MIPS Assembly Lang help

[Dojo2000]

I need some help with MAL. My professor seems to think we can magically figure out assembler errors even though this is our very first MAL program. I've got the program itself down. It calculates the sum of 1, 3, and 7 using only subtraction.
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">#
# *** Equivalences ***
#
print_int = 1

#
# *** Data ***
#
.data
x: .word 1
y: .word 3
z: .word 7

###
### *** Instructions ***
###

.text
main: sub $s0, $0, x # subtract x from 0
sub $s0, $s0, y # subtract y from that
sub $s0, $s0, z # subtract z from that
sub $s1, $0, $s0 # subtract answer from 0
li $v0, print_int
lw $a0, $s1
syscall

jr $ra</pre>[/QUOTE]I'm getting the following parse error when I try to load the file into the assembler
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">spim: (parser) parse error on line 28 of file onlysub.s
sub $s0, $0, x # subtract x from 0
^</pre>[/QUOTE]I have no idea what its complaining about.

[95Batmobile]

It's complaining about the spim paser sub file! STOOPID! [img]tongue.gif[/img]

Looks like Greek to me.

[98Camaro3.8]

I'm not familiar with MIPS, but should "main:" be on a seperate line from the code perhaps?

Also when you say "sub $s0, $0, x", I believe that's subtracting x from register 0, not the number 0. Doesn't look like you load anything into register 0 before that.

Edit: n/m the $0. I guess $0 is a constant, while $1 and up are registers.

[Infernal]

Well, it's been about 10 years since I've touched assembly languages, but I'll take a guess and say that you cannot use a defined constant as an operand to an opcode. You've got:

sub $s0, $0, x

I would suggest trying:

lw $t1, x
sub $t0, $0, $t1

... and change the other sub opcode calls as well.

[Dojo2000]

Thanks guys. I finally caught up with my professor and he pointed out that I can't use variables in my operand specifiers, but you can use constants, like "X = 1"

$0 is register 0, and is always a zero

I also needed to "move" the answer into $a0, not load

For those that care it looks like this now
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;"> .text
main: lw $s5, x # load x into $s5
lw $s6, y # load y into $s6
lw $s7, z # load z into $s7
sub $s0, $0, $s5 # subtract x from 0
sub $s0, $s0, $s6 # subtract y from that
sub $s0, $s0, $s7 # subtract z from that
sub $s1, $0, $s0 # subtract answer from 0
li $v0, print_int
move $a0, $s1
syscall

jr $ra # return to OS</pre>[/QUOTE]

[ March 03, 2005, 05:01 PM: Message edited by: Dojo2000 ]

[Infernal]

It makes sense. The variables would be treated as addresses in the data segment of the application, and the opcodes can only act on registers or constant values. The reason defined constants like your x, y and z work is because they are swapped out for the actual values in the code before it is compiled.