Re: [FFmpeg-devel] [PATCHv3] checkasm/lpc: test compute_autocorr

[James Almer <jamrial@gmail.com>]

On 5/27/2024 4:15 PM, James Almer wrote:
> On 5/27/2024 4:10 PM, James Almer wrote:
>> On 5/27/2024 1:01 PM, Rémi Denis-Courmont wrote:
>>> ---
>>> Changes since v2:
>>> - Scale the error factor to length since this computes sums.
>>> - Check the last element from results.
>>> - Use fixed vector size for benchmarks.
>>>
>>> ---
>>>   tests/checkasm/lpc.c | 51 +++++++++++++++++++++++++++++++++++++++++---
>>>   1 file changed, 48 insertions(+), 3 deletions(-)
>>
>> checkasm: using random seed 883526087
>> checkasm: bench runs 1024 (1 << 10)
>> SSE2:
>>   - lpc.apply_welch_window_even [OK]
>>   - lpc.apply_welch_window_odd  [OK]
>> 8:  666.011902576448 -  665.600444506565 =  0.411458069884
>>     autocorr_8_sse2 (lpc.c:88)
>>   - lpc.compute_autocorr        [FAILED]
> 
> The following fixes it:
> 
>> diff --git a/libavcodec/x86/lpc_init.c b/libavcodec/x86/lpc_init.c
>> index f2fca53799..9f41639feb 100644
>> --- a/libavcodec/x86/lpc_init.c
>> +++ b/libavcodec/x86/lpc_init.c
>> @@ -99,6 +99,15 @@ static void lpc_compute_autocorr_sse2(const double 
>> *data, ptrdiff_t len, int lag
>>              );
>>          }
>>      }
>> +
>> +    if(j==lag){
>> +        double sum = 1.0;
>> +        for(int i=j-1; i<len; i+=2){
>> +            sum += data[i  ] * data[i-j  ]
>> +                 + data[i+1] * data[i-j+1];
>> +        }
>> +        autoc[j] = sum;
>> +    }
>>  }
>>
>>  #endif /* HAVE_SSE2_INLINE */
> 
> So the SSE2 version is effectively broken, and ideally should be ported 
> to nasm as it's fixed.

Actually, that only fixes setting the last value. There are still 
failures in random places using several different seeds.
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