[FFmpeg-devel] [PATCH 2/2] ac3enc: add SIMD-optimized shifting functions for use with the fixed-point AC3 encoder.

[Ivan Kalvachev]

On 3/12/11, M?ns Rullg?rd <mans at mansr.com> wrote:
> Justin Ruggles <justin.ruggles at gmail.com> writes:
>
>> ---
>>  libavcodec/ac3dsp.c         |   24 +++++++++++++++++++++
>>  libavcodec/ac3dsp.h         |   22 +++++++++++++++++++
>>  libavcodec/ac3enc_fixed.c   |   40 ++---------------------------------
>>  libavcodec/x86/ac3dsp.asm   |   48
>> +++++++++++++++++++++++++++++++++++++++++++
>>  libavcodec/x86/ac3dsp_mmx.c |   12 ++++++++++
>>  5 files changed, 109 insertions(+), 37 deletions(-)
>>
>>
>> diff --git a/libavcodec/ac3dsp.c b/libavcodec/ac3dsp.c
>> index da3a123..83f48a6 100644
>> --- a/libavcodec/ac3dsp.c
>> +++ b/libavcodec/ac3dsp.c
>> @@ -50,10 +50,34 @@ static int ac3_max_msb_abs_int16_c(const int16_t *src,
>> int len)
>>      return v;
>>  }
>>
>> +static void ac3_lshift_int16_c(int16_t *src, unsigned int len,
>> +                               unsigned int shift)
>> +{
>> +    int i;
>> +
>> +    if (shift > 0) {
>> +        for (i = 0; i < len; i++)
>> +            src[i] <<= shift;
>> +    }
>> +}

You can shift 2 values at once if you read them as int32_t, shift and
then mask (masking could even be skipped if you are sure they will
never overflow).