what does -(A7) or (A7)+ mean

Shafqat's Avatar
Go4Expert Member

I'm a beginner at assembly language and I have a piece of code I'm trying to understand. I understand most of it but I still am not sure what -(A7) or (A7)+ mean.

I know An are address registers and so A7 is the last 32 bit address register (coldfire processor). But whats the -/+ before and after?

Is it decrementing or incrementing?

If so, what is being incremented or decremented? The address registers themselves?

e.g. does -(A7) mean A6?

xpi0t0s's Avatar, Join Date: Aug 2004
-(A7) dereferences and predecrements A7, in C++ this would be *(--A7)
(A7)+ dereferences and postincrements A7, in C++ *(A7++).

-(A7) decreases the value in A7 by 1, then looks up in memory what is at address A7. So if we have the following memory layout:

0012bcad 41
0012bcae 37
0012bcaf 26

and A7 contains 0012bcae, move.b -(A7),d0 will change A7 to 0012bcad and load 41 into d0.
Mirroring that, if A7 contains 0012bcae, move.b (A7)+,d0 will load 37 into d0 and change A7 to 0012bcaf.
Shafqat's Avatar
Go4Expert Member
That helped a lot, thank you