eceg431/08/ProgramFlow/FibonacciSeries/FibonacciSeries.vm

// 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/ProgramFlow/FibonacciSeries/FibonacciSeries.vm

// Puts the first n elements of the Fibonacci series in the memory,
// starting at address addr. n and addr are given in argument[0] and
// argument[1], which must be initialized by the caller of this code.

	push argument 1         // sets THAT, the base address of the
	pop pointer 1           // that segment, to argument[1]
	push constant 0         // sets the series' first and second
	pop that 0              // elements to 0 and 1, respectively       
	push constant 1   
	pop that 1              
	push argument 0         // sets n, the number of remaining elements
	push constant 2         // to be computed, to argument[0] minus 2,
	sub                     // since 2 elements were already computed.
	pop argument 0          

label LOOP
	push argument 0
	if-goto COMPUTE_ELEMENT // if n > 0, goto COMPUTE_ELEMENT
	goto END                // otherwise, goto END

label COMPUTE_ELEMENT
    // that[2] = that[0] + that[1]
	push that 0
	push that 1
	add
	pop that 2
	// THAT += 1 (updates the base address of that)
	push pointer 1
	push constant 1
	add
	pop pointer 1 
	// updates n-- and loops          
	push argument 0
	push constant 1
	sub
	pop argument 0          
	goto LOOP

label END