1 files changed, 66 insertions, 0 deletions
diff --git a/asm/fibo.atk16 b/asm/fibo.atk16
new file mode 100644
index 0000000..8bb7a6e
--- /dev/null
+++ b/asm/fibo.atk16
@@ -0,0 +1,66 @@
+@opt stack_pointer RF
+@opt csr_scratch RH
+@use ext_std:*
+
+; jump over data segment
+  jpi program
+
+; data segment
+@label ram_offset
+  0x8000
+
+@label program
+; set up stack pointer to point to beginning of RAM
+  ldi ram_offset RA
+  ldr RA RF
+
+; call fibo subroutine with parameter 10
+  ldi 10 RA
+  csi fibo
+  hlt
+
+@label fibo
+; function fibo
+; parameters:
+;  RA   n : u16
+; return value:
+;  RA   fibo(n) : u16
+
+; 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