So I have been learning assembly and working on a small project for class. Its a simple program that multiples two numbers without using the built in mult instruction. Instead it does so by shift adding. But I am having trouble making it display the result in the QtSpim console.
.text
main:
li $v0, 0
li $t0, 1
li $t1, 0
li $a0, 2
li $a1, 3
main_loop:
beq $a1, $zero, main_end
beq $a0, $zero, main_end
and $t1, $t0, $a1
beq $t1, 1, main_do_add
beq $t1, 0, main_do_shift
main_do_add:
addu $v0, $v0, $a0
main_do_shift:
sll $a0, $a0, 1
srl $a1, $a1, 1
j main_loop
main_end:
li $v0, 10
I am very new to assembly and this is first real piece of program. So I am not sure what I am doing wrong.
You simply forgot to print the value.
Here's the corrected and annotated program. Note: I did not check your multiply logic, but the result was 6, so I'm guessing that's what you wanted.
I recommend adding sidebar comments to almost every asm line so you can follow your logic and compare it against the instructions you use to implement it.
Anyway, here's the code [please pardon the gratuitous style cleanup]:
.text
main:
li $v0,0
li $t0,1
li $t1,0
li $a0,2
li $a1,3
main_loop:
beq $a1,$zero,main_end
beq $a0,$zero,main_end
and $t1,$t0,$a1
beq $t1,1,main_do_add
beq $t1,0,main_do_shift
main_do_add:
addu $v0,$v0,$a0
main_do_shift:
sll $a0,$a0,1
srl $a1,$a1,1
j main_loop
main_end:
# BUGFIX -- this was missing
move $a0,$v0 # get result to argument register
li $v0,1 # print integer
syscall
li $v0,10 # exit program
syscall