[Speex-dev] speex on TI C5x fixed-point DSP

[Jamey Hicks]

Jean-Marc Valin wrote:

>>One thing I've noticed so far in the filter_mem2 code is the calls to 
>>SATURATE(x, 805306368).  805306368 is 0x30000000.  I was expecting that 
>>to be on a bit boundary, say 0x3fffffff?  In which case the arithmetic 
>>saturation logic could be used.
>>    
>>
>
>I don't think it would make that big of a difference, since the
>saturation is outside of the inner loop. If it's that critical, you
>could probably remove the saturation completely and just make sure your
>signals are scaled properly (i.e. not too close to saturation).
>
>  
>
I just realized that.  I added counters for each of the arithmetic 
macros and discovered that mac16_32_q15 is the most frequent.  I'm not 
sure I can do much more without understanding the code better.  Q15 is 
Q1.15 format, right?  Looking at
  MAC16_32_Q15(long c, short a, long b)

Is b a Q15 represented as Q17.15 so that the implementation does not 
depend on saturating hardware?  If we do have saturating hardware, can I 
keep the b input saturated so that only 1 16x16->32 multiply is required 
instead of 2?  Essentially, pushing the saturation back into the inner 
loop because it's almost free.

Thanks,
Jamey