[FFmpeg-devel] [PATCH 3/3] lavc/wmadec: replace pow by faster functions

[Ganesh Ajjanagadde]

On Fri, Jan 22, 2016 at 4:45 PM, Paul B Mahol <onemda at gmail.com> wrote:
> On 1/22/16, Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
>> On Sat, Jan 16, 2016 at 12:31 AM, Ganesh Ajjanagadde
>> <gajjanagadde at gmail.com> wrote:
>>> Further speedups possible by getting rid of exp2f...
>>>
>>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>>> ---
>>>  libavcodec/wmadec.c | 5 +++--
>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/libavcodec/wmadec.c b/libavcodec/wmadec.c
>>> index da54182..1a84323 100644
>>> --- a/libavcodec/wmadec.c
>>> +++ b/libavcodec/wmadec.c
>>> @@ -35,6 +35,7 @@
>>>
>>>  #include "libavutil/attributes.h"
>>>  #include "libavutil/internal.h"
>>> +#include "libavutil/libm.h"
>>>
>>>  #include "avcodec.h"
>>>  #include "internal.h"
>>> @@ -164,7 +165,7 @@ static av_cold void
>>> wma_lsp_to_curve_init(WMACodecContext *s, int frame_len)
>>>      /* tables for x^-0.25 computation */
>>>      for (i = 0; i < 256; i++) {
>>>          e                     = i - 126;
>>> -        s->lsp_pow_e_table[i] = pow(2.0, e * -0.25);
>>> +        s->lsp_pow_e_table[i] = exp2f(e * -0.25);
>>>      }
>>>
>>>      /* NOTE: these two tables are needed to avoid two operations in
>>> @@ -173,7 +174,7 @@ static av_cold void
>>> wma_lsp_to_curve_init(WMACodecContext *s, int frame_len)
>>>      for (i = (1 << LSP_POW_BITS) - 1; i >= 0; i--) {
>>>          m                      = (1 << LSP_POW_BITS) + i;
>>>          a                      = (float) m * (0.5 / (1 << LSP_POW_BITS));
>>> -        a                      = pow(a, -0.25);
>>> +        a                      = 1/sqrt(sqrt(a));
>>>          s->lsp_pow_m_table1[i] = 2 * a - b;
>>>          s->lsp_pow_m_table2[i] = b - a;
>>>          b                      = a;
>>> --
>>> 2.7.0
>>>
>>
>> ping, note that second can be made sqrtf(sqrtf(x)) at some error which
>> I deliberately avoided here.
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>> ffmpeg-devel at ffmpeg.org
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>>
>
> ok, if fate passes.

set pushed, thanks