From a000308104aab27c2dde9a306f1bc654b2db4806 Mon Sep 17 00:00:00 2001
From: Yuchen Pei <me@ypei.me>
Date: Wed, 29 Nov 2017 12:30:41 +0100
Subject: first commit

---
 projects/12/Array.jack                          |  23 +++
 projects/12/ArrayTest/ArrayTest.cmp             |   2 +
 projects/12/ArrayTest/ArrayTest.tst             |  15 ++
 projects/12/ArrayTest/Main.jack                 |  40 +++++
 projects/12/Keyboard.jack                       |  62 ++++++++
 projects/12/KeyboardTest/KeyboardTestOutput.gif | Bin 0 -> 12048 bytes
 projects/12/KeyboardTest/Main.jack              |  93 +++++++++++
 projects/12/Math.jack                           |  47 ++++++
 projects/12/MathTest/Main.jack                  |  35 ++++
 projects/12/MathTest/MathTest.cmp               |   2 +
 projects/12/MathTest/MathTest.tst               |  15 ++
 projects/12/Memory.jack                         |  34 ++++
 projects/12/MemoryTest/Main.jack                |  42 +++++
 projects/12/MemoryTest/MemoryTest.cmp           |   2 +
 projects/12/MemoryTest/MemoryTest.tst           |  15 ++
 projects/12/Output.jack                         | 203 ++++++++++++++++++++++++
 projects/12/OutputTest/Main.jack                |  42 +++++
 projects/12/OutputTest/OutputTestOutput.gif     | Bin 0 -> 6184 bytes
 projects/12/Screen.jack                         |  43 +++++
 projects/12/ScreenTest/Main.jack                |  36 +++++
 projects/12/ScreenTest/ScreenTestOutput.gif     | Bin 0 -> 4563 bytes
 projects/12/String.jack                         |  64 ++++++++
 projects/12/StringTest/Main.jack                |  83 ++++++++++
 projects/12/StringTest/StringTestOutput.gif     | Bin 0 -> 8126 bytes
 projects/12/Sys.jack                            |  27 ++++
 projects/12/SysTest/Main.jack                   |  31 ++++
 26 files changed, 956 insertions(+)
 create mode 100644 projects/12/Array.jack
 create mode 100644 projects/12/ArrayTest/ArrayTest.cmp
 create mode 100644 projects/12/ArrayTest/ArrayTest.tst
 create mode 100644 projects/12/ArrayTest/Main.jack
 create mode 100644 projects/12/Keyboard.jack
 create mode 100644 projects/12/KeyboardTest/KeyboardTestOutput.gif
 create mode 100644 projects/12/KeyboardTest/Main.jack
 create mode 100644 projects/12/Math.jack
 create mode 100644 projects/12/MathTest/Main.jack
 create mode 100644 projects/12/MathTest/MathTest.cmp
 create mode 100644 projects/12/MathTest/MathTest.tst
 create mode 100644 projects/12/Memory.jack
 create mode 100644 projects/12/MemoryTest/Main.jack
 create mode 100644 projects/12/MemoryTest/MemoryTest.cmp
 create mode 100644 projects/12/MemoryTest/MemoryTest.tst
 create mode 100644 projects/12/Output.jack
 create mode 100644 projects/12/OutputTest/Main.jack
 create mode 100644 projects/12/OutputTest/OutputTestOutput.gif
 create mode 100644 projects/12/Screen.jack
 create mode 100644 projects/12/ScreenTest/Main.jack
 create mode 100644 projects/12/ScreenTest/ScreenTestOutput.gif
 create mode 100644 projects/12/String.jack
 create mode 100644 projects/12/StringTest/Main.jack
 create mode 100644 projects/12/StringTest/StringTestOutput.gif
 create mode 100644 projects/12/Sys.jack
 create mode 100644 projects/12/SysTest/Main.jack

(limited to 'projects/12')

diff --git a/projects/12/Array.jack b/projects/12/Array.jack
new file mode 100644
index 0000000..ee31129
--- /dev/null
+++ b/projects/12/Array.jack
@@ -0,0 +1,23 @@
+// 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/12/Array.jack
+
+/**
+ * Represents an array.
+ * In the Jack language, arrays are instances of the Array class.
+ * Once declared, the array entries can be accessed using the usual
+ * syntax arr[i]. Each array entry can hold a primitive data type as 
+ * well as any object type. Different array entries can have different 
+ * data types.
