MIPS useful snippets

Loops

Loop 1 (increment)

for(int i = 12; i<34; i++){
    // do A
}
// do B

    addi	$t0, $0, 12
    addi	$t1, $0, 34
L1: 
    beq		$t0, $t1, exit

    // do A

    addi	$t0, $t0, 1
    j		L1
exit:
    // do B

Loop 2 (decrement)

for(int i = 34; i>12; i--){
    // do A
}
// do B

    addi	$t0, $0, 34
    addi	$t1, $0, 12
L1: 
    beq		$t0, $t1, exit

    // do A

    addi	$t0, $t0, -1
    j		L1
exit:
    // do B

Loop 3 (while loop blocking)

while(a == b){
    // do A
}
// do B

L1: 
    bne		$t0, $t1, exit
    // do A
exit:
    // do B

Loop 4: execute body `counter` times

# while loop body executed 100 times (counter)
i = 0;
j = 0;
counter = 100;
do{
    i += 4;
    j += 8;
    counter--;
}while(counter != 0)
// finally

# t0 (counter), t1 (i), t2(j)
addi	$t0, $0, 100
addi	$t1, $0, 0
addi	$t2, $0, 0

L1: 
    // do something, starting with i = 0, j = 0

    addi	$t1, $t1, 4
    addi	$t2, $t2, 8
    addi	$t0, $t0, -1

bne		$t0, $0, L1

// finally

Loop 5: 2D array

# a0: array address, a1: #rows, a2: #columns

# loop j*i times

# t0 = j*i, t1 = starts from a0 (then will go up in 4's
mult	$a1, $a2
mflo	$t0
addi	$t1, $a0, 0

L1:
    # load element
    lw		$t2, 0($t1)

    # t2 now contains the element under consideration
    
    

    addi	$t1, $t1, 4
    addi	$t0, $t0, -1

bne		$t0, $0, L1

 

Conditionals

Conditional 1

if(a == b){
    // do A
}
// do B

# say $t0 = a, $t1 = b
bne		$t0, $t1, B	
A:
    // do A
B: 
    // do B

Conditional 2

if(a != b){
    // do A
}
// do B

# say $t0 = a, $t1 = b
beq		$t0, $t1, B	
A:
    // do A
B: 
    // do B

Memory access

Access 1: Access variable X,  given its address:

# Given X address ($t0), access X and put it into $t2 or $f12

# Case 1: X is integer 
lw		$t2, 0($t0)

# Case 2: X is single precision float
lwc1    $f12, 0($t0)

# Case 3: X is double precision float (little endian)
lwc1    $f12, 0($t0)
lwc1    $f13, 4($t0)

# Case 3-a: X is double precision float (big endian)
lwc1    $f12, 4($t0)
lwc1    $f13, 0($t0)

Access 2: Access W[i], given address of W

# Given W ($t0), i ($t1), access W[i] and store it to $t2 or $f12 (if float)
# Here, we are effectively using $t2 as a temporary var

# Case 1: W is integer 
addi	$t2, $t2, 4
mult	$t1, $t2
mflo	$t2	
add		$t2, $t0, $t2       # t2 = 4*i + W
lw		$t2, 0($t2)		    # t2 = W[i] 

# Case 2: W is single precision float
addi	$t2, $t2, 8
mult	$t1, $t2			
mflo	$t2				
add		$t2, $t0, $t2       # t2 = 4*8 + W
lwc1    $f12, 0($t2)

# Case 3: W is double precision float (little endian)
addi	$t2, $t2, 8
mult	$t1, $t2			
mflo	$t2				
add		$t2, $t0, $t2       # t2 = 4*8 + W
lwc1    $f12, 0($t2)
lwc1    $f13, 4($t2)

Function

Function 1: Declare v0 function(a0, a1)

# Function 1: Declare `v0 function(a0, a1)`
# where a0, a1 are parameters, and v0 is return value (set to 5)

Func1: 
    add		$t0, $0, $a0
    add		$t1, $0, $a1

    # Do stuff
    addi	$v0, $0, 5
    
    jr		$ra

Calling Function 1, not caring about overriden $ra 

main:
    add		$a0, $t0, $0
    add		$a1, $t1, $0
    jal		Func1
    # now v0 is populated with 5

 

Function 2: using stack pointer to pass >4 variables to a function as argument.

Refer to Lecture 4-6A, slide 38

 

 

 

Appendices

Appendix 1: Main CPU registers alias

Appendix 2: Crossing register values between processors

Appendix 3: defining literal values

Appendix 4: Conversion (fd = destination register, fs = source register)

Appendix 5: Register Conventions

 

Appendix 6: compare operations

Compare floating point then jump

note: bc1t is used like `bc1t <label>`

Compare integers