[Speex-dev] Shift count warning messages

Fri Jan 25 05:59:37 PST 2008

Jean-Marc,

I dug into this further, and found that the warning occurred when PSHR32 had 
a shift greater than 15.

in fixed_generic.h, PSHR32 is defined as:

#define PSHR32(a,shift) (SHR32((a)+((1<<((shift))>>1)),shift))

For 16-bit compilers the "1" needs a cast:

#define PSHR32(a,shift) (SHR32((a)+((EXTEND32(1)<<((shift))>>1)),shift))

This change fixed the warning, and it did change the assembled code.  With 
the original file, the ((1<<((shift))>>1)) was optimized away.
Note that fixed_debug.h has the same problem.

- Jim

----- Original Message ----- 
From: "Jean-Marc Valin" <jean-marc.valin at usherbrooke.ca>
To: "Jim Crichton" <jim.crichton at comcast.net>
Cc: <speex-dev at xiph.org>; "Michael Jacobson" <Michael.Jacobson at ultratec.com>
Sent: Wednesday, January 23, 2008 12:16 PM
Subject: Re: [Speex-dev] Shift count warning messages

> Thanks Jim for looking into that, I was really starting to wonder what
> was going on. Let me know if you find a way to tell the compiler to stop
> complaining.
>
> Jean-Marc
>
> Jim Crichton a écrit :
>> I looked back at my old C55 EC build, and I had the same warning in
>> mdf.c which Mike found.  The assembly code did have a valid shift, and
>> this build did cancel echo.
>>
>> When I built with the SVN head, I saw the errors in kiss_fft.c also.
>> The assembly there also has valid shifts.
>>
>> So, I suspect that these warnings do not indicate a real problem.  It
>> might be interesting to break down the offending lines into a sequence
>> of simpler instructions, to see if the compiler can be placated in that
>> way.
>>
>> - Jim
>>
>> ----- Original Message ----- From: "Jean-Marc Valin"
>> <jean-marc.valin at usherbrooke.ca>
>> To: "Jim Crichton" <jim.crichton at comcast.net>
>> Cc: "Michael Jacobson" <Michael.Jacobson at ultratec.com>;
>> <speex-dev at xiph.org>
>> Sent: Tuesday, January 22, 2008 4:00 PM
>> Subject: Re: [Speex-dev] Shift count warning messages
>>
>>
>>> Jim Crichton a écrit :
>>>> I played briefly with the echo canceller on the C5509A back in May
>>>> 2006.  I got the same compiler warnings, and sent a message to the
>>>> list which included this:
>>>>
>>>> "I got several compiler warnings for "shift out of range" in mdf.c,
>>>> which I fixed by adding EXTEND32 to all of the SHL32s with 16 bit
>>>> operands (st->frame_size in 6 places, st->wtmp2 in 1 place)."
>>>
>>> Yes, I remember those and I'm pretty sure they're fixed now. I think the
>>> problem comes from other changes I made later on, but I can't understand
>>> what's wrong.
>>>
>>>> I sent a patch with some fixes later that month, but I have not built
>>>> the echo canceller since then (no room for it).  It is very likely
>>>> that you are seeing the same issue, and the fix should be the same
>>>> also.  The trickier problems are the ones that the compiler does not
>>>> find.  EXTEND32 is usually the cure there also.
>>>>
>>>> Now that I look at mdf.c, though, W is declares as spx_word32_t, so
>>>> there should not be a problem, unless spx_word32_t is being mapped to
>>>> 16-bits.  That should not happen if you compile with CONFIG_TI_C54X
>>>> defined.  This is odd.
>>>
>>> In both cases, what I'm seeing is that the code does a shift right by
>>> more than 16 bits. Is it possible that the C5x doesn't want to do that,
>>> even for 32-bit operands? It's either that or there's a build problem
>>> that causes the operands to be 16 bit instead of 32. This is indeed very
>>> odd. Can you investigate a bit and check what the types are on both
>>> sides of the shift?
>>>
>>> Cheers,
>>>
>>> Jean-Marc
>>>
>>>
>>>
>>>
>>>> - Jim
>>>>
>>>>
>>>> ----- Original Message ----- From: Michael Jacobson To: Jean-Marc
>>>> Valin Cc: speex-dev at xiph.org Sent: Tuesday, January 22, 2008 9:54 AM
>>>> Subject: Re: [Speex-dev] Shift count warning messages
>>>>
>>>>
>>>> yes, our DSP is 16 bit based, and if those bits of code aren't using
>>>> 32 bit variables then yes that is what the warnings would be.  Does
>>>> this mean that the preprocessor and echo canceller won't work as well
>>>> because of this?
>>>>
>>>> -Mike
>>>>
>>>>>>> Jean-Marc Valin <jean-marc.valin at usherbrooke.ca> 01/18/08 8:42
>>>>>>> PM >>>
>>>>
>>>> I think these warnings are due to your DSP being 16-bit and that bit
>>>> of code not being 16-bit safe (unlike the encoder and decoder). Can
>>>> you confirm?
>>>>
>>>> Jean-Marc
>>>>
>>>> Michael Jacobson a écrit :
>>>>> Hi, I'm using 1.2beta3 on a 5416 DSP
>>>>>
>>>>> I have been getting warning messages that say: "kiss_fft.c", line
>>>>> 142: warning: shift count is too large
>>>>>
>>>>>
>>>>> I've noticed this on the echo canceller and the preprocessor.  all
>>>>> pretty much related to these two lines of code:
>>>>>
>>>>> kiss_fft C_MUL4(scratch[0],Fout[m] , *tw1 );
>>>>>
>>>>> mdf.c st->wtmp2[i] =
>>>>> EXTRACT16(PSHR32(st->W[j*N+i],NORMALIZE_SCALEDOWN+16));
>>>>>
>>>>> Is there some kind of switch I was supposed to throw to not get
>>>>> these messages? if not-are they hurting anything?
>>>>>
>>>>> -Mike
>>>>>
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________ Speex-dev mailing
>>>>> list Speex-dev at xiph.org
>>>>> http://lists.xiph.org/mailman/listinfo/speex-dev
>>>>
>>>>
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