From: "Ed Jaffe" <[email protected]> To: <[email protected]> Sent: Saturday, 16 March 2013 4:27 AM
In the original S/360, nearly all instructions that manipulated binary integers treated them as signed quantities.
AL, SL, ALR, SLR come to mind. These were intended to facilitate multiple-precision arithmetic.
(It's the reason that 32K is a limit in so many places in z/OS e.g., block sizes, number of ASIDs, etc.)
No it's not. It's the result of using the halfword instructions such as LH, AH, SH, etc which automatically sign-extend to 32 bits. (Incidentally, the high-order 16 bits can easily be set to zero.)
