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@opt stack_pointer RG
@opt csr_scratch RH
@use ext_std:*
; bootstrap code (must be called to setup mandatory data)
; will jump to label main
@include bootstrap
@label main
; call fibo subroutine with parameter 10
ldi 10 RA
csi fibo
hlt
@label fibo
;;; subroutine fibo
;;; param RA N
;;; return RA Nth fibonacci number
; store RB, RC on stack
spu RB
spu RC
; if n < 2, return n
subi RA 2 RA
bri sign fibo_early
; store also RD on stack
spu RD
; a = 0
ldi 0 RB
; b = 1
ldi 1 RC
@label fibo_loop
; v = a + b
add RB RC RD
; a = b
mov RC RB
; b = v
mov RD RC
; n -= 1
dec RA
; loop while n > 0
bri zero fibo_done
jpi fibo_loop
@label fibo_early
; restore used registers
spo RC
spo RB
; return from subroutine
rsr
@label fibo_done
mov RD RA
; restore used registers
spo RD
spo RC
spo RB
; return from subroutine
rsr
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