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

[James Almer]

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.