[FFmpeg-devel] [PATCH] Common ACELP code & G.729 [2/7] - pitch lag decoding

[Vladimir Voroshilov]

2008/6/27 Michael Niedermayer <michaelni at gmx.at>:
> On Fri, Jun 27, 2008 at 06:30:00AM +0700, Vladimir Voroshilov wrote:
>> 2008/6/27 Michael Niedermayer <michaelni at gmx.at>:
>> > On Fri, Jun 27, 2008 at 12:00:01AM +0700, Vladimir Voroshilov wrote:
>>
>> [...]
>>
>> >> +
>> >> +    for(i=0; i<ma_pred_order; i++)
>> >> +        energy += quant_energy[i] * ma_prediction_coeff[i];
>> >> +
>> >> +    innov_energy = sum_of_squares(fc_v, subframe_size, 0, 0);
>> >> +#ifdef G729_BITEXACT
>> >
>> >> +    energy +=  MULL(ff_log2(innov_energy), -24660) << 10;
>> >
>> > s/24660/6165/
>> > and i wonder if a normal * would do with the correctly simplified constant?
>>
>> Breaks bitexactness.
>
> you mean (x*2)>>1 != x then you have a overflow in your code

No, i meant ((x*2)>>2)<<1 != (x>>2)<<2
You didn't take in account MULL macro.
The reason is rounding, not overflow.

-- 
Regards,
Vladimir Voroshilov mailto:voroshil at gmail.com
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