Assembly

help with assembly assignment

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Join Date: Oct 2009

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amw2326

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help with assembly assignment

Oct 21st, 2009

so I am working on an assignment in class, and I've hit a road block. the assignment is to replace certain letters (b, c) with others, (x, y). Right now, my program is not recognizing 'b' in ebx, and the second letter in the array, 'b', (stored in eax) as being the same, so it is not changing them. I know im doing something wrong, but I can't figure out what. Any hints would be much appreciated, meanwhile i will keep plugging away at it. Also, I cannot get the new array in edx to show up without subtracting sixteen, and im not sure how to fix that so that is not necessary. Thanks so much.

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INCLUDE Irvine32.inc
.data
     array byte 'a', 'b', 'c', 'd', 'e', 'f', 'a', 'b', 'c',
                'd', 'e', 'f', 'a', 'b', 'c'
     letter byte ?
     newArray byte 15 dup (?)
.code
main PROC
     mov ecx, lengthof array           ;moves ecx to beginning of array as a counter
     mov esi, offset array           ;moves esi to the beginning of array to obtain letters
     mov eax, [esi]                   ;moves first position of array into eax
 
     doLoop:                        ;starts a loop
     mov ebx, 'b'                   ;moves first letter comparison (b) into ebx
     cmp ebx, eax                    ;compares letters
     je check4C                        ;if it is b, then jump to check for c
     add edx, eax					;if not b, store first letter of newArray in edx
     add esi, type array            ; increment esi to next letter in array
 
     loop doLoop                    ;loop back to the beginning
 
     mov edx, offset newArray
     sub edx, 16
 
     call writestring                ;print newArray string with new letters
     call crlf                        ;enters a blank line
     call waitmsg                    ;waits til user closes screen
 
     exit                            ;exit
 
     check4C:                        ;check for c
     add edx, 'x'                ;adds x for b into new array
     add esi, type array            ;move esi down the array
     mov eax, [esi]                    ;move esi into eax for next comparison
     mov ebx, 'c'                    ;move c into ebx for comparison
     cmp ebx, eax                    ;compare registers
     je replace                        ;if the letter is matches c go to replace
     add edx, eax                 ;store next letter of newArray in edx
     add esi, type array            ;move esi down the array
     jmp doLoop                        ;go to the top of the loop
 
     replace:                        ;replaces y for c
     add edx, 'y'                ;moves y into array instead of c
     add esi, type array            ;move esi down the array
     jmp doLoop                        ;go to the top of the loop
 
main ENDP  
 
END main
INCLUDE Irvine32.inc
.data
     array byte 'a', 'b', 'c', 'd', 'e', 'f', 'a', 'b', 'c',
                'd', 'e', 'f', 'a', 'b', 'c'
     letter byte ?
     newArray byte 15 dup (?)
.code
main PROC
     mov ecx, lengthof array           ;moves ecx to beginning of array as a counter
     mov esi, offset array           ;moves esi to the beginning of array to obtain letters
     mov eax, [esi]                   ;moves first position of array into eax
    
     doLoop:                        ;starts a loop
     mov ebx, 'b'                   ;moves first letter comparison (b) into ebx
     cmp ebx, eax                    ;compares letters
     je check4C                        ;if it is b, then jump to check for c
     add edx, eax					;if not b, store first letter of newArray in edx
     add esi, type array            ; increment esi to next letter in array

     loop doLoop                    ;loop back to the beginning
   
     mov edx, offset newArray
     sub edx, 16

     call writestring                ;print newArray string with new letters
     call crlf                        ;enters a blank line
     call waitmsg                    ;waits til user closes screen
   
     exit                            ;exit
   
     check4C:                        ;check for c
     add edx, 'x'                ;adds x for b into new array
     add esi, type array            ;move esi down the array
     mov eax, [esi]                    ;move esi into eax for next comparison
     mov ebx, 'c'                    ;move c into ebx for comparison
     cmp ebx, eax                    ;compare registers
     je replace                        ;if the letter is matches c go to replace
     add edx, eax                 ;store next letter of newArray in edx
     add esi, type array            ;move esi down the array
     jmp doLoop                        ;go to the top of the loop
   
     replace:                        ;replaces y for c
     add edx, 'y'                ;moves y into array instead of c
     add esi, type array            ;move esi down the array
     jmp doLoop                        ;go to the top of the loop

main ENDP  

END main

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Join Date: Oct 2008

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NotNull

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Oct 21st, 2009

mov eax, dword [esi] ;moves first position of array into eax
And also moves a double word EAX=44434241h, I think so,
not sure.

To read each byte at a time do:
xor eax, eax
mov al, byte [esi]

mov ebx, 'b' ;moves first letter comparison (b) into ebx
cmp ebx, eax ;compares letters EAX=44434241h EBX=00000042h
je check4C

Last edited by NotNull; Oct 21st, 2009 at 10:10 pm.

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