[Mono-devel-list] Prevalence of pointer-integral-pointer casting in mono?
jeroen at sumatra.nl
Mon Aug 9 03:12:31 EDT 2004
Peter Colson wrote:
> The underlying architecture is PPC. Not sure of all the
> details but it doesn't use 128-bit registers. The 128-pit
> pointers are an OS/compiler construct to provide
> a single address space (memory and disk together).
It's been a while since I read about the AS/400 achitecture, but I think
that the AS/400 uses a *modified* PowerPC chip that has special support
for the AS/400 memory model.
The AS/400 memory model is very interesting because it doesn't allow
native machine code to do pointer arithmetic. Only privileged code can
create pointers. In the pre-PowerPC days, every memory word had an
additional (hidden) bit that signaled if the word contained a valid
pointer or not. This bit couldn't be manipulated from user code (wasn't
even visible). I don't know how they do it nowadays.
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