[Speex-dev] Speex on TI C6x, Problem with TI C5x Patch

Jim Crichton jim.crichton at comcast.net
Thu May 26 05:17:57 PDT 2005


>> > It's odd that it "almost" works with the fixed_generic.h. The easiest
>> > thing would be to gradually replace routines and see which one causes
>> > problem. It's most likely (though I'm not 100% sure) that somewhere in
>> > the code, I have a 16-bit value that gets sent to a function/macro that
>> > expects a 32-bit value. In that case, Stuart's fixed_c55x.h file would
>> > work because the inline function would first force the conversion to 32
>> > bits. My initial guess would be with the SH[RL]32 and ADD32 functions.

Nice call.  The culprit is SHRL32.  This is not used in many places, and in 
most of those, the operand comes from EXTEND32.  The only really suspicious 
instances is in lsp.c (lsp_interpolate):

   spx_word16_t tmp = DIV32_16(SHL32(1 + subframe,14),nb_subframes); 
(subframe is an int)

> I just checked in changes that may fix some bad behavior on 16-bit
> architectures. You might want to try if it fixes the problem. As I said,
> it's not clear yet whether the problem is in fixed_generic.h or if it's
> somewhere else and Stuart's fixed_c55.h just happens to work around it.

I see that your changes include adding an EXTEND32 to the line above.  I 
made ONLY this change to the 1.1.8 base that I am working from, and the 
problem is gone.

I will go back to using fixed_generic.h for now, but it may still be 
worthwhile to make a custom version that takes advantage of the compiler 
intrinsics, which include 32-bit shifts, 16x16=32 and 32x16=32 MPY, and 
32+16x16=32 MAC (with and without rounding).  The multiply arithmetic all 
returns saturated results.  It seems to me that can't hurt.  Do you see any 
problem with using saturated MPY and MACs?

By the way, the lsp.c change also fixes the TI C54x build, as expected.

- Jim Crichton 

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