31 lines
926 B
Plaintext
31 lines
926 B
Plaintext
// This file is part of www.nand2tetris.org
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// and the book "The Elements of Computing Systems"
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// by Nisan and Schocken, MIT Press.
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// File name: projects/08/FunctionCalls/FibonacciElement/Main.vm
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// Computes the n'th element of the Fibonacci series, recursively.
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// n is given in argument[0]. Called by the Sys.init function
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// (part of the Sys.vm file), which also pushes the argument[0]
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// parameter before this code starts running.
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function Main.fibonacci 0
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push argument 0
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push constant 2
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lt // checks if n<2
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if-goto IF_TRUE
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goto IF_FALSE
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label IF_TRUE // if n<2, return n
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push argument 0
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return
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label IF_FALSE // if n>=2, returns fib(n-2)+fib(n-1)
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push argument 0
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push constant 2
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sub
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call Main.fibonacci 1 // computes fib(n-2)
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push argument 0
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push constant 1
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sub
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call Main.fibonacci 1 // computes fib(n-1)
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add // returns fib(n-1) + fib(n-2)
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return
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