+ */
+class Array {
+
+    /** Constructs a new Array of the given size. */
+    function Array new(int size) {
+    }
+
+    /** Disposes this array. */
+    method void dispose() {
+    }
+}
diff --git a/projects/12/ArrayTest/ArrayTest.cmp b/projects/12/ArrayTest/ArrayTest.cmp
new file mode 100644
index 0000000..d1a9798
--- /dev/null
+++ b/projects/12/ArrayTest/ArrayTest.cmp
@@ -0,0 +1,2 @@
+|RAM[8000]|RAM[8001]|RAM[8002]|RAM[8003]|
+|     222 |     122 |     100 |      10 |
diff --git a/projects/12/ArrayTest/ArrayTest.tst b/projects/12/ArrayTest/ArrayTest.tst
new file mode 100644
index 0000000..89934b9
--- /dev/null
+++ b/projects/12/ArrayTest/ArrayTest.tst
@@ -0,0 +1,15 @@
+// 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/12/ArrayTest/ArrayTest.tst
+
+load,
+output-file ArrayTest.out,
+compare-to ArrayTest.cmp,
+output-list RAM[8000]%D2.6.1 RAM[8001]%D2.6.1 RAM[8002]%D2.6.1 RAM[8003]%D2.6.1;
+
+repeat 1000000 {
+  vmstep;
+}
+
+output;
diff --git a/projects/12/ArrayTest/Main.jack b/projects/12/ArrayTest/Main.jack
new file mode 100644
index 0000000..439770a
--- /dev/null
+++ b/projects/12/ArrayTest/Main.jack
@@ -0,0 +1,40 @@
+// 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/12/ArrayTest/Main.jack
+
+/** Test program for the OS Array class. */
+class Main {
+
+    /** Performs several Array manipulations. */
+    function void main() {
+        var Array r;                  // stores test results
+        var Array a, b, c;
+        
+        let r = 8000;
+        
+        let a = Array.new(3);
+        let a[2] = 222;
+        let r[0] = a[2];              // RAM[8000] = 222
+        
+        let b = Array.new(3);
+        let b[1] = a[2] - 100;
+        let r[1] = b[1];              // RAM[8001] = 122
+        
+        let c = Array.new(500);
+        let c[499] = a[2] - b[1];
+        let r[2] = c[499];            // RAM[8002] = 100
+        
+        do a.dispose();
+        do b.dispose();
+        
+        let b = Array.new(3);
+        let b[0] = c[499] - 90;
+        let r[3] = b[0];              // RAM[8003] = 10
+        
+        do c.dispose();
+        do b.dispose();
+        
+        return;
+    }
+}
diff --git a/projects/12/Keyboard.jack b/projects/12/Keyboard.jack
new file mode 100644
index 0000000..03e1031
--- /dev/null
+++ b/projects/12/Keyboard.jack
@@ -0,0 +1,62 @@
+// 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/12/Keyboard.jack
+
+/**
+ * A library for handling user input from the keyboard.
+ */
+class Keyboard {
+
+    /** Initializes the keyboard. */
+    function void init() {
+    } 
+
+    /**
+     * Returns the character of the currently pressed key on the keyboard;
+     * if no key is currently pressed, returns 0.
+     *
+     * Recognizes all ASCII characters, as well as the following keys:
+     * new line = 128 = String.newline()
+     * backspace = 129 = String.backspace()
+     * left arrow = 130
+     * up arrow = 131
+     * right arrow = 132
+     * down arrow = 133
+     * home = 134
+     * End = 135
+     * page up = 136
+     * page down = 137
+     * insert = 138
+     * delete = 139
+     * ESC = 140
+     * F1 - F12 = 141 - 152
+     */
+    function char keyPressed() {
+    }
+
+    /**								
+     * Waits until a key is pressed on the keyboard and released,
+     * then echoes the key to the screen, and returns the character 
+     * of the pressed key.
+     */
+    function char readChar() {
+    }
+
+    /**								
+     * Displays the message on the screen, reads from the keyboard the entered
+     * text until a newline character is detected, echoes the text to the screen,
+     * and returns its value. Also handles user backspaces.
+     */
+    function String readLine(String message) {
+    }   
+
+    /**								
+     * Displays the message on the screen, reads from the keyboard the entered
+     * text until a newline character is detected, echoes the text to the screen,
+     * and returns its integer value (until the first non-digit character in the
+     * entered text is detected). Also handles user backspaces. 
+     */
+    function int readInt(String message) {
+    }
+}
diff --git a/projects/12/KeyboardTest/KeyboardTestOutput.gif b/projects/12/KeyboardTest/KeyboardTestOutput.gif
new file mode 100644
index 0000000..944983a
Binary files /dev/null and b/projects/12/KeyboardTest/KeyboardTestOutput.gif differ
diff --git a/projects/12/KeyboardTest/Main.jack b/projects/12/KeyboardTest/Main.jack
new file mode 100644
index 0000000..e89182c
--- /dev/null
+++ b/projects/12/KeyboardTest/Main.jack
@@ -0,0 +1,93 @@
+// 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/12/KeyboardTest/Main.jack
+
+/** Test program for the OS Keyboard class. */
+class Main {
+
+    /** Gets input from the user and verifies its contents. */
+    function void main() {
+    	var char c, key;
+    	var String s;
+    	var int i;
+    	var boolean ok;
+    
+        let ok = false;
+        do Output.printString("keyPressed test:");
+        do Output.println();
+        while (~ok) {
+            do Output.printString("Please press the 'Page Down' key");
+            while (key = 0) {
+                let key = Keyboard.keyPressed();
+            }
+            let c = key;
+            while (~(key = 0)) {
+                let key = Keyboard.keyPressed();
+            }
+        
+            do Output.println();
+        
+            if (c = 137) {
+       	        do Output.printString("ok");
+	            do Output.println();
+	            let ok = true;
+	        }
+	    }
+	
+	    let ok = false;
+        do Output.printString("readChar test:");
+        do Output.println();
+        do Output.printString("(Verify that the pressed character is echoed to the screen)");
+        do Output.println();
+        while (~ok) {
+            do Output.printString("Please press the number '3': ");
+    	    let c = Keyboard.readChar();
+        
+            do Output.println();
+        
+            if (c = 51) {
+	            do Output.printString("ok");
+	            do Output.println();
+	            let ok = true;
+	        }
+	    }
+	
+    	let ok = false;
+        do Output.printString("readLine test:");
+        do Output.println();
+        do Output.printString("(Verify echo and usage of 'backspace')");
+        do Output.println();
+        while (~ok) {
+    	    let s = Keyboard.readLine("Please type 'JACK' and press enter: ");
+
+	        if (s.length() = 4) {
+	            if ((s.charAt(0) = 74) & (s.charAt(1) = 65) & (s.charAt(2) = 67) & (s.charAt(3) = 75)) {
+	                do Output.printString("ok");
+   	                do Output.println();
+   	                let ok = true;
+   	            }
+    	    }
+    	}
+
+	    let ok = false;
+        do Output.printString("readInt test:");
+        do Output.println();
+        do Output.printString("(Verify echo and usage of 'backspace')");
+        do Output.println();
+        while (~ok) {
+  	        let i = Keyboard.readInt("Please type '-32123' and press enter: ");
+
+	        if (i = (-32123)) {
+	            do Output.printString("ok");
+	            do Output.println();
+	            let ok = true;
+	        }
+	    }
+        
+        do Output.println();
+        do Output.printString("Test completed successfully");
+        
+        return;
+    }
+}
diff --git a/projects/12/Math.jack b/projects/12/Math.jack
new file mode 100644
index 0000000..a57f023
--- /dev/null
+++ b/projects/12/Math.jack
@@ -0,0 +1,47 @@
+// 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/12/Math.jack
+
+/**
+ * A library of commonly used mathematical functions.
