Understanding Computer Architecture
Extra materials for the combined MIPSfpga and Connected MCU seminar by Imagination Technologies
October-November 2016

Quiz 3.2. Compiling C into MIPS Assembly
Name ___________________________________________________________________

1. What is the purpose of using program stack in assembly (and any other) programming?

a) Stack is needed to store return addresses for the nested function calls
b) Stack is used to pass function parameters when there is no place on registers
c) Stack is used to allocate space for temporary variables when there is no place on registers
d) Stack is used to save some temporary registers when calling a function
e) All the above

2. What MIPS assembly code corresponds to the following C code?

int f (int a, int b)
{
    int i, sum;

    for (i = a; i <= b; i++)
        sum += i;

    return sum;
}

////////// a //////////

f:
	li	$3,1
	beq	$4,$3,.L3
	li	$3,2

	beq	$4,$3,.L6
	nop

	bne	$4,$0,.L9
	nop

	lw	$2,%gp_rel(a)($28)
	j	$31
	sltu	$2,$0,$2

.L3:
	li	$2,2
	lw	$3,%gp_rel(b)($28)
	j	$31
	movz	$2,$0,$3

.L6:
	move	$2,$0
.L9:
	j	$31
	nop

////////// b //////////

f:
	addiu	$sp,$sp,-24
	sw	$31,20($sp)
	sw	$16,16($sp)
	move	$16,$4
	beq	$4,$0,.L2
	li	$2,1

	jal	f
	addiu	$4,$4,-1

	mul	$2,$2,$16
.L2:
	lw	$31,20($sp)
	lw	$16,16($sp)
	j	$31
	addiu	$sp,$sp,24

////////// c //////////

f:
	slt	$3,$5,$4
	bne	$3,$0,.L5
	nop

	addu	$2,$2,$4
.L4:
	addiu	$4,$4,1
	slt	$3,$5,$4
	beq	$3,$0,.L4
	addu	$2,$2,$4

	subu	$2,$2,$4
.L5:
	j	$31
	nop

////////// d //////////

f:
	nor	$2,$0,$6
	and	$5,$2,$5
	and	$4,$4,$6
	or	$2,$5,$4
	j	$31
	sw	$2,%gp_rel(e)($28)

////////// e //////////

f:
	lui	$3,%hi(a)
	addiu	$3,$3,%lo(a)
	addiu	$5,$3,40
.L3:
	lw	$4,0($3)
	addiu	$3,$3,4
	bne	$3,$5,.L3
	addu	$2,$2,$4

	j	$31
	nop

///////////////////////

Quiz is created by Yuri Panchul