Re: [Linuxsampler-devel] Bear stepped on my right ear?

[<le...@gr...>]

Le 28 mai 04, =E0 15:28, Christian Schoenebeck a =E9crit :

> Es geschah am Donnerstag, 27. Mai 2004 23:36 als St=E9phane LETZ =
schrieb:
>> On 27 mai 04, at 23:08, be...@ga... wrote:
>>> The offending code (probably due to a cut'n paste error)
>>> is in line 199 of Voice.h
>>>
>>>  pOutputLeft[i++] +=3D this->FilterRight.Apply(&bq_base, &bq_main,
>>> effective_volume * ((((a * pos_fract) + b) * pos_fract + c) *
>>> pos_fract + x0));
>>>
>>> It should be
>>> pOutputRight[i++] +=3D ....
>>>
>>> Stephane spotted this problem and told me about it on IRC, he said
>>> tried a patch that speeds up things a bit
>>> (reading pSrc[0]..pSrc[7] in one rush in variables and then
>>> use these variable for the stereo cubic interpolator.
>>> He said on PPC its faster.
>>>
>>> Perhaps it makes sense to commit it ? Christian ?
>>> (I sent a copy of the diff to Christian).
>>
>> What really speedup is the use of float instead of double (3.0f=20
>> instead
>> of 3.0 and so on..) *if* computing in double is not required of=20
>> course.
>> But this must be tested on X86 before committing.
>
> What do you mean with "if" computing?


Using the 3 instead of explicit 3.0f  cause float to double conversion=20=

everywhere and consume some CPU. If double precision is not required,=20
then using float explicitely is better.



>
> The patch looks ok, except:
>
>              inline void InterpolateOneStep_Mono(sample_t* pSrc, int&=20=

> i,
> [snip]
> -                    float a   =3D (3 * (x0 - x1) - xm1 + x2) / 2;
> -                    float b   =3D 2 * x1 + xm1 - (5 * x0 + x2) / 2;
> -                    float c   =3D (x1 - xm1) / 2;
> +                    float a   =3D (3.0 * (x0 - x1) - xm1 + x2) * =
0.5f;
> +                    float b   =3D 2.0 * x1 + xm1 - (5.0 * x0 + x2) *=20=

> 0.5f;
> +                    float c   =3D (x1 - xm1) * 0.5f;
>
> Intended? Why not:
>
> +                    float a   =3D (3.0f * (x0 - x1) - xm1 + x2) * =
0.5f;
> +                    float b   =3D 2.0f * x1 + xm1 - (5.0f * x0 + x2) =
*=20
> 0.5f;
> +                    float c   =3D (x1 - xm1) * 0.5f;
>

A mistake.. Yes 2.0f  instead of 2.0.


> And the patch works of course for x86 and also fixes the 'only left=20
> channel'
> bug.
>
> CU
> Christian

Stephane