Question

Write the MIPS assembly version of this C code:

int weird(char[] s, int x)
{
  int i;
  for (i = 0; i < x; i++) { 
    if (s[i] == ‘A’)
    {
        return power(10, i);
    }
  }
  return -1;
}

int power(int base, int i)
{
    int j = 0;
    while (j < base)
    {
        base = base * base;
        j++;
    }
    return base;
}

Answer 1

MIPS GCC 5.4 Code for the given c code:

power(int, int):

addiu $sp,$sp,-24

sw $fp,20($sp)

move $fp,$sp

sw $4,24($fp)

sw $5,28($fp)

sw $0,8($fp)

$L3:

lw $3,8($fp)

lw $2,24($fp)

nop

slt $2,$3,$2

beq $2,$0,$L2

nop

lw $3,24($fp)

lw $2,24($fp)

nop

mult $3,$2

mflo $2

sw $2,24($fp)

lw $2,8($fp)

nop

addiu $2,$2,1

sw $2,8($fp)

b $L3

nop

$L2:

lw $2,24($fp)

move $sp,$fp

lw $fp,20($sp)

addiu $sp,$sp,24

j $31

nop

weird(char*, int):

addiu $sp,$sp,-40

sw $31,36($sp)

sw $fp,32($sp)

move $fp,$sp

sw $4,40($fp)

sw $5,44($fp)

sw $0,24($fp)

$L9:

lw $3,24($fp)

lw $2,44($fp)

nop

slt $2,$3,$2

beq $2,$0,$L6

nop

lw $2,24($fp)

lw $3,40($fp)

nop

addu $2,$3,$2

lb $3,0($2)

li $2,65 # 0x41

bne $3,$2,$L7

nop

lw $5,24($fp)

li $4,10 # 0xa

jal power(int, int)

nop

b $L8

nop

$L7:

lw $2,24($fp)

nop

addiu $2,$2,1

sw $2,24($fp)

b $L9

nop

$L6:

li $2,-1 # 0xffffffffffffffff

$L8:

move $sp,$fp

lw $31,36($sp)

lw $fp,32($sp)

addiu $sp,$sp,40

j $31

nop

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