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authorGanesh Ajjanagadde <gajjanagadde@gmail.com>2015-11-27 20:15:42 -0500
committerGanesh Ajjanagadde <gajjanagadde@gmail.com>2015-12-01 19:05:19 -0500
commit1d0c94ddaef8225c75f72d5d8c54c34270f88d80 (patch)
tree472c0877fc14120c151de0ff019810dcba1f9f00
parent16d4c28cbb9add358d4e6f30c412860638dc4f90 (diff)
downloadffmpeg-1d0c94ddaef8225c75f72d5d8c54c34270f88d80.tar.gz
avcodec/mpegaudio_tablegen: more dynamic table creation speedups
This further speeds up runtime initialization, with identical generated tables. Sample benchmark (x86-64, Haswell, GNU/Linux): old: 34441423 decicycles in mpegaudio_tableinit, 8192 runs, 0 skips new: 10776291 decicycles in mpegaudio_tableinit, 8192 runs, 0 skips Most low hanging fruit is taken care of here. For some idea, note that 83,064 array elements totalling 233,722 bytes need to be initialized. Thus, with this patch, we average ~ 12.9 cycles per element or ~ 4.6 cycles per byte. Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
-rw-r--r--libavcodec/mpegaudio_tablegen.h22
1 files changed, 15 insertions, 7 deletions
diff --git a/libavcodec/mpegaudio_tablegen.h b/libavcodec/mpegaudio_tablegen.h
index dd67a0977e..1b273146cc 100644
--- a/libavcodec/mpegaudio_tablegen.h
+++ b/libavcodec/mpegaudio_tablegen.h
@@ -45,23 +45,28 @@ static float expval_table_float[512][16];
static av_cold void mpegaudio_tableinit(void)
{
int i, value, exponent;
- double exp2_lut[4] = {
+ static const 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];
+ static double pow43_lut[16];
+ double exp2_base = 2.11758236813575084767080625169910490512847900390625e-22; // 2^(-72)
+ double exp2_val;
+ double pow43_val = 0;
for (i = 0; i < 16; ++i)
- cbrt_lut[i] = cbrt(i);
+ pow43_lut[i] = i * cbrt(i);
for (i = 1; i < TABLE_4_3_SIZE; i++) {
- double value = i / 4;
double f, fm;
int e, m;
- f = value / IMDCT_SCALAR * cbrt(value) * exp2_lut[i & 3];
+ double value = i / 4;
+ if (i & 3 == 0)
+ pow43_val = value / IMDCT_SCALAR * cbrt(value);
+ f = pow43_val * exp2_lut[i & 3];
fm = frexp(f, &e);
- m = (uint32_t)(fm * (1LL << 31) + 0.5);
+ m = llrint(fm * (1LL << 31));
e += FRAC_BITS - 31 + 5 - 100;
/* normalized to FRAC_BITS */
@@ -69,8 +74,11 @@ static av_cold void mpegaudio_tableinit(void)
table_4_3_exp[i] = -e;
}
for (exponent = 0; exponent < 512; exponent++) {
+ if (exponent && exponent & 3 == 0)
+ exp2_base *= 2;
+ exp2_val = exp2_base * exp2_lut[exponent & 3] / IMDCT_SCALAR;
for (value = 0; value < 16; value++) {
- double f = value * cbrt_lut[value] * pow(2, (exponent - 400) * 0.25 + FRAC_BITS + 5) / IMDCT_SCALAR;
+ double f = pow43_lut[value] * exp2_val;
expval_table_fixed[exponent][value] = (f < 0xFFFFFFFF ? llrint(f) : 0xFFFFFFFF);
expval_table_float[exponent][value] = f;
}