tab[0])<<1))
> >> >> + return ac->ivquant_tab[(abs_a<<1) + !!tmp];
> >> >
> >> > ehh... this should be:
> >> >
> >> > if(a + 127U < 255U)
> >> > return ivquant_tab[a + 127U];
> >> >
> >> > (or other constants depending on what table size is best ...)
> >> >
> >> >
> >> >> else
> >> >> - return sign[tmp+1] * pow(abs_a, 4./3);
> >> >> + return (2 * tmp + 1) * pow(abs_a, 4./3);
> >> >
> >> > pow(fabs(a), 1./3) * a;
> >>
> >> With those suggestions it is much faster. The alternating sign
> >> construction for the table wasn't my idea, but I won't name names. :)
> >> Anyway, see attached. Benchmarks on the same FAAC encoded South Park
> >> episode:
> >>
> >> old size 256
> > [...]
> >> 3956 dezicycles in ivquant, 2096816 runs, 336 skipsup=0 drop=0
> >>
> >> new size 8
> > [...]
> >> 4840 dezicycles in ivquant, 2066668 runs, 30484 skips=0 drop=0
> >>
> >> new size 16
> > [...]
> >> 3650 dezicycles in ivquant, 2093424 runs, 3728 skipsp=0 drop=0
> >>
> >> new size 32
> > [...]
> >> 3438 dezicycles in ivquant, 2096888 runs, 264 skipsup=0 drop=0
> >>
> >> new size 64
> > [...]
> >> 3447 dezicycles in ivquant, 2096915 runs, 237 skipsup=0 drop=0
> >>
> >> new size 128
> > [...]
> >> 3431 dezicycles in ivquant, 2096918 runs, 234 skipsup=0 drop=0
> >>
> >> new size 256
> > [...]
> >> 3431 dezicycles in ivquant, 2096953 runs, 199 skipsup=0 drop=0
> >>
> >> new size 512
> > [...]
> >> 3438 dezicycles in ivquant, 2097093 runs, 59 skipsdup=0 drop=0
> >>
> >> It looks to me like there's little difference in performance when the
> >> table is of size 32 or larger. Should I use size 32?
> >
> > From the numbers i see, yes 32 seems the best choice.
> >
> > What bitrate did your test file have? High bitrate files might be faster
> > with larger tables, so if it was low bitrate then it might be worth retrying
> > with some higher bitrate.
>
> Same audio source but encoded to 320kbps with QuickTime.
> I included
> the full listings as some table sizes seem to behave strangely based
> on the number of calls.
Effects of the skipping of (some) pow() i assume ...
>
> size 32
[...]
> 16429 dezicycles in ivquant, 4169262 runs, 25042 skips drop=0
>
> size 64
[...]
> 11718 dezicycles in ivquant, 4147408 runs, 46896 skips drop=0
>
> size 128
[...]
> 7687 dezicycles in ivquant, 4148129 runs, 46175 skips0 drop=0
>
> size 256
[...]
> 5174 dezicycles in ivquant, 4166995 runs, 27309 skips0 drop=0
>
> size 512
[...]
> 3826 dezicycles in ivquant, 4183674 runs, 10630 skips0 drop=0
>
> size 1024
[...]
> 3250 dezicycles in ivquant, 4191225 runs, 3079 skips=0 drop=0
>
> size 2048
[...]
> 3109 dezicycles in ivquant, 4193283 runs, 1021 skips=0 drop=0
>From these numbers a table size of 1024 seems to be the lowest acceptable.
I guess the 4kb space wont matter compared to the speed loss a small table
would cause with such files.
>
> > [...]
> >> + for (i = 1; i < IVQUANT_SIZE/2; i++) {
> >> + ac->ivquant_tab[IVQUANT_SIZE/2 - 1 + i] = pow(i, 4./3);
> >> + ac->ivquant_tab[IVQUANT_SIZE/2 - 1 - i] = -ac->ivquant_tab[IVQUANT_SIZE/2 - 1 + i];
> >> + }
> >
> > cant that be simplified with pow(fabs(i), 1./3) * i as well?
>
> Done. I had some issues with unsigned + signed for the loop limits so
> I introduced IVQUANT_SIZE_U for the unsigned size and IVQUANT_SIZE_S
> for a signed version of the same. I don't know if this is the best
> approach but it seems OK to me. See attached.
>
> Rob
>
> PS - I love that quote...
>
> > Many that live deserve death. And some that die deserve life. Can you give
> > it to them? Then do not be too eager to deal out death in judgement. For
> > even the very wise cannot see all ends. -- Gandalf
> Index: aac.c
> ===================================================================
> --- aac.c (revision 2185)
> +++ aac.c (working copy)
> @@ -56,6 +56,9 @@
> #define MAX_CHANNELS 64
> #define MAX_TAGID 16
>
> +#define IVQUANT_SIZE_U 256U
> +#define IVQUANT_SIZE_S (int)IVQUANT_SIZE_U
I would prefer a IVQUANT_SIZE 256 and explicit (unsigned) casts where
needed
besides this, patch ok
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
I count him braver who overcomes his desires than him who conquers his
enemies for the hardest victory is over self. -- Aristotle
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