Re: [Discuss-gnuradio] Logarithmic algebra for FIR calculation?

[Eric Blossom]

On Tue, Jun 20, 2006 at 09:32:48AM -0700, Johnathan Corgan wrote:
> I was Googling around on constant modulus stuff and came across the 
> following paper:
> 
> http://www.ee.ucl.ac.uk/lcs/papers2002/LCS133.pdf

Thanks for the pointer.

> But it wasn't the CMA stuff that caught my attention, it was the 
> description of converting a transversal FIR filter from a MAC function 
> to an adder by going into the logarithmic domain, delay/adding the 
> (log)weights, then exponentiating. This appeared to be done with fixed 
> point integers. The log operation was approximated.
> 
> I'm not all that familiar with optimized floating point (it just works) 
> so I don't know how long SSE, etc. multiplies take, but I am interested 
> in knowing whether there is merit to this transform in time and MIPS for 
> a float based signal stream on a x86 processor such as we use in GNU Radio.

Floating point is very fast.  We can do pretty close to 1 MAC / clock cycle
on Pentium 3/4/M, Athlon and AMD-64.

> -Johnathan, posting from sunny, 109F Phoenix "but it's a dry heat" AZ :-(

Eric