project08 template files

08/FunctionCalls/FibonacciElement/Main.vm

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+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: projects/8/FunctionCalls/FibonacciElement/Main.vm
+
+// Contains one function: Main.fibonacci.
+
+// Computes the n'th element of the Fibonacci series, recursively.
+// n is given in argument[0]. Called by the Sys.init function 
+// (part of the Sys.vm file), which sets argument[0] to an input
+// value and then calls Main.fibonacci.
+function Main.fibonacci 0
+	push argument 0
+	push constant 2
+	lt                     
+	if-goto N_LT_2        
+	goto N_GE_2
+label N_LT_2               // if n < 2 returns n
+	push argument 0        
+	return
+label N_GE_2               // if n >= 2 returns fib(n - 2) + fib(n - 1)
+	push argument 0
+	push constant 2
+	sub
+	call Main.fibonacci 1  // computes fib(n - 2)
+	push argument 0
+	push constant 1
+	sub
+	call Main.fibonacci 1  // computes fib(n - 1)
+	add                    // returns fib(n - 1) + fib(n - 2)
+	return