On 2006-12-21, at 23:42, Robert Dewar wrote:
Marcin Dalecki wrote:
Of course I didn't think about a substitute for ==. Not! However I
think
that checks for |x-y| < epsilion, could be really given a
significant speed edge
if done in a single go in hardware.
One thing to ponder here is that "thinks" like this are what lead
to CISC instruction messes. It just seems obvious to people that
it will help efficiency to have highly specialized instructions,
but in practice they gum up the architecture with junk, and a
careful analysis shows that the actual gain is small at best.
How many applications spend a significant amount of time doing
such an epsilon test -- best guess: none.
Well actually you are interpreting too much wight in to my speculations.
I was just curious whatever similar analysis has been already
seriously done?
And after all, well the most commonly used instruction set architectures
for numerical calculations, are not exactly what one would call "lean
and mean"...
People simply use what's already there and what is cheap.
Or could you imagine something uglier then the stacked/MMX/XMM/SSE4
mess?
After all even the supposedly competent instructions set designers
admitted their previous
fallacy by the introduction of SSE2.
Marcin Dalecki
