[Speex-dev] Problem with Blackfin assembly optimizations -- bug in fixed_bfin.h / resampler saturation???

[Jean-Marc Valin]

Frank Lorenz a écrit :
> Yes, this is another point: I wrote that the resampler breaks, but
> this is not the case. Instead, the speex encoder corrupts its input
> buffer when the "DIV32_16 bug" described above happens. Do you have
> any idea how to proceed?

Can you try enabling --enable-fixed-point-debug (FIXED_DEBUG) and see if
any error gets printed. I suspect there might be a place where the
assumptions of DIV32_16 are violated, i.e. either the right hand side
doesn't fit in 16 bits or the result doesn't fit in 16 bits. Can you check?

	Jean-Marc

> best regards, Frank
> 
> 
> -----Ursprüngliche Nachricht----- Von: "Jean-Marc Valin"
> <jean-marc.valin at usherbrooke.ca> Gesendet: 06.02.08 11:07:46 An:
> Frank Lorenz <Frank_wtal at web.de> CC: speex-dev at xiph.org Betreff: Re:
> [Speex-dev] Problem with Blackfin assembly optimizations -- bug in
> fixed_bfin.h / resampler saturation???
> 
> 
> Frank Lorenz a écrit :
>> I just started to examine the DIV32_16 function (Blackfin ASM 
>> version), and wondered why the return value of the function inside 
>> 'fixed_bfin.h' is of type 'spx_word16_t', but the local variable 
>> 'res' which is returned by this function is of type 'spx_word32_t'.
>>  Is this a trick of optimization or a bug? (Same question for 
>> PDIV32_16 and MAX16, too!)
> 
> Neither (AFAIK). The idea is that sometimes gcc does 
> silly/counter-intuitive things when I specify a 16-bit variable as a 
> constraint. That way, I force the top 16 bits to be zero.
> 
> Jean-Marc
> 
>> best regards, Frank
>> 
>> 
>> -----Ursprüngliche Nachricht----- Von: "Jean-Marc Valin" 
>> <jean-marc.valin at usherbrooke.ca> Gesendet: 02.02.08 06:26:08 An: 
>> speex-dev <speex-dev at xiph.org> Betreff: Re: FW: Re: [Speex-dev] 
>> Problem with Blackfin assembly optimizations -- bug in fixed_bfin.h
>> / resampler saturation???
>> 
>> 
>> Frank Lorenz a écrit :
>>> And yes, the same "overflow" happens even when I disable Blackfin
>>>  ASM optimizations.
>> Indeed, that shouldn't happen. Just to make sure I understand, so
>> far there's two problems: 1) DIV32_16() in Blackfin assembly causes
>>  problems 2) The resampler overflows
>> 
>> When you fix/workaround those two, is the encoder/decoder working 
>> correctly or are there other issues?
>> 
>> About the DIV32_16() issue, could you try and replace it with a 
>> function that compares the Blackfin-asm result with the real
>> division and dumps the args and output when they don't match. I'd
>> like to understand for what inputs that functions fails. That would
>> help in fixing the problem.
>> 
>> Thanks,
>> 
>> Jean-Marc
>> 
>>> best regards, Frank
>>> 
>>> -----Ursprüngliche Nachricht----- Von: "Jean-Marc Valin" 
>>> <jean-marc.valin at usherbrooke.ca> Gesendet: 01.02.08 12:11:39 An:
>>>  Frank Lorenz <Frank_wtal at web.de> CC: speex-dev at xiph.org Betreff:
>>>  Re: FW: Re: [Speex-dev] Problem with Blackfin assembly 
>>> optimizations -- bug in fixed_bfin.h / resampler saturation???
>>> 
>>> 
>>> Frank Lorenz a écrit :
>>>> didn't get a reply to my last post (see below) -- do you have
>>>> no idea what happens here?
>>> Sorry, been quite busy lately. Still have a backlog of things to
>>>  respond to (sorry to others as well), some of it quite old.
>>> 
>>>> After some more tests, I disabled the DIV32_16 Blackfin 
>>>> optimizations and now get good quality on the Blackfin.
>>> OK, I'll need to investigate that one. It's mostly taken from the
>>>  ADI manual, so I don't see what could have happened.
>>> 
>>>> But when I have overdrive on the input, things become very bad
>>> Does that happen without any assembly. Some amount of badness is
>>>  expected from the fixed-point because of saturation issues. It 
>>> shouldn't overflow though (can you check?)
>>> 
>>>> -- I'm not sure if this is really a filter stability issue like
>>>> I wrote some weeks ago.
>>> I don't think it has to do with filters.
>>> 
>>>> I use the speex resampler to downsample from 48 to 16 kHz. When
>>>> I look to the downsampled signal before passing it to the
>>>> encoder, there seems to be a bug in saturation. On overdrive,
>>>> instead of holding a too big signal value at maximum (e.g.
>>>> 32767) for some samples, the sample values I get from the
>>>> resampler are [-32768,32767,-32768,...], i.e. the output of the
>>>> resampler alters between the biggest possible negative value
>>>> and the biggest possible positive value.
>>> This is definitely bad. Can you send me an example file. Also,
>>> can you reproduce that problem without the Blackfin assembly?
>>> 
>>>> Does the resampler use the hardware saturation available on 
>>>> Blackfin, or does it saturate by software? Can you point me to 
>>>> the place I have to look at inside the resampler function for 
>>>> saturation?
>>> Saturation is entirely done in software. The resampler does the 
>>> conversion using the WORD2INT macro.
>>> 
>>> Jean-Marc
>>> 
>>> 
>>> 
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>> 
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> 
> 
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