archive: Re: SETI Re: High bandwidth digitizer, FFT's, and analyzer

Re: SETI Re: High bandwidth digitizer, FFT's, and analyzer

David Woolley ( david@djwhome.demon.co.uk )
Sun, 4 Oct 1998 15:16:10 +0100 (BST)

> Well, thanks for helping clear that up. Now I have a bandwidth limit for the
> FFT processing of a PC. Have your figures taken into account the vast
> improvement in speed from changing the real mode math to integer math (ala the

The code fragment I did the instruction count on used integer, not real
arithmetic. The only factor that would really vary would be the estimate
of the number of processor cycles per instruction - I assumed an average of
2, which would be very optimisitc for a 486, but I don't have the relevant
data for a Pentium.

One thing, though, is that a 100MHz system would probably need 64 bit
arithmetic, which might require multiple integer instructions.

> tremendous fractal graphics program Fractint)? I suspect that your
> calculations are done using real mode math, instead of integer mode.

Incidentally, the book was wrong on the number of multiplies needed; it
gives the correct figure in a formula, but the wrong figure in a table.
I think the specgrm is code has the minimum number for a 2 point butterfly.