fibonacci.asm

.globl main
.globl fibonacci

.data
some_error_occurred: .asciiz "*** Some error occurred.\n"

.text
main:
    sub $sp, $sp, 4
    sw $ra, 0($sp)
    sub $sp, $sp, 4
    sw $fp, 0($sp)
    move $fp, $sp

    sub $sp, $sp, 4
    li $t0, 20
    sw $t0, 0($sp)
    jal fibonacci
    add $sp, $sp, 4

    move $a0, $v0
    li $v0, 1
    syscall
    li $a0, 0x0a
    li $v0, 11
    syscall

    move $sp, $fp
    lw $fp, 0($sp)
    add $sp, $sp, 4
    lw $ra, 0($sp)
    add $sp, $sp, 4
    jr $ra

fibonacci:
    sub $sp, $sp, 4
    sw $ra, 0($sp)
    sub $sp, $sp, 4
    sw $fp, 0($sp)
    move $fp, $sp

    sub $sp, $sp, 8
    sw $s0, -4($fp)
    sw $s1, -8($fp)

    lw $t0, 8($fp)
    blez $t0, fail
    li $t1, 2
    ble $t0, $t1, fibonacci_base_case
    sub $sp, $sp, 4
    sub $t0, $t0, 1
    sw $t0, 0($sp)
    jal fibonacci
    move $s0, $v0
    sub $sp, $sp, 4
    lw $t0, 8($fp)
    sub $t0, $t0, 2
    sw $t0, 0($sp)
    jal fibonacci
    move $s1, $v0
    add $v0, $s0, $s1
    j return_fibonacci

fibonacci_base_case:
    move $v0, $t0
    sub $v0, $v0, 1

return_fibonacci:
    lw $s1, -8($fp)
    lw $s0, -4($fp)
    add $sp, $sp, 8

    move $sp, $fp
    lw $fp, 0($sp)
    add $sp, $sp, 4
    lw $ra, 0($sp)
    add $sp, $sp, 4
    jr $ra

fail:
    la $a0, some_error_occurred
    li $v0, 4
    syscall
    li $a0, -1
    li $v0, 17
    syscall