[Speex-dev] Speex inner_prod()

[Jerry Trantow]

I am overriding the inner product routine in ltp.c.  To test my replacement,
I threw some test vectors at it.  I understand the loss of resolution caused
by the shift.  I also see a FIXED_POINT danger with the summation of four
mults overflowing the 32 bit before the shift.  

I can fix this by accumulating each term into a long, but if the code scales
the x[],y[] vectors to avoid this problem I could use parallel 16x16
multiply/adds.  

You can see this problem with the following test case.

for (i=0;i<40;i++)
{
	x[i]=-16384;
	y[i]=-32768;
}
sum0=inner_prod(x, y, 40);
fprintf(stderr,"inner_prod0(%8d).\n",sum0);


Jerry J. Trantow
Applied Signal Processing, Inc.
jtrantow at ieee.org