+ * Note: Jack compilers implement multiplication and division using OS method calls.
+ */
+class Math {
+
+    /** Initializes the library. */
+    function void init() {
+    }
+
+    /** Returns the absolute value of x. */
+    function int abs(int x) {
+    }
+
+    /** Returns the product of x and y. 
+     *  When a Jack compiler detects the multiplication operator '*' in the 
+     *  program's code, it handles it by invoking this method. In other words,
+     *  the Jack expressions x*y and multiply(x,y) return the same value.
+     */
+    function int multiply(int x, int y) {
+    }
+
+    /** Returns the integer part of x/y.
+     *  When a Jack compiler detects the multiplication operator '/' in the 
+     *  program's code, it handles it by invoking this method. In other words,
+     *  the Jack expressions x/y and divide(x,y) return the same value.
+     */
+    function int divide(int x, int y) {
+    }
+
+    /** Returns the integer part of the square root of x. */
+    function int sqrt(int x) {
+    }
+
+    /** Returns the greater number. */
+    function int max(int a, int b) {
+    }
+
+    /** Returns the smaller number. */
+    function int min(int a, int b) {
+    }
+}
diff --git a/projects/12/MathTest/Main.jack b/projects/12/MathTest/Main.jack
new file mode 100644
index 0000000..de5cec2
--- /dev/null
+++ b/projects/12/MathTest/Main.jack
@@ -0,0 +1,35 @@
+// 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/12/MathTest/Main.jack
+
+/** Test program for the OS Math class. */
+class Main {
+
+    /** Performs various mathematical operations, using calls to the Math class methods. */
+    function void main() {
+        var Array r;          // stores the test results;
+        
+        let r = 8000;
+    
+        let r[0] = 2 * 3;                  // 6
+        let r[1] = r[0] * (-30);           // 6 * (-30) = -180
+        let r[2] = r[1] * 100;             // (-180) * 100 = -18000
+        let r[3] = 1 * r[2];               // 1 * (-18000) = -18000
+        let r[4] = r[3] * 0;               // 0
+        
+        let r[5] = 9 / 3;                  // 3
+        let r[6] = (-18000) / 6;           // -3000
+        let r[7] = 32766 / (-32767);       // 0
+        
+        let r[8] = Math.sqrt(9);           // 3
+        let r[9] = Math.sqrt(32767);       // 181
+        
+        let r[10] = Math.min(345, 123);    // 123
+        let r[11] = Math.max(123, -345);   // 123
+        let r[12] = Math.abs(27);          // 27
+        let r[13] = Math.abs(-32767);      // 32767
+        
+        return;
+    }
+}
diff --git a/projects/12/MathTest/MathTest.cmp b/projects/12/MathTest/MathTest.cmp
new file mode 100644
index 0000000..703c1be
--- /dev/null
+++ b/projects/12/MathTest/MathTest.cmp
@@ -0,0 +1,2 @@
+|RAM[8000]|RAM[8001]|RAM[8002]|RAM[8003]|RAM[8004]|RAM[8005]|RAM[8006]|RAM[8007]|RAM[8008]|RAM[8009]|RAM[8010]|RAM[8011]|RAM[8012]|RAM[8013]|
+|       6 |    -180 |  -18000 |  -18000 |       0 |       3 |   -3000 |       0 |       3 |     181 |     123 |     123 |      27 |   32767 |
diff --git a/projects/12/MathTest/MathTest.tst b/projects/12/MathTest/MathTest.tst
new file mode 100644
index 0000000..127dbb4
--- /dev/null
+++ b/projects/12/MathTest/MathTest.tst
@@ -0,0 +1,15 @@
+// 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/12/MathTest/MathTest.tst
+
+load,
+output-file MathTest.out,
+compare-to MathTest.cmp,
+output-list RAM[8000]%D2.6.1 RAM[8001]%D2.6.1 RAM[8002]%D2.6.1 RAM[8003]%D2.6.1 RAM[8004]%D2.6.1 RAM[8005]%D2.6.1 RAM[8006]%D2.6.1 RAM[8007]%D2.6.1 RAM[8008]%D2.6.1 RAM[8009]%D2.6.1 RAM[8010]%D2.6.1 RAM[8011]%D2.6.1 RAM[8012]%D2.6.1 RAM[8013]%D2.6.1;
+
+repeat 1000000 {
+  vmstep;
+}
+
+output;
diff --git a/projects/12/Memory.jack b/projects/12/Memory.jack
new file mode 100644
index 0000000..941eec1
--- /dev/null
+++ b/projects/12/Memory.jack
@@ -0,0 +1,34 @@
+// 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/12/Memory.jack
+
+/**
+ * This library provides two services: direct access to the computer's main
+ * memory (RAM), and allocation and recycling of memory blocks. The Hack RAM
+ * consists of 32,768 words, each holding a 16-bit binary number.
