Code Confusion....

Kenneth Kramer

Hi everybody,

Consider the following code:

·mov a,#10
·mov b,a··; b := a
:loop
·sub a,b··; if 0 set z := 1
·jz :loop·; if z == 0 then jump :loop
·nop··; if z == 1 then <nop>

however, this code executes as:

·mov a,#10
·mov b,a··; b := a
:loop
·sub a,b··; if 0 set z·:= 1
·jz :loop·; if z == 1 then jump :loop
·nop··; if z == 0 then <nop>

when using the SXSim simulator.

Now, if a macro like:

ifz·macro·1
·sb STATUS.2
·jmp \1
endm

substitutes the <jz> compound statement such that:

·mov a,#10
·mov b,a
:loop
·sub a,b··; if 0 set z = 1
·ifz :loop·; if z == 0 then jump :loop
·nop··; if z == 1 then <nop>

which lead me to the conclusion that <jz> has the <snz> instruction implemented as <snb STATUS.2>. If that's the case (and it seems so) then the <jz> statement wiil never jump to the address in mind.

If this·bug (which I believe it is) has been fixed in later version(s), please forgive me - I couldn't resist·thinking about·the problem .

Thanks,
Kenneth

Post Edited By Moderator (Jon Williams) : 11/8/2004 2:34:44 PM GMT

Bean

I don't follow your comments.
In the first example you have

jz :loop ; if z==0 then jump :loop

The comment does NOT describe the action "jz" means jump if the zero flag is SET not if the zero flag is zero

Maybe that is the confusion.

Bean.

Kenneth Kramer

It was a mistake. I've done some assembler programming in the 8086 processor family over the years and I have always thought of the zero flag as being Z (zero) = 0 or NZ (non-zero) = 1. My apology to Mr. Daubach for mistakenly thinking of my problem as a bug in the SXSim simulator. Thanks for the input, Bean. It helped me a lot.


cheers,
Kenneth