Trivial Example request

[Neil Croft]

OK, mentioned elsewhere I like to learn by example. So, could some assembler guru demonstrate to the assembled (joke. Geddit?) newbs viewing, how the following (I'm particularly interested in the loops) would code out?

(and I appreciate this is trivial and could gain any number of performance improvements by things such as backward loops etc. If that's all you see then you've missed the point.)

FUNCTION PBMAIN () AS LONG
    c&=0    
    FOR a&=1 TO 10
        FOR b&=a&+1 TO 11
            c&=c+a&+b&
        NEXT
    NEXT
    PRINT c&
    WAITKEY$
END FUNCTION

[Paul Dixon]

Neil,
there are many ways to do it, here's one straight forward translation of your BASIC into ASM.

Paul.

#REGISTER NONE                 'advise you stop compiler using register variales while you experiment with ASM, it can cause confusion

FUNCTION PBMAIN () AS LONG
LOCAL a&,b&,c&                 'variables used in ASM must be referenced somewhere before you use them

    'c&=0
    !mov c&,0                  'mov 0 to c&
    
    'FOR a&=1 TO 10
    !mov a&,1                  'move 1 to a&
    aloop:
        'FOR b&=a&+1 TO 11
        !mov eax,a&            'get a& into register. Can only have 1 memory reference in an instruction so need to go via a register, eax
        !add eax,1             'add 1 to value of a& in eax
        !mov b&,eax            'move result to b
        bloop:

            'c&=c&+a&+b&
            !mov eax,c&        'eax = c&
            !add eax,a&        'eax = c& + a&
            !add eax,b&        'eax = c& + a& + b&
            !mov c&,eax        'move result in eax to c&

        'NEXT
        !add b&,1              'add 1 to b&
        !cmp b&,11             'has it exceeded the loop limit?
        !jle bloop             'it's less than or equal so no, loop back.

    'NEXT
    !add a&,1                  'add 1 to a&
    !cmp a&,10                 'compare with loop limit
    !jle aloop                 'it's less than or equal so loop back


    PRINT c&                   'stick to BASIC for printing.
    WAITKEY$
    
END FUNCTION

[Neil Croft]

Top stuff. I particularly like the way that PB can be used to avoid all the nasty I/O stuff (disks and output etc.) and all the register storing stuff too.

I found this http://www.arl.wustl.edu/~lockwood/c...ofasm/toc.html which gives a fairly broad view of assembler too so no doubt I shall be causing GPFs for the rest of the weekend whilst I mess around. :laugh:

[Neil Croft]

Paul,

Just a quick note to say I've played with your code and extended it to my needs on a couple of programs and I'm well impressed. Many thanks. Expect more questions soon and if you're ever in Micklebring then -> :beer:

[Paul Dixon]

Neil,

if you're ever in Micklebring

It's a bit far South for me, I don't often get beyond the North York Moors.

Paul.

[Neil Croft]

Neil,

It's a bit far South for me, I don't often get beyond the North York Moors.

Paul.

You haven't missed much. Far prettier up there.