Ok so my assignment is to make a calculator, that given input from a textfile, will determine what I am to calculate. I am then to make a program that decodes the instruction, and runs the proper calculation according to the input. I am not having trouble loading the input or anything, I am having a problem where, every one of my functions runs regardless. So when I try to add something, it gets added, subtracted, and multiplied, etc.
Here is my current code:
.globl _start
@ error code values
@ you can easily load these like: mov r0,#ERR_OP_UNDEFINED
.equ ERR_NONE, 0x00000000
.equ ERR_OP_UNDEFINED, 0x00000001
.equ ERR_OP_OVERFLOW, 0x00000002
.equ ERR_OP_DIV_BY_ZERO, 0x00000003
_start:
@ set up r0 with _operandA
@ for example:
@ldr r3,=_operandA
@ldr r0,[r3] @ r0 := mem[r3]
ldr r3,=_operandA
ldr r0,[r3] @ r0 := mem[r3]=operandA r0 contains the first variable
ldr r3,=_operandB
ldr r1,[r3] @ r1 := mem[r3]=operandB r1 contains the second
ldr r3,=_operation
ldr r2,[r3] @ r2 :=mem[r3]=operation r2 contains the number corresponding to
the operation I am supposed to execute
all of these load properly
@ modify appropriately based on input arguments (e.g., decode _operation)
@These compare statements are what im not quite understanding correctly...
@Why the hell do they all execute, when only one of them should...
@note I am requred to use bl
cmpeq r2,#1
mov r8,#5 @test this compare
bl executeAdd
cmpeq r2, #2
mov r9,#6 @test this compare
bl executeSubtract
cmpeq r2, #3
mov r10,#7 @test this compare
bl executeMultiply
cmpeq r2, #4
mov r11,#8 @test this compare
bl executeDivide
cmpeq r2, #5
mov r12,#9 @test this compare
bl executeNegate
@the instructor added this here and it is required to be here
iloop: b iloop @ leave this infinite loop at the end of your program (needed for grading)
@ write execution procedures here:
@ I started by writing the first 3
@ Note I am required to use bx lr at the end of the procedure
executeAdd:
cmp r2,#1
mov r4,#0
add r4,r0,r1 @ r4 := r0+r1
mov r2,#99
bx lr
executeSubtract:
mov r5,#0
sub r5,r0,r1 @ r5 := r0-r1
mov r2,#99
bx lr
executeMultiply:
mov r6,#8
mul r6,r0,r1 @r6 := r0*r1
mov r2,#99
bx lr
executeDivide:
mov r2,#99
bx lr
executeNegate:
mov r2,#99
bx lr
stop:
end
@ write error handling procedures here:
@ NOTE: you'll want to use the stack here, since these handlers may be called from other functions (e.g., handleDivByZero will be called by executeDivide)
handleUndefined:
bx lr
handleOverflow:
bx lr
handleDivByZero:
bx lr
And here is my resulting output to the registers after I am finished:
http://gyazo.com/3d168de21ddb6a6b9171d70261810303
I placed 5,6,7,8 in registers 8,9,10,11,12 in order to test the compare statement, and they all execute..
