[Bluez-devel] sbc synthesis inconsistencies

[Bluez-devel] sbc synthesis inconsistencies

[Brad Midgley]

Guys,

Have any of you looked closely at this? It comes straight from the spec 
for a2dp on page 66:


	/* Build a 80 values vector U */
	for (i = 0; i <= 4; i++) {
		for (j = 0; j < 8; j++) {
			state->U[ch][i * 16 + j] = state->V[ch][i * 32 + j];
			state->U[ch][i * 16 + j + 8] = state->V[ch][i * 32 + j + 24];
		}
	}

But isn't this code only populating u[ch][0..63] and not through 79 like 
the comment suggests? So the u[ch][64..79] terms are always 0 right?

This isn't the only thing that looks wrong in the spec. We also have a 
sliding window of v[] values that moves 16 values in each pass. The 
vector is 160 elements long even though the code above never accesses 
anything beyond the 128th value!

It's amazing this stuff even works as poorly specified as it is :(

BTW, in our code it looks like sbc_synthesize_eight was multiplying 
sbc_proto_8_80 by -4 where it should be -8. I changed that in cvs.

Brad


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Re: [Bluez-devel] sbc synthesis inconsistencies

[Peter Wippich]

Hi,

outer loop goes from i=0 up to i=4 -> 5 times * 8 * 2 = 80

Ciao,

Peter

On Sat, 3 Sep 2005, Brad Midgley wrote:

> Guys,
>
> Have any of you looked closely at this? It comes straight from the spec
> for a2dp on page 66:
>
>
> 	/* Build a 80 values vector U */
> 	for (i = 0; i <= 4; i++) {
> 		for (j = 0; j < 8; j++) {
> 			state->U[ch][i * 16 + j] = state->V[ch][i * 32 + j];
> 			state->U[ch][i * 16 + j + 8] = state->V[ch][i * 32 + j + 24];
> 		}
> 	}
>
> But isn't this code only populating u[ch][0..63] and not through 79 like
> the comment suggests? So the u[ch][64..79] terms are always 0 right?
>
> This isn't the only thing that looks wrong in the spec. We also have a
> sliding window of v[] values that moves 16 values in each pass. The
> vector is 160 elements long even though the code above never accesses
> anything beyond the 128th value!
>
> It's amazing this stuff even works as poorly specified as it is :(
>
> BTW, in our code it looks like sbc_synthesize_eight was multiplying
> sbc_proto_8_80 by -4 where it should be -8. I changed that in cvs.
>
> Brad
>
>
> -------------------------------------------------------
> SF.Net email is Sponsored by the Better Software Conference & EXPO
> September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
> Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
> Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
> _______________________________________________
> Bluez-devel mailing list
> Bluez-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/bluez-devel
>

|	Peter Wippich 			Voice: +49 30 46776411		|
|	G&W Instruments GmbH		fax:   +49 30 46776419		|
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|	D-13355 Berlin  / Germany					|




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Re: [Bluez-devel] sbc synthesis inconsistencies

[Brad Midgley]

Peter

> outer loop goes from i=0 up to i=4 -> 5 times * 8 * 2 = 80

Yes, thanks... I missed the <= (working too late).

I also remembered that Henryk was always testing the decoder against sbc 
files on the filesystem which simplifies testing. I'm going to have 
another whack at the simplification step and then try unrolling things.

Brad


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September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
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