[FFmpeg-devel] [PATCH 7/9] sbcenc: add MMX optimizations

[James Almer]

On 12/23/2017 5:44 PM, Aurelien Jacobs wrote:
> On Sat, Dec 23, 2017 at 03:35:28PM -0300, James Almer wrote:
>> On 12/23/2017 3:01 PM, Aurelien Jacobs wrote:
>>> This was originally based on libsbc, and was fully integrated into ffmpeg.
>>>
>>> Rough speed test:
>>> C version:    speed= 592x
>>> MMX version:  speed= 785x
>>> ---
>>>  libavcodec/sbcdsp.c          |   3 +
>>>  libavcodec/sbcdsp.h          |   2 +
>>>  libavcodec/x86/Makefile      |   2 +
>>>  libavcodec/x86/sbcdsp.asm    | 284 +++++++++++++++++++++++++++++++++++++++++++
>>>  libavcodec/x86/sbcdsp_init.c |  51 ++++++++
>>>  5 files changed, 342 insertions(+)
>>>  create mode 100644 libavcodec/x86/sbcdsp.asm
>>>  create mode 100644 libavcodec/x86/sbcdsp_init.c
>>
>> [...]
>>
>>> +;*******************************************************************
>>> +;void ff_sbc_calc_scalefactors(int32_t sb_sample_f[16][2][8],
>>> +;                              uint32_t scale_factor[2][8],
>>> +;                              int blocks, int channels, int subbands)
>>> +;*******************************************************************
>>> +INIT_MMX mmx
>>> +cglobal sbc_calc_scalefactors, 5, 7, 3, sb_sample_f, scale_factor, blocks, channels, subbands, ptr, blk
>>> +    ; subbands = 4 * subbands * channels
>>> +    shl  subbandsd, 2
>>> +    cmp  channelsd, 2
>>> +    jl   .loop_1
>>> +    shl  subbandsd, 1
>>> +
>>> +.loop_1:
>>> +    sub           subbandsq, 8
>>> +    lea           ptrq, [sb_sample_fq + subbandsq]
>>> +
>>> +    ; blk = (blocks - 1) * 64;
>>> +    lea           blkq, [blocksq - 1]
>>> +    shl           blkd, 6
>>> +
>>> +    movq          m0, [scale_mask]
>>
>> I insist, this can be easily loaded outside the loop. You have enough
>> spare regs to store a copy.
> 
> Oh, I forgot to reply to this. There isn't any register left available
> on x86_32, hence why I kept those load inside the loop.

You're not using a gprs to store the mask nor need to. You're using mmx
regs and have 5 left.