+ */ 
+class Memory {
+
+    /** Initializes the class. */
+    function void init() {
+    }
+
+    /** Returns the RAM value at the given address. */
+    function int peek(int address) {
+    }
+
+    /** Sets the RAM value at the given address to the given value. */
+    function void poke(int address, int value) {
+    }
+
+    /** Finds an available RAM block of the given size and returns
+     *  a reference to its base address. */
+    function int alloc(int size) {
+    }
+
+    /** De-allocates the given object (cast as an array) by making
+     *  it available for future allocations. */
+    function void deAlloc(Array o) {
+    }    
+}
diff --git a/projects/12/MemoryTest/Main.jack b/projects/12/MemoryTest/Main.jack
new file mode 100644
index 0000000..77a53a9
--- /dev/null
+++ b/projects/12/MemoryTest/Main.jack
@@ -0,0 +1,42 @@
+// 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/12/MemoryTest/Main.jack
+
+/** Test program for the OS Memory class. */
+class Main {
+
+    /** Performs various memory manipulations. */
+    function void main() {
+        var int temp;
+        var Array a, b, c;
+        
+        do Memory.poke(8000, 333);       // RAM[8000] = 333
+        let temp = Memory.peek(8000);
+        do Memory.poke(8001, temp + 1);  // RAM[8001] = 334
+        
+        let a = Array.new(3);            // uses Memory.alloc
+        let a[2] = 222;
+        do Memory.poke(8002, a[2]);      // RAM[8002] = 222
+        
+        let b = Array.new(3);
+        let b[1] = a[2] - 100;
+        do Memory.poke(8003, b[1]);       // RAM[8003] = 122
+        
+        let c = Array.new(500);
+        let c[499] = a[2] - b[1];
+        do Memory.poke(8004, c[499]);     // RAM[8004] = 100
+        
+        do a.dispose();                   // uses Memory.deAlloc
+        do b.dispose();
+        
+        let b = Array.new(3);
+        let b[0] = c[499] - 90;
+        do Memory.poke(8005, b[0]);       // RAM[8005] = 10
+        
+        do c.dispose();
+        do b.dispose();
+        
+        return;
+    }
+}
diff --git a/projects/12/MemoryTest/MemoryTest.cmp b/projects/12/MemoryTest/MemoryTest.cmp
new file mode 100644
index 0000000..057958b
--- /dev/null
+++ b/projects/12/MemoryTest/MemoryTest.cmp
@@ -0,0 +1,2 @@
+|RAM[8000]|RAM[8001]|RAM[8002]|RAM[8003]|RAM[8004]|RAM[8005]|
+|     333 |     334 |     222 |     122 |     100 |      10 |
diff --git a/projects/12/MemoryTest/MemoryTest.tst b/projects/12/MemoryTest/MemoryTest.tst
new file mode 100644
index 0000000..1da34fd
--- /dev/null
+++ b/projects/12/MemoryTest/MemoryTest.tst
@@ -0,0 +1,15 @@
+// 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/12/MemoryTest/MemoryTest.tst
+
+load,
+output-file MemoryTest.out,
+compare-to MemoryTest.cmp,
+output-list RAM[8000]%D2.6.1 RAM[8001]%D2.6.1 RAM[8002]%D2.6.1 RAM[8003]%D2.6.1 RAM[8004]%D2.6.1 RAM[8005]%D2.6.1;
+
+repeat 1000000 {
+  vmstep;
+}
+
+output;
diff --git a/projects/12/Output.jack b/projects/12/Output.jack
new file mode 100644
index 0000000..18e3382
--- /dev/null
+++ b/projects/12/Output.jack
@@ -0,0 +1,203 @@
+// 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/12/Output.jack
+
+/**
+ * A library of functions for writing text on the screen.
+ * The Hack physical screen consists of 512 rows of 256 pixels each.
+ * The library uses a fixed font, in which each character is displayed 
+ * within a frame which is 11 pixels high (including 1 pixel for inter-line 
+ * spacing) and 8 pixels wide (including 2 pixels for inter-character spacing).
+ * The resulting grid accommodates 23 rows (indexed 0..22, top to bottom)
+ * of 64 characters each (indexed 0..63, left to right). The top left 
+ * character position on the screen is indexed (0,0). A cursor, implemented
+ * as a small filled square, indicates where the next character will be displayed.
+ */
+class Output {
+
+    // Character map for displaying characters
+    static Array charMaps; 
+
+    /** Initializes the screen, and locates the cursor at the screen's top-left. */
+    function void init() {
+    }
+
+    // Initializes the character map array
+    function void initMap() {
+        var int i;
+    
+        let charMaps = Array.new(127);
+        
+        // Black square, used for displaying non-printable characters.
