From 16d4c28cbb9add358d4e6f30c412860638dc4f90 Mon Sep 17 00:00:00 2001 From: Ganesh Ajjanagadde Date: Wed, 25 Nov 2015 16:26:08 -0500 Subject: avcodec/mpegaudio_tablegen: speed up dynamic table creation 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 Signed-off-by: Ganesh Ajjanagadde --- 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 90c9de430a..9a9bb4d056 100644 --- a/libavcodec/mpegaudio_tablegen.c +++ b/libavcodec/mpegaudio_tablegen.c @@ -23,6 +23,7 @@ #include #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 86b2cd32b0..dd67a0977e 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]; -- cgit v1.2.3