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@opt stack_pointer RG
@opt csr_scratch RF
@use ext_std:*
@label program
; call fibo subroutine with parameter 10
ldi RA 10
csi fibo
hlt
@label fibo
; function fibo
; parameters:
; RA n : u16
; return value:
; RA fibo(n) : u16
spu RB ; prelude
spu RC
subi RA 2 RA ; if n < 2, return n
bri f_sign fibo_early
spu RD ; prelude
ldi RB 0 ; a = 0
ldi RC 1 ; b = 1
@label fibo_loop
add RB RC RD ; v = a + b
mov RC RB ; a = b
mov RD RC ; b = v
dec RA ; n -= 1
bri f_zero fibo_done ; loop while n > 0
jpi fibo_loop
@label fibo_early
spo RC
spo RB
rsr
@label fibo_done
mov RD RA
spo RD ; restore registers
spo RC
spo RB
rsr
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