+        do Output.create(0,63,63,63,63,63,63,63,63,63,0,0);
+
+        // Assigns the bitmap for each character in the charachter set.
+        // The first parameter is the character index, the next 11 numbers
+        // are the values of each row in the frame that represents this character.
+        do Output.create(32,0,0,0,0,0,0,0,0,0,0,0);          //
+        do Output.create(33,12,30,30,30,12,12,0,12,12,0,0);  // !
+        do Output.create(34,54,54,20,0,0,0,0,0,0,0,0);       // "
+        do Output.create(35,0,18,18,63,18,18,63,18,18,0,0);  // #
+        do Output.create(36,12,30,51,3,30,48,51,30,12,12,0); // $
+        do Output.create(37,0,0,35,51,24,12,6,51,49,0,0);    // %
+        do Output.create(38,12,30,30,12,54,27,27,27,54,0,0); // &
+        do Output.create(39,12,12,6,0,0,0,0,0,0,0,0);        // '
+        do Output.create(40,24,12,6,6,6,6,6,12,24,0,0);      // (
+        do Output.create(41,6,12,24,24,24,24,24,12,6,0,0);   // )
+        do Output.create(42,0,0,0,51,30,63,30,51,0,0,0);     // *
+        do Output.create(43,0,0,0,12,12,63,12,12,0,0,0);     // +
+        do Output.create(44,0,0,0,0,0,0,0,12,12,6,0);        // ,
+        do Output.create(45,0,0,0,0,0,63,0,0,0,0,0);         // -
+        do Output.create(46,0,0,0,0,0,0,0,12,12,0,0);        // .    
+        do Output.create(47,0,0,32,48,24,12,6,3,1,0,0);      // /
+        
+        do Output.create(48,12,30,51,51,51,51,51,30,12,0,0); // 0
+        do Output.create(49,12,14,15,12,12,12,12,12,63,0,0); // 1
+        do Output.create(50,30,51,48,24,12,6,3,51,63,0,0);   // 2
+        do Output.create(51,30,51,48,48,28,48,48,51,30,0,0); // 3
+        do Output.create(52,16,24,28,26,25,63,24,24,60,0,0); // 4
+        do Output.create(53,63,3,3,31,48,48,48,51,30,0,0);   // 5
+        do Output.create(54,28,6,3,3,31,51,51,51,30,0,0);    // 6
+        do Output.create(55,63,49,48,48,24,12,12,12,12,0,0); // 7
+        do Output.create(56,30,51,51,51,30,51,51,51,30,0,0); // 8
+        do Output.create(57,30,51,51,51,62,48,48,24,14,0,0); // 9
+        
+        do Output.create(58,0,0,12,12,0,0,12,12,0,0,0);      // :
+        do Output.create(59,0,0,12,12,0,0,12,12,6,0,0);      // ;
+        do Output.create(60,0,0,24,12,6,3,6,12,24,0,0);      // <
+        do Output.create(61,0,0,0,63,0,0,63,0,0,0,0);        // =
+        do Output.create(62,0,0,3,6,12,24,12,6,3,0,0);       // >
+        do Output.create(64,30,51,51,59,59,59,27,3,30,0,0);  // @
+        do Output.create(63,30,51,51,24,12,12,0,12,12,0,0);  // ?
+
+        do Output.create(65,0,0,0,0,0,0,0,0,0,0,0);          // A ** TO BE FILLED **
+        do Output.create(66,31,51,51,51,31,51,51,51,31,0,0); // B
+        do Output.create(67,28,54,35,3,3,3,35,54,28,0,0);    // C
+        do Output.create(68,15,27,51,51,51,51,51,27,15,0,0); // D
+        do Output.create(69,63,51,35,11,15,11,35,51,63,0,0); // E
+        do Output.create(70,63,51,35,11,15,11,3,3,3,0,0);    // F
+        do Output.create(71,28,54,35,3,59,51,51,54,44,0,0);  // G
+        do Output.create(72,51,51,51,51,63,51,51,51,51,0,0); // H
+        do Output.create(73,30,12,12,12,12,12,12,12,30,0,0); // I
+        do Output.create(74,60,24,24,24,24,24,27,27,14,0,0); // J
+        do Output.create(75,51,51,51,27,15,27,51,51,51,0,0); // K
+        do Output.create(76,3,3,3,3,3,3,35,51,63,0,0);       // L
+        do Output.create(77,33,51,63,63,51,51,51,51,51,0,0); // M
+        do Output.create(78,51,51,55,55,63,59,59,51,51,0,0); // N
+        do Output.create(79,30,51,51,51,51,51,51,51,30,0,0); // O
+        do Output.create(80,31,51,51,51,31,3,3,3,3,0,0);     // P
+        do Output.create(81,30,51,51,51,51,51,63,59,30,48,0);// Q
+        do Output.create(82,31,51,51,51,31,27,51,51,51,0,0); // R
+        do Output.create(83,30,51,51,6,28,48,51,51,30,0,0);  // S
