On Sat, Nov 28, 2015 at 12:03 PM, Ganesh Ajjanagadde <gajjanaga...@gmail.com> wrote: > This does some miscellaneous stuff mainly avoiding the usage of pow to > achieve significant speedups. This is not speed critical, but is > unnecessary latency and cycles wasted for a user. > > All tables tested and are identical to the old ones > (bit-exact even in floating point case). > > Sample benchmark (x86-64, Haswell, GNU/Linux): > old: > 102329530 decicycles in mpegaudio_tableinit, 1 runs, 0 skips > > new: > 34111900 decicycles in mpegaudio_tableinit, 1 runs, 0 skips > > Reviewed-by: Ronald S. Bultje <rsbul...@gmail.com> > Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> > --- > libavcodec/mpegaudio_tablegen.c | 1 + > libavcodec/mpegaudio_tablegen.h | 19 +++++++++++++------ > 2 files changed, 14 insertions(+), 6 deletions(-) > > diff --git a/libavcodec/mpegaudio_tablegen.c b/libavcodec/mpegaudio_tablegen.c > index 90c9de4..9a9bb4d 100644 > --- a/libavcodec/mpegaudio_tablegen.c > +++ b/libavcodec/mpegaudio_tablegen.c > @@ -23,6 +23,7 @@ > #include <stdlib.h> > #define CONFIG_HARDCODED_TABLES 0 > #include "mpegaudio_tablegen.h" > +#include "libavutil/tablegen.h" > #include "tableprint.h" > > int main(void) > diff --git a/libavcodec/mpegaudio_tablegen.h b/libavcodec/mpegaudio_tablegen.h > index 86b2cd3..dd67a09 100644 > --- a/libavcodec/mpegaudio_tablegen.h > +++ b/libavcodec/mpegaudio_tablegen.h > @@ -45,12 +45,21 @@ static float expval_table_float[512][16]; > static av_cold void mpegaudio_tableinit(void) > { > int i, value, exponent; > + double exp2_lut[4] = { > + 1.00000000000000000000, /* 2 ^ (0 * 0.25) */ > + 1.18920711500272106672, /* 2 ^ (1 * 0.25) */ > + M_SQRT2 , /* 2 ^ (2 * 0.25) */ > + 1.68179283050742908606, /* 2 ^ (3 * 0.25) */ > + }; > + double cbrt_lut[16]; > + for (i = 0; i < 16; ++i) > + cbrt_lut[i] = cbrt(i); > + > for (i = 1; i < TABLE_4_3_SIZE; i++) { > double value = i / 4; > double f, fm; > int e, m; > - /* cbrtf() isn't available on all systems, so we use powf(). */ > - f = value / IMDCT_SCALAR * pow(value, 1.0 / 3.0) * pow(2, (i & 3) * > 0.25); > + f = value / IMDCT_SCALAR * cbrt(value) * exp2_lut[i & 3]; > fm = frexp(f, &e); > m = (uint32_t)(fm * (1LL << 31) + 0.5); > e += FRAC_BITS - 31 + 5 - 100; > @@ -61,10 +70,8 @@ static av_cold void mpegaudio_tableinit(void) > } > for (exponent = 0; exponent < 512; exponent++) { > for (value = 0; value < 16; value++) { > - /* cbrtf() isn't available on all systems, so we use powf(). */ > - double f = (double)value * pow(value, 1.0 / 3.0) * pow(2, > (exponent - 400) * 0.25 + FRAC_BITS + 5) / IMDCT_SCALAR; > - /* llrint() isn't always available, so round and cast manually. > */ > - expval_table_fixed[exponent][value] = (long long int) (f < > 0xFFFFFFFF ? floor(f + 0.5) : 0xFFFFFFFF); > + double f = value * cbrt_lut[value] * pow(2, (exponent - 400) * > 0.25 + FRAC_BITS + 5) / IMDCT_SCALAR; > + expval_table_fixed[exponent][value] = (f < 0xFFFFFFFF ? > llrint(f) : 0xFFFFFFFF); > expval_table_float[exponent][value] = f; > } > exp_table_fixed[exponent] = expval_table_fixed[exponent][1]; > -- > 2.6.2 >
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