🚀 go-pugleaf

In article <1990Jul9.163607.18336@sunee.waterloo.edu> gpsteffl@sunee.waterloo.edu (Glenn Patrick Steffler) writes:

   Lets take a real world example:

   A spread sheet program which must perform several thousand iterations
   of a formula while recalculating.  The formula can be "compiled" to
   the stack, and run such that the execution time is considerably less
   than if the formula had been interpreted each time.

   A video device driver or some such that uses raster ops to write values
   to the video display.  (Given the Amiga has a blitter with this ability
   I do not ask for confirmation of the relevance of this arguement)  The
   driver can "compile" a raster operation fill algorithm into some small
   code segment and run it.  This is indeed self modifying code, but is 
   almost essential for speed, because the user hates to wait for screen
   refresh.

Both examples are from a class that's often confused with self
modifying code, but aren't really self modifying unless badly written.
I call that class (until somebody suggests something better) self
generating code.

All programs of this class can be done without modifying code -
remember, you're creating it, not modifying it! For the first example
(several thousand iterations? trivial) I'd compile to interpreted
stack-machine code to run. For large applications (popi, for instance)
or those where speed is more critical (your video driver), compile to
an array and tell the OS you're launching a task loaded into that
chunk of memory, and use that. The OS should take care of making sure
the code in that memory actually gets run, and not whatever you put
there last time around.

Of course, for your video applications, you wouldn't want to use a
soft solution anyway. Either a blitter, or a hand-coded library for
all the common operations, or a graphics accelerator that does all the
real work. In any of those cases, you never need to generate or modify
code; that's already been done. For development, you'd want the
support code that finally runs the code you're developing to be as
straightforward as possible, and raw speed won't be that critical.

	<mike
--
My feet are set for dancing,				Mike Meyer
Won't you turn your music on.				mwm@relay.pa.dec.com
My heart is like a loaded gun,				decwrl!mwm
Won't you let the water run.