+        do Output.create(84,63,63,45,12,12,12,12,12,30,0,0); // T
+        do Output.create(85,51,51,51,51,51,51,51,51,30,0,0); // U
+        do Output.create(86,51,51,51,51,51,30,30,12,12,0,0); // V
+        do Output.create(87,51,51,51,51,51,63,63,63,18,0,0); // W
+        do Output.create(88,51,51,30,30,12,30,30,51,51,0,0); // X
+        do Output.create(89,51,51,51,51,30,12,12,12,30,0,0); // Y
+        do Output.create(90,63,51,49,24,12,6,35,51,63,0,0);  // Z
+
+        do Output.create(91,30,6,6,6,6,6,6,6,30,0,0);          // [
+        do Output.create(92,0,0,1,3,6,12,24,48,32,0,0);        // \
+        do Output.create(93,30,24,24,24,24,24,24,24,30,0,0);   // ]
+        do Output.create(94,8,28,54,0,0,0,0,0,0,0,0);          // ^
+        do Output.create(95,0,0,0,0,0,0,0,0,0,63,0);           // _
+        do Output.create(96,6,12,24,0,0,0,0,0,0,0,0);          // `
+
+        do Output.create(97,0,0,0,14,24,30,27,27,54,0,0);      // a
+        do Output.create(98,3,3,3,15,27,51,51,51,30,0,0);      // b
+        do Output.create(99,0,0,0,30,51,3,3,51,30,0,0);        // c
+        do Output.create(100,48,48,48,60,54,51,51,51,30,0,0);  // d
+        do Output.create(101,0,0,0,30,51,63,3,51,30,0,0);      // e
+        do Output.create(102,28,54,38,6,15,6,6,6,15,0,0);      // f
+        do Output.create(103,0,0,30,51,51,51,62,48,51,30,0);   // g
+        do Output.create(104,3,3,3,27,55,51,51,51,51,0,0);     // h
+        do Output.create(105,12,12,0,14,12,12,12,12,30,0,0);   // i
+        do Output.create(106,48,48,0,56,48,48,48,48,51,30,0);  // j
+        do Output.create(107,3,3,3,51,27,15,15,27,51,0,0);     // k
+        do Output.create(108,14,12,12,12,12,12,12,12,30,0,0);  // l
+        do Output.create(109,0,0,0,29,63,43,43,43,43,0,0);     // m
+        do Output.create(110,0,0,0,29,51,51,51,51,51,0,0);     // n
+        do Output.create(111,0,0,0,30,51,51,51,51,30,0,0);     // o
+        do Output.create(112,0,0,0,30,51,51,51,31,3,3,0);      // p
+        do Output.create(113,0,0,0,30,51,51,51,62,48,48,0);    // q
+        do Output.create(114,0,0,0,29,55,51,3,3,7,0,0);        // r
+        do Output.create(115,0,0,0,30,51,6,24,51,30,0,0);      // s
+        do Output.create(116,4,6,6,15,6,6,6,54,28,0,0);        // t
+        do Output.create(117,0,0,0,27,27,27,27,27,54,0,0);     // u
+        do Output.create(118,0,0,0,51,51,51,51,30,12,0,0);     // v
+        do Output.create(119,0,0,0,51,51,51,63,63,18,0,0);     // w
+        do Output.create(120,0,0,0,51,30,12,12,30,51,0,0);     // x
+        do Output.create(121,0,0,0,51,51,51,62,48,24,15,0);    // y
+        do Output.create(122,0,0,0,63,27,12,6,51,63,0,0);      // z
+        
+        do Output.create(123,56,12,12,12,7,12,12,12,56,0,0);   // {
+        do Output.create(124,12,12,12,12,12,12,12,12,12,0,0);  // |
+        do Output.create(125,7,12,12,12,56,12,12,12,7,0,0);    // }
+        do Output.create(126,38,45,25,0,0,0,0,0,0,0,0);        // ~
+
+	return;
+    }
+
+    // Creates the character map array of the given character index, using the given values.
+    function void create(int index, int a, int b, int c, int d, int e,
+                         int f, int g, int h, int i, int j, int k) {
+	var Array map;
+
+	let map = Array.new(11);
+        let charMaps[index] = map;
+
+        let map[0] = a;
+        let map[1] = b;
+        let map[2] = c;
+        let map[3] = d;
+        let map[4] = e;
+        let map[5] = f;
+        let map[6] = g;
+        let map[7] = h;
+        let map[8] = i;
+        let map[9] = j;
+        let map[10] = k;
+
+        return;
+    }
+    
+    // Returns the character map (array of size 11) of the given character.
+    // If the given character is invalid or non-printable, returns the
+    // character map of a black square.
