Piet van Oostrum wrote:
Arne Vajhøj <[EMAIL PROTECTED]> (AV) wrote:
AV> Robert Maas, http://tinyurl.com/uh3t wrote:
John W Kennedy <[EMAIL PROTECTED]> wrote:
JWK> Into the 60s, indeed, there were still machines being made
JWK> that had no instruction comparable to the mainframe BASx/BALx
JWK> family, or to Intel's CALL. You had to do a subprogram call by
JWK> first overwriting the last instruction of what you were
JWK> calling with a branch instruction that would return back to
JWK> you.
That's not true, that you needed to do that, that there was no
other way available. The subroutine linkage I invented for S.P.S.
(Symbolic Programming System, i.e. IBM 1620 assembly language) was
to reserve a 5-digit space immediately before the subroutine entry
point for storing the return address. So the caller needed to know
only one address, the entry point, and do both store-return-address
and jump relative to that address, rather than needing to know both
the entry point and the last-instruction-JUMP-needs-patch address
as independent items of information.
AV> CDC Cyber did something very similar.
AV> Not very recursion friendly.
Actually, the CYBER way wasn't too bad. IIRC the CYBER had a subroutine
instruction that stored the return address in the location that the
instruction referenced and then jumped to the address following that
location. To implement a recursive procedure you started the code of the
procedure with saving the return address to a stack.
It was of course doable.
Else Pascal would have been hard to implement.
Arne
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