I'm coming back to assembly for the sake of it after a few months and I'm having trouble getting two numbers to multiply and output the result. Here's my code:
.386
.model flat, stdcall
option casemap :none
include \masm32\include\windows.inc
include \masm32\include\kernel32.inc
include \masm32\include\masm32.inc
includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\masm32.lib
.data
sum sdword 0
.code
start:
mov ecx, 6
xor eax, eax
mov edx, 7
mul edx
push eax
pop sum
lea eax, sum
call StdOut
push 0
call ExitProcess
end start
It outputs something like P &aeffiini,.
QUESTION: Why does it output that random character string, and how can I fix it?
Thanks in advance.
Because StdOut prints NULL terminated strings NOT numbers. You need to convert the number to a string first. MASM32 has dwtoa. Also, your multiplying wrong. you multiply with eax
include masm32rt.inc
.data?
lpBuffer db 12 dup (?)
.code
start:
mov ecx, 6
mov eax, 7
mul eax
push offset lpBuffer
push eax
call dwtoa
push offset lpBuffer
call StdOut
inkey
push 0
call ExitProcess
end start
Your output is controlled by whatever you have in the StdOut function, which you haven't shown us. More than likely (given your description), it takes the character code in the accumulator and outputs the equivalent character.
If that's the case, what you probably need to do is to take the value in eax and work out which characters need to be output based on that. Then, call StdOut for each of them.
The pseudo-code for that would be something like:
eax <- value to print
call print_num
exit
print_num:
compare eax with 0
branch if not equal, to non_zero
eax <- hex 30 ; Number was zero,
jump to StdOut ; just print single digit 0
non_zero:
push eax, ebx, ecx ; Save registers that we use
ecx <- 0 ; Digit count
loop1:
compare eax with 0 ; Continue until digits all pushed
jump if equal, to num_pushed
increment ecx ; Another digit
ebx <- eax ; Work out what it is
eax <- eax / 10
eax <- eax * 10
ebx <- ebx - eax
push ebx to stack ; Then push it,
jump to loop1 ; and carry on
num_pushed:
pop eax from stack ; Get next digit
eax <- eax + hex 30 ; Print it out
call StdOut
decrement ecx ; One less digit to go
jump if not zero, to num_pushed ; Continue if more
pop ecx, ebx, eax from stack ; Clean up stack and return
return
If that's not the case, you will simply have to figure out what StdOut actually does and adjust your code to meet the requirements of that function.