+    function Array getMap(char c) {
+        if ((c < 32) | (c > 126)) {
+            let c = 0;
+        }
+        return charMaps[c];
+    }
+
+    /** Moves the cursor to the j-th column of the i-th row,
+     *  and erases the character displayed there. */
+    function void moveCursor(int i, int j) {
+    }
+
+    /** Displays the given character at the cursor location,
+     *  and advances the cursor one column forward. */
+    function void printChar(char c) {
+    }
+
+    /** displays the given string starting at the cursor location,
+     *  and advances the cursor appropriately. */
+    function void printString(String s) {
+    }
+
+    /** Displays the given integer starting at the cursor location,
+     *  and advances the cursor appropriately. */
+    function void printInt(int i) {
+    }
+
+    /** Advances the cursor to the beginning of the next line. */
+    function void println() {
+    }
+
+    /** Moves the cursor one column back. */
+    function void backSpace() {
+    }
+}
diff --git a/projects/12/OutputTest/Main.jack b/projects/12/OutputTest/Main.jack
new file mode 100644
index 0000000..f243068
--- /dev/null
+++ b/projects/12/OutputTest/Main.jack
@@ -0,0 +1,42 @@
+// 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/12/OutputTest/Main.jack
+
+/** Test program for the OS Output class. */
+class Main {
+
+    /** Outputs the entire character set to the screen using all the
+     *  methods of the Output class. */
+    function void main() {
+        var String s;
+    
+    	let s = String.new(1);
+    	do s.appendChar(String.doubleQuote());
+    
+        do Output.moveCursor(0, 63);
+        do Output.printChar(66);
+        do Output.moveCursor(22, 0);
+        do Output.printChar(67);
+        do Output.moveCursor(22, 63);
+        do Output.printChar(68);
+        do Output.printChar(65);
+        
+        do Output.moveCursor(2, 0);
+        do Output.printString("0123456789");
+        do Output.println();
+        
+        do Output.printString("ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz");
+        do Output.println();
+        
+        do Output.printString("!#$%&'()*+,-./:;<=>?@[\]^_`{|}~");
+        do Output.printString(s);
+        do Output.println();
+        
+        do Output.printInt(-12345);
+        do Output.backSpace();
+        do Output.printInt(6789);
+        
+        return;
+    }
+}
diff --git a/projects/12/OutputTest/OutputTestOutput.gif b/projects/12/OutputTest/OutputTestOutput.gif
new file mode 100644
index 0000000..b8ec2c0
Binary files /dev/null and b/projects/12/OutputTest/OutputTestOutput.gif differ
diff --git a/projects/12/Screen.jack b/projects/12/Screen.jack
new file mode 100644
index 0000000..7356d35
--- /dev/null
+++ b/projects/12/Screen.jack
@@ -0,0 +1,43 @@
+// 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/12/Screen.jack
+
+/**
+ * A library of functions for displaying graphics on the screen.
+ * The Hack physical screen consists of 512 rows (indexed 0..511, top to bottom)
+ * of 256 pixels each (indexed 0..255, left to right). The top left pixel on 
+ * the screen is indexed (0,0).
+ */
+class Screen {
+
+    /** Initializes the Screen. */
+    function void init() {
+    }
+
+    /** Erases the entire screen. */
+    function void clearScreen() {
+    }
+
+    /** Sets the current color, to be used for all subsequent drawXXX commands.
+     *  Black is represented by true, white by false. */
+    function void setColor(boolean b) {
+    }
+
+    /** Draws the (x,y) pixel, using the current color. */
+    function void drawPixel(int x, int y) {
+    }
+
+    /** Draws a line from pixel (x1,y1) to pixel (x2,y2), using the current color. */
+    function void drawLine(int x1, int y1, int x2, int y2) {
+    }
+
+    /** Draws a filled rectangle whose top left corner is (x1, y1)
+     * and bottom right corner is (x2,y2), using the current color. */
+    function void drawRectangle(int x1, int y1, int x2, int y2) {
+    }
+
+    /** Draws a filled circle of radius r<=181 around (x,y), using the current color. */
+    function void drawCircle(int x, int y, int r) {
+    }
+}
diff --git a/projects/12/ScreenTest/Main.jack b/projects/12/ScreenTest/Main.jack
new file mode 100644
index 0000000..00f36bd
--- /dev/null
+++ b/projects/12/ScreenTest/Main.jack
@@ -0,0 +1,36 @@
+// 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/12/ScreenTest/Main.jack
+
+/** Test program for the OS Screen class. */
+class Main {
+
+    /** Draws a sample pictue on the screen using lines and circles. */
+    function void main() {
+    
+        do Screen.drawLine(0,220,511,220);        // base line
+        do Screen.drawRectangle(280,90,410,220);  // house
+        
+        do Screen.setColor(false); 
+        do Screen.drawRectangle(350,120,390,219); // door
+        do Screen.drawRectangle(292,120,332,150); // window
+        
+        do Screen.setColor(true); 
+        do Screen.drawCircle(360,170,3);          // door handle
+        do Screen.drawLine(280,90,345,35);        // roof
+        do Screen.drawLine(345,35,410,90);        // roof
+
+        do Screen.drawCircle(140,60,30);          // sun
+        do Screen.drawLine(140,26, 140, 6);       
+        do Screen.drawLine(163,35,178,20);       
+        do Screen.drawLine(174,60,194,60);       
+        do Screen.drawLine(163,85,178,100);       
+        do Screen.drawLine(140,94,140,114);       
+        do Screen.drawLine(117,85,102,100);       
+        do Screen.drawLine(106,60,86,60);       
+        do Screen.drawLine(117,35,102,20);       
+        
+        return;
+    }
+}
diff --git a/projects/12/ScreenTest/ScreenTestOutput.gif b/projects/12/ScreenTest/ScreenTestOutput.gif
new file mode 100644
index 0000000..f1742cc
Binary files /dev/null and b/projects/12/ScreenTest/ScreenTestOutput.gif differ
diff --git a/projects/12/String.jack b/projects/12/String.jack
new file mode 100644
index 0000000..228d71c
--- /dev/null
+++ b/projects/12/String.jack
@@ -0,0 +1,64 @@
+// 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/12/String.jack
+
+/**
+ * Represents character strings. In addition for constructing and disposing
+ * strings, the class features methods for getting and setting individual
+ * characters of the string, for erasing the string's last character,
+ * for appending a character to the string's end, and more typical
+ * string-oriented operations.
