possible OR branch mips32?

Question

i'm trying to find a way to do something like bOR $a0, $a1, $a2 else, something like if(a=b||a=c){blablabla}else{blabla} in java, but i don't figure out a way to do it in mips32. Any idea?

Answer 1

Assume you have a in $a0, b in $a1 and c in $a2 then you would do

  beq $a0, $a1, if
  beq $a0, $a2, if
  bgez $zero, else
if:
    .. code if a=b or a=c
  bgez $zero, endif
else:
    .. code otherwise
endif:

Answer 2

It's been ages since I did any assembly, but since no one has responded, here's what I remember. I hope you accept this answer, if for no other reason than that I'm re-living my worst nightmares for you.

To do any kind of logic in assembly, you'll need to do comparisons, followed by conditional jumps. So for instance, an if/else statement of the form:

if (a == b || a == c) {
    cond1
}
else {
    cond2
}
cond3

Would be translated as follows (pseudo-code):

    cmp a,b
    je cond1
    cmp a,c
    je cond1
    ...
cond2:
    ...
    jmp cond3

cond1:
    ...
cond3:
    ...

Cmp compares values, and je is a conditional branch that jumps if the last comparison showed the values are equal. Basically, you're using gotos all over the place. Again, that's the pseudo-code, but you should easily find the MIPS analogs.

Speaking of which, I found this: http://jjc.hydrus.net/cs61c/handouts/loops4.pdf

Answer 3

x86 code, but it should give an idea.

    cmp     eax, ebx
    je      blablabla
    cmp     eax, ecx
    jne     blabla

blablabla: ; if a == b || a == c
    ;do your blablabla sutff here
    jmp     Continue

blabla: ; else
    ;do your blabla sutff here

Continue: