Re: PDP-11 compat mode [was Re: New Vax - future directions :-)]

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> I usually think of the carry as an extra bit left to the most
> significant bit of the register involved; [...]

> The VAX just has the actual C bit inverted after the operation (set
> to 1 if there was need to borrow, instead of 0 because it was
> borrowed from).  So you *could* describe it as "(a) borrow into most
> significant bit (happened)".

That's a logically consistent point of view.  But it requires that the
"most significant bit" text refer to this one-bit-wider conceptual
value formed by concatenating the complement of C with the overt
operand.

That's not how "most significant bit" works elsewhere in the document,
nor how it works in most other uses I've seen/heard of such language.

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