Re: The best place to begin learning Assembler

Thanks for the clarification

One says it sets the condition code "No Carry" (ALR) the other says "n/o"
(ar) which
I think means "no overflow"


On Wed, May 26, 2010 at 12:27 PM, PeterH <[email protected]> wrote:

>
>
>
> On May 26, 2010, at 12:14 PM, Ron Hudson wrote:
>
> > (I noticed AR and ALR seem to be the same instruction??)
>
> AR and ALR are different.
>
> The first is 2's complement whereas the second is 1's complement.
>
> It is important to have both instructions available, particularly if
> one is going to be using double-word (meaning, 64-bit) integer
> operations which are simulated using two ALRs in sequence, branching
> around the second should the high-order word NOT need to be adjusted
> by an AL =F'1'.
>
> This option is often important when taking an integer which is 64-
> bits in width, and needs to be converted into a floating-point number.
>
> Remember, the TOD clock is a 64-bit integer, and taking the beginning
> TOD (STCK) and the ending TOD (STCK) values, and then forming the
> difference, hence the elapsed-time, requires these 64-bit operations,
> but it also usually gives a 32-bit result.
>
>  
>