Make LispM code FREE (fwd)

William A. Barnett-Lewis
Wed, 01 Apr 1998 15:45:56 -0600

P. T. Withington wrote:
> On 4/1/98 15:22, William A. Barnett-Lewis wrote:
> >P. T. Withington wrote:
> >>
> >> On 3/31/98 23:41, Chris Hanson wrote:
> >>
> >> >At 10:05 PM -0600 3/31/98, Chris Bitmead wrote:

> Well there were several Lisp emulators written:  one to emulate the chip
> at the gate level and one that emulated the chip at the instruction
> level, both used to debug ported software before the chip was ready.  The
> C and assembly were both inspired by the instruction emulator.  The big
> hit on performance was emulating a 40-bit word on a 32-bit machine.
> Alpha makes that easier, being a 64-bit machine.  And only the core
> execution engine was in assembly, there was lots of supporting C code 
>-- the VM implementation for instance, was written mostly in C.  The
> tightest assembley was required for memory read/write which on the Lisp
> hardware does tag checking, invisible pointer following, and gc barriers.
>  In the end, a LispM read took 7 Alpha cycles.

Ah. The word size differences; that makes somewhat more sense. Would
this allevied by the P2 and PPC being 64 bit internally? They would
still be choked by the bus width, but it shouldn't be as big a hit as
emulating 40 bits in 32. 

Perhaps it would be best, overall, to make the jump to a full 64 bit
implementation...     !


Live without fear; your Creator loves you
as a mother. Go in peace to follow the good
road and may God's blessing be with you always.
St. Claire