MIPS: Addressing and Decisions( Endereçamento e decisões)

Decisions in MIPS (decisões)


Instruction for decisions in MIPS( instruções de decisão) :

*  beq registo1, registo2, L1
*  beq means "branch if equal"

Same as (C): 
  if ( registo1== registo2) goto L1

Instruction supplementary decision in MIPS(Instrução de decisão complementar):

* bne registo1, registo2, L1
* bne means “branch if not equal”

Same as (C): 
  if ( registo1 != registo2) goto L1

"Goto" statement in MIPS(instrução "goto"):

It is the jump instruction ("jump") jumps directly to "label" indicated 

without checking any condition.

For example:

In C:

if (i == j) f=g+h; 

else f=g-h; 

 pseudo instruction                MIPS

if(condicion) goto TRUE;    beq $S3,$S4,TRUE
Code FALSE;                     sub $S0,$S1,$S2
goto NEXT;                         j NEXT
TRUE code TRUE;          TRUE
                                           add $S0,$S1,$S2
NEXT:                               NEXT


Another example:

In C:

do { 
g = g + A[i]; 
i = i + j;

} while (i != h); 

where g,h,i,j,base of A, $s1, $s2, $s3, $s4, $s5

pseudo instruction:

LOOP:  g=g+A[i]
             i=i+j;
             if(i!=h) goto LOOP;


MIPS:

LOOP : sll $St1,$S3,2 # St1=4*I
             //Construction of the vector
             add $t1,$t1,$S5  #St1=addr A[i] (address position for A[i])
              lw $t1,0($t1) # $t1=A[i]
             add $S1,$S1,$t1 # g= g+A[i]
             add $S3,$S3,$S4 # i=i+j
             bne $S3,$S2,LOOP # goto LOOP
                                               # if(i!=h)