MIPS: Recursion

Question

I'm trying to do this code in MIPS language for some days and don't had any good results, I don't know what to do!! Can you help me? thank you"

int function1(int n){
    if (n <= 2)
       return -15;
    else{
        int comp = 6*function1(n-1) + (-2)*function1(n-2) + 3*n;
        return comp;
    }
}

Answer 1

The approach is quite simple. It is modified Fibonacci function, where coefficients are added with each recursive call. Code follows:

    .text

#recursive recurent function. similar as fibonacci, with smaller modifications
RecurentFunction:
    sub     $sp,    $sp,    12                      #allocate 12B on stack
    sw      $ra,    0($sp)                          #save return address
    sw      $a0,    4($sp)                          #save argument

    ble     $a0,    2,      exit_recurentfunction   #if argumrnt is <= 2 go to exit and return -15
    sub     $a0,    $a0,    1                       #set n = n - 1
    jal     RecurentFunction                        #recursive call
    mulo    $v0,    $v0,    6                       #multiply result with 6, as requested: 6*function1(n-1)
    sw      $v0,    8($sp)                          #save result

    lw      $a0,    4($sp)                          #load argument, as it's overwrittent by previous calls
    sub     $a0,    $a0,    2                       #set n = n - 2
    jal     RecurentFunction                        #recursive call
    mulo    $v0,    $v0,    -2                      #multiply result with -2, as requested: (-2)*function1(n-2)

    lw      $t0,    8($sp)                          #load previous result
    add     $v0,    $v0,    $t0                     #add previous result to current result

    lw      $t0,    4($sp)                          #load argument, as it's overwrittent by previous calls
    mulo    $t0,    $t0,    3                       #multiply by 3, as requested: 3*n
    add     $v0,    $v0,    $t0                     #add to result

    lw      $ra,    0($sp)                          #load return address
    addi    $sp,    $sp,    12                      #free stack
    jr      $ra                                     #return

exit_recurentfunction:
    li      $v0,    15
    lw      $ra,    0($sp)                          #load return address
    addi    $sp,    $sp,    12                      #free stack
    jr      $ra                                     #return

main:
    li      $a0,    4                               #set $a0 = 54, argument for function call
    jal     RecurentFunction                        #call RecurentFunction

    move    $a0,    $v0                             #move result to $a0
    li      $v0,    1                               #set $v0 = 1, system call for print int
    syscall

    li      $v0,    10                              #set $v0 = 10, system call for exit program
    syscall

.data

Hope it helps