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Old 12 May 2007, 04:36   #1
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Join Date: Mar 2007
Location: Gothenburg / Sweden
Age: 45
Posts: 977
Learning assembler

Just started to learn myself assembler, I'm pretty good at c++, java and some other languages, however I want to learn Amiga assembler now. Tried it about 15 years ago, but I found it too hard then...

Ok, so I did a little program, it should find the biggest number in the list and save it in D1. Every time a run the progam D1 contains F00 though, I did some debuggin and it looks like A0 gets incremented by 2 every time, instead of 1. So where did I f-ed up? (And please don't laugh)
        clr.l   d0          ;clear registers
        clr.l   d1
        move.w  amount,d0   ;assign size of list to d0
        lea.l   list,a0     ;point to beginning of list
loop    cmp(a0)+,d1         ;is current number bigger than the one in d1?
        bls save            ;if so, go to save
cont    sub.w   #1,d0       ;decrement list counter
        bne.s   loop        ;go back and check next number
        rts                 ;no more numbers in list
save    move.w  -1(a0),d1   ;save current number-1 to d1
        bra cont            ;go back

amount  dc.w    5
list    dc.w    15,2,23,4,3
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Old 12 May 2007, 05:00   #2
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Location: Auckland / New Zealand
Posts: 3,165
The main problem is you have move.w -1(a0),d1 in the save part. This is an illegal operation on a 68000 as you are moving a word but it is not word aligned, so it will crash. On a 68020+ that code will work.

To fix it, you need it to be move.w -2(a0),d1

If you are serious about learning, you should start with good habits as you will keep them as you learn:

cmp.w (a0)+,d1 instead of cmp (a0)+,d1
moveq #0,d0 instead of clr.l d0
lea list(pc),a0 instead of lea.l list,a0

Instead of hardwiring the amount as 5, calculate the length etc:

        lea     list(pc),a0
        move.w  #(listend-list)>>1,d0
list    dc.w    15,2,23,4,3
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