From 1d0c94ddaef8225c75f72d5d8c54c34270f88d80 Mon Sep 17 00:00:00 2001 From: Ganesh Ajjanagadde Date: Fri, 27 Nov 2015 20:15:42 -0500 Subject: 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 Signed-off-by: Ganesh Ajjanagadde --- libavcodec/mpegaudio_tablegen.h | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) (limited to 'libavcodec/mpegaudio_tablegen.h') 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; } -- cgit v1.2.3