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diff --git a/resources/asm/fibo.atk16 b/resources/asm/fibo.atk16
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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