;;; Shreyas Vaidya
;;; 115415522
;;; shreyasv

;;; Implementation that computes the nth fibonacci number.

    .global isqrt                 ; exposes fib as a label for the linker
isqrt:                            ; the label: the next instruction starts isqrt()
    ;; Add your code here.
    cpi r24, 2          ; if(n < 2) branch to 2
    cpc r25, r1
    brlo 2f
    movw r18, r24
    lsr r24         ; shifts n two bytes to right
    lsr r24
    mov r22, r24        ; moves n>>2 passed as parameter to r22
    mov r23, r25
    push r23
    push r22        ; recursive call for isqrt
    call isqrt
    pop r22         ; pops value from recursive call to r20
    pop r23
    lsl r24
    mov r22, r24        ; moves n>>2 passed as parameter to r22
    mov r23, r25        ; shifts small one byte to left
    mov r20, r22        ; storage for large (for mult)
    mov r21, r23
    inc r20         ; increments small
    mul r20, r20        ; large * large
    mov r20, r0     ; mult gets stored in r0, moved to r16
    clr r1
    cp r18, r20     ; if(n < large * large)
    brlo 3f
    cp r18, r20
    brge 4f

2:              ; returns n
    clr r25
    jmp 1f

3:  movw r24, r22       ; returns small
    jmp 1f

4:  inc r22         ; returns large
    movw r24, r22       ; returns small
    jmp 1f

1:
    ret                     ; returns.  necessary.