83 lines
2.5 KiB
Plaintext
83 lines
2.5 KiB
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/11/ConvertToBin/Main.jack
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/**
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* Unpacks a 16-bit number into its binary representation:
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* Takes the 16-bit number stored in RAM[8000] and stores its individual
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* bits in RAM[8001..8016] (each location will contain 0 or 1).
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* Before the conversion, RAM[8001]..RAM[8016] are initialized to -1.
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*
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* The program should be tested as follows:
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* 1) Load the program into the supplied VM emulator
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* 2) Put some value in RAM[8000]
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* 3) Switch to "no animation"
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* 4) Run the program (give it enough time to run)
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* 5) Stop the program
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* 6) Check that RAM[8001]..RAM[8016] contains the correct binary result, and
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* that none of these memory locations contains -1.
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*/
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class Main {
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/**
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* Initializes RAM[8001]..RAM[8016] to -1,
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* and converts the value in RAM[8000] to binary.
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*/
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function void main() {
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var int value;
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do Main.fillMemory(8001, 16, -1); // sets RAM[8001]..RAM[8016] to -1
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let value = Memory.peek(8000); // reads a value from RAM[8000]
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do Main.convert(value); // performs the conversion
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return;
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}
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/** Converts the given decimal value to binary, and puts
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* the resulting bits in RAM[8001]..RAM[8016]. */
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function void convert(int value) {
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var int mask, position;
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var boolean loop;
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let loop = true;
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while (loop) {
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let position = position + 1;
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let mask = Main.nextMask(mask);
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if (~(position > 16)) {
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if (~((value & mask) = 0)) {
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do Memory.poke(8000 + position, 1);
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}
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else {
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do Memory.poke(8000 + position, 0);
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}
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}
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else {
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let loop = false;
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}
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}
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return;
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}
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/** Returns the next mask (the mask that should follow the given mask). */
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function int nextMask(int mask) {
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if (mask = 0) {
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return 1;
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}
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else {
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return mask * 2;
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}
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}
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/** Fills 'length' consecutive memory locations with 'value',
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* starting at 'startAddress'. */
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function void fillMemory(int startAddress, int length, int value) {
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while (length > 0) {
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do Memory.poke(startAddress, value);
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let length = length - 1;
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let startAddress = startAddress + 1;
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}
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return;
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}
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}
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