[FFmpeg-devel] [PATCH 3/3] ac3enc: add SIMD-optimized shifting functions for use with the fixed-point AC3 encoder

[Justin Ruggles]

On 03/08/2011 02:15 PM, Michael Niedermayer wrote:

> On Tue, Mar 08, 2011 at 01:59:44PM -0500, Ronald S. Bultje wrote:
>> Hi,
>>
>> On Tue, Mar 8, 2011 at 1:18 PM, Justin Ruggles <justin.ruggles at gmail.com> wrote:
>>> +%macro AC3_LSHIFT_INT16 1
>>> +cglobal ac3_lshift_int16_%1, 3,3,5, src, len, shift
>>> +    test   shiftd, shiftd
>>> +    jz .end
>>> +    movd       m0, shiftd
>>> +    ALIGN 8
>>> +.loop:
>>> +    AC3_SHIFT_4MM srcq, psllw, m0
>>> +    sub      lend, mmsize*2
>>> +    ja .loop
>>
>> If it's not a multiple of mmsize*2, this will loop forever. Making
>> this jg (= signed) would fix that.
> 
> really?
> i want that CPU on which ja behaves liek that


in testing, it did not cause an infinite loop.  i think because ja also
checks the carry flag?

-Justin