57 lines
1.8 KiB
NASM
57 lines
1.8 KiB
NASM
bits 32 ; assembling for the 32 bits architecture
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; declare the EntryPoint (a label defining the very first instruction of the program)
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global start
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; declare external functions needed by our program
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extern exit ; tell nasm that exit exists even if we won't be defining it
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import exit msvcrt.dll ; exit is a function that ends the calling process. It is defined in msvcrt.dll
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; msvcrt.dll contains exit, printf and all the other important C-runtime specific functions
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; our data is declared here (the variables needed by our program)
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segment data use32 class=data
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; ...
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a db 10
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b dw 2
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c dd 3
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d db 4
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f dw 1
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g dw 2
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x dq 2
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; our code starts here
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segment code use32 class=code
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start:
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; ...
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mov al,[a] ;AL=a
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cbw ;AX=a
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imul word [b] ;DX:AX=a*b
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push dx ;stack: dx,
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push ax ;stack: dx,ax
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mov al,[d] ;AL=d
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cbw ;AX=d
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cwde ;EAX=d
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mov ecx,[c] ;ECX=c
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sub ecx,eax ;ECX=c-d
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pop eax ;EAX=a*b , stack:
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cdq ;EDX:EAX=a*b
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idiv dword ecx ;EAX=(a*b)/(c-d)
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mov ecx,eax ;ECX=(a*b)/(c-d)
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mov ax,[f] ;AX=f
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imul word [g] ;DX:AX=f*g
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push dx ;stack: DX
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push ax ;stack: DX,AX
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pop eax ;EAX=f*g , stack:
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add eax,ecx ;EAX=(a*b)/(c-d)+f*g
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cdq ;EDX:EAX=(a*b)/(c-d)+f*g
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add [x],eax
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adc [x+4],edx
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; exit(0)
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push dword 0 ; push the parameter for exit onto the stack
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call [exit] ; call exit to terminate the program
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