>This brings to mind the relative speed increase of register variables.
>Does anyone know how much faster it would be to have a variable in
>a register than on the stack?
>M

>> >You can't put function parameters in registers because they are
>> >passed on the stack.

In 68K, all parameters are indeed passed on the stack. But in PPC,
registers are used to pass up to 8 parameters of the right kind (integer,
long, pointer, and so on). If you have register on, they stay in registers.
If register is off, they get transferred from the registers to become, in
effect, local variables on the stack. Sometimes it's desirable to force
this explicitly, for example if you want your true local vars to be
register but the parameters use up all available registers:

register off
local fn Test(a, b, c, d, e, f, g, h) // parameters becomes RAM vars
register on
dim j as long, k as long.... // up to 8 register vars
....

The reason for using this technique is that parameters are most often
"read-only" variables. There's not much speed advantage in having them in
registers, because they are loaded extremely quickly from the PPC cache.
You get a more significant speedup by putting "variable value" variables
into registers, and these are (usually) your FN's local vars. Derek
explained that such "variable" variables get both read and written: hence
the advantage of registers.

BrianHughes@... wrote:
>Maybe this is too simplistic to work or maybe I'm doing something
>wrong but the code below showed almost no difference.
  <  code example snipped  >

All the variables in your code example are globals, and hence cannot be
register. See below for a working demo, or put END GLOBALS at the top of
your code. (In the demo below, END GLOBALS doesn't affect the timing,
because that's based entirely on FN vars and parameters).

Robert P.


end globals

register off
local fn LoopsNoRegister(n as long)
dim j as long, x as long
for j = 1 to n: inc(x): dec(x): inc(x): dec(x): next
end fn

register on
local fn LoopsRegister(n as long)
dim j as long, x as long
for j = 1 to n: inc(x): dec(x): inc(x): dec(x): next
end fn

_nLoop = 5000000
print "loops " _nLoop
dim ticks as long
ticks = fn tickcount: fn LoopsNoRegister(_nLoop)
ticks = fn tickcount - ticks
print "No register "ticks " ticks"
ticks = fn tickcount: fn LoopsRegister(_nLoop)
ticks = fn tickcount - ticks
print "Register "ticks " ticks"