Question

Write a program named subtract.asm that does the following using LC3 assembly language:

Print a prompt "PRESS TWO KEYS: " Note that the prompt MUST LOOK EXACTLY like the above, with a colon and a space after the word KEYS with no newline. Get a two key press from the user. Subtract the second characters ASCII code from the first characters ASCII code. If the result is positive, print the word POSITIVE. Turn in subtract.asm to the appropriate submission point on Web-CAT.

• All of this code should be in your main portion of the program You do not need subroutines.  
• You are not allowed to use subroutines and therefore do not need to save registers.

Answer 1

HERE is the CODE:

.LC0:

        .string "PRESS TWO KEYS: "

.LC1:

        .string "%c%c"

.LC2:

        .string "POSITIVE"

.LC3:

        .string "NEGATIVE"

main:

        push    rbp

        mov     rbp, rsp

        sub     rsp, 16

        mov     edi, OFFSET FLAT:.LC0

        mov     eax, 0

        call    printf

        lea     rdx, [rbp-2]

        lea     rax, [rbp-1]

        mov     rsi, rax

        mov     edi, OFFSET FLAT:.LC1

        mov     eax, 0

        call    __isoc99_scanf

        movzx   eax, BYTE PTR [rbp-1]

        movsx   edx, al

        movzx   eax, BYTE PTR [rbp-2]

        movsx   eax, al

        sub     edx, eax

        mov     eax, edx

        test    eax, eax

        jle     .L2

        mov     edi, OFFSET FLAT:.LC2

        mov     eax, 0

        call    printf

        jmp     .L4

.L2:

        mov     edi, OFFSET FLAT:.LC3

        mov     eax, 0

        call    printf

.L4:

        nop

        leave

        ret

SCREENSHOT: