Re: jpeg viewers

[dempson@actrix.gen.nz (David Empson)]

<pubpc1@library.ucla.edu> wrote:

> The 15MHz 65C816, although fast, is still lacking an FPU.  I noticed
> that when comparing a 13.75MHz '816 in a GS against a 25MHz '486 in
> a PC, in word processing and page layout applications, the GS is
> faster.  In graphics manipulation and spreadsheets, the GS falls
> behind.  The FPU in the '486 is a tremendous advantage in such tasks.

The FPU is not used in most simple graphical operations.  It is used
extensively in tasks like 3-D and rendering.

> The way someone once explained it to me is this.  For a CPU chip
> without an FPU to do, for example, division, it has to break everything
> down into addition and subtraction operations.  In other words, it
> must do long division (subtract, bring down the remainder, and repeat
> at the next decimal place) like a human being would do with pencil
> and paper.  With an FPU, the CPU is freed from doing this.  Thus,
> what would take many operations now takes only one.

Right, but it isn't associated with the FPU - just the main CPU's
ability to do integer multiply and divide operations.  The FPU also has
its own floating point multiplication and division support.

The 65816 has no multiply or divide instructions.  The 68000 and 8086
(plus all derivatives of each) have integer multiply and divide built
in.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand