diff options
| author | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-12-09 18:50:28 -0500 |
|---|---|---|
| committer | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-12-17 08:12:41 -0800 |
| commit | 07a8fbaa553205b496b68a62cb7bf7a968d0281b (patch) | |
| tree | b7fe0c3c8623dcb358c242c2066aded57ee352d0 /libavcodec/nellymoserenc.c | |
| parent | 39f8c7961dcd530e88d13c600145097106647d2e (diff) | |
lavc/nellymoserenc: avoid wasteful pow
exp2 suffices here. Some trivial speedup is done in addition here by
reusing results.
This retains accuracy, and in particular results in identical values
with GNU libm + gcc/clang.
sample benchmark (Haswell, GNU/Linux):
proposed : 424160 decicycles in pow_table, 512 runs, 0 skips
exp2 only: 1262093 decicycles in pow_table, 512 runs, 0 skips
old : 2849085 decicycles in pow_table, 512 runs, 0 skips
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Diffstat (limited to 'libavcodec/nellymoserenc.c')
| -rw-r--r-- | libavcodec/nellymoserenc.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/libavcodec/nellymoserenc.c b/libavcodec/nellymoserenc.c index d998dbafee..9d22ac8cca 100644 --- a/libavcodec/nellymoserenc.c +++ b/libavcodec/nellymoserenc.c @@ -179,8 +179,18 @@ static av_cold int encode_init(AVCodecContext *avctx) /* Generate overlap window */ ff_init_ff_sine_windows(7); + /* faster way of doing for (i = 0; i < POW_TABLE_SIZE; i++) - pow_table[i] = pow(2, -i / 2048.0 - 3.0 + POW_TABLE_OFFSET); + pow_table[i] = 2^(-i / 2048.0 - 3.0 + POW_TABLE_OFFSET); */ + pow_table[0] = 1; + pow_table[1024] = M_SQRT1_2; + for (i = 1; i < 513; i++) { + double tmp = exp2(-i / 2048.0); + pow_table[i] = tmp; + pow_table[1024-i] = M_SQRT1_2 / tmp; + pow_table[1024+i] = tmp * M_SQRT1_2; + pow_table[2048-i] = 0.5 / tmp; + } if (s->avctx->trellis) { s->opt = av_malloc(NELLY_BANDS * OPT_SIZE * sizeof(float )); |