Re: Stealing a Great Idea from the 6600

George Neuner wrote:

On Sun, 21 Apr 2024 00:43:21 +0000, mitchalsup@aol.com (MitchAlsup1)
wrote:

Address arithmetic is ADD only and does not care about signs or
overflow. There is no concept of a negative base register or a
negative index register (or, for that matter, a negative displace-
ment), overflow, underflow, carry, ...

Stack frame pointers often point to the middle of the frame and need
to access data using both positive and negative displacements.

Yes, one accesses callee saved registers with positive displacements
and local variables with negative accesses. One simply needs to know
where the former stops and the later begins. ENTER and EXIT know this
by the register count and by the stack allocation size.

Some GC schemes use negative displacements to access object headers.

Those are negative displacements not negative bases or indexes.