+ */
+class String {
+
+    /** constructs a new empty string with a maximum length of maxLength
+     *  and initial length of 0. */
+    constructor String new(int maxLength) {
+    }
+
+    /** Disposes this string. */
+    method void dispose() {
+    }
+
+    /** Returns the current length of this string. */
+    method int length() {
+    }
+
+    /** Returns the character at the j-th location of this string. */
+    method char charAt(int j) {
+    }
+
+    /** Sets the character at the j-th location of this string to c. */
+    method void setCharAt(int j, char c) {
+    }
+
+    /** Appends c to this string's end and returns this string. */
+    method String appendChar(char c) {
+    }
+
+    /** Erases the last character from this string. */
+    method void eraseLastChar() {
+    }
+
+    /** Returns the integer value of this string, 
+     *  until a non-digit character is detected. */
+    method int intValue() {
+    }
+
+    /** Sets this string to hold a representation of the given value. */
+    method void setInt(int val) {
+    }
+
+    /** Returns the new line character. */
+    function char newLine() {
+    }
+
+    /** Returns the backspace character. */
+    function char backSpace() {
+    }
+
+    /** Returns the double quote (") character. */
+    function char doubleQuote() {
+    }
+}
diff --git a/projects/12/StringTest/Main.jack b/projects/12/StringTest/Main.jack
new file mode 100644
index 0000000..2848548
--- /dev/null
+++ b/projects/12/StringTest/Main.jack
@@ -0,0 +1,83 @@
+// 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/12/StringTest/Main.jack
+
+/** Test program for the OS String class. */
+class Main {
+
+    /** Performs various string manipulations and displays their results. */
+    function void main() {
+        var String s;
+        var String i;
+        
+        let s = String.new(0); // a zero-capacity string should be supported
+        do s.dispose();
+
+        let s = String.new(6); // capacity 6, make sure that length 5 is displayed
+        let s = s.appendChar(97);
+        let s = s.appendChar(98);
+        let s = s.appendChar(99);
+        let s = s.appendChar(100);
+        let s = s.appendChar(101);
+        do Output.printString("new,appendChar: ");
+        do Output.printString(s);                // new, appendChar: abcde
+        do Output.println();
+    
+        let i = String.new(6);
+        do i.setInt(12345);
+        do Output.printString("setInt: ");
+        do Output.printString(i);                // setInt: 12345
+        do Output.println();
+
+        do i.setInt(-32767);
+        do Output.printString("setInt: ");
+        do Output.printString(i);                // setInt: -32767
+        do Output.println();
+        
+        do Output.printString("length: ");
+        do Output.printInt(s.length());          // length: 5
+        do Output.println();
+        
+        do Output.printString("charAt[2]: ");
+        do Output.printInt(s.charAt(2));         // charAt[2]: 99
+        do Output.println();
+        
+        do s.setCharAt(2, 45);
+        do Output.printString("setCharAt(2,'-'): ");     
+        do Output.printString(s);                // setCharAt(2,'-'): ab-de
+        do Output.println();
+        
+        do s.eraseLastChar();        
+        do Output.printString("eraseLastChar: ");     
+        do Output.printString(s);                // eraseLastChar: ab-d
+        do Output.println();
+        
+        let s = "456";
+        do Output.printString("intValue: ");
+        do Output.printInt(s.intValue());        // intValue: 456
+        do Output.println();
+        
+        let s = "-32123";
+        do Output.printString("intValue: ");
+        do Output.printInt(s.intValue());        // intValue: -32123
+        do Output.println();
+        
+        do Output.printString("backSpace: ");
+        do Output.printInt(String.backSpace());  // backSpace: 129
+        do Output.println();
+        
+        do Output.printString("doubleQuote: ");
+        do Output.printInt(String.doubleQuote());// doubleQuote: 34
+        do Output.println();
+        
+        do Output.printString("newLine: ");
+        do Output.printInt(String.newLine());    // newLine: 128
+        do Output.println();
+        
+        do i.dispose();
+        do s.dispose();
+
+        return;
+    }
+}
diff --git a/projects/12/StringTest/StringTestOutput.gif b/projects/12/StringTest/StringTestOutput.gif
new file mode 100644
index 0000000..5c2932c
Binary files /dev/null and b/projects/12/StringTest/StringTestOutput.gif differ
diff --git a/projects/12/Sys.jack b/projects/12/Sys.jack
new file mode 100644
index 0000000..bee6f67
--- /dev/null
+++ b/projects/12/Sys.jack
@@ -0,0 +1,27 @@
+// 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/12/Sys.jack
+
+/**
+ * A library that supports various program execution services.
+ */
+class Sys {
+
+    /** Performs all the initializations required by the OS. */
+    function void init() {
+    }
+
+    /** Halts the program execution. */
+    function void halt() {
+    }
+
+    /** Waits approximately duration milliseconds and returns.  */
+    function void wait(int duration) {
+    }
+
+    /** Displays the given error code in the form "ERR<errorCode>",
+     *  and halts the program's execution. */
+    function void error(int errorCode) {
+    }
+}
diff --git a/projects/12/SysTest/Main.jack b/projects/12/SysTest/Main.jack
new file mode 100644
index 0000000..a153b25
--- /dev/null
+++ b/projects/12/SysTest/Main.jack
@@ -0,0 +1,31 @@
+// 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/12/SysTest/Main.jack
+
+/** Test program for the OS Sys class. */
+class Main {
+
+    /** Tests the wait method of the Sys class. */
+    function void main() {
+        var char key;
+
+        do Output.printString("Wait test:");
+        do Output.println();
+        do Output.printString("Press any key. After 2 seconds, another message will be printed:");
+
+        while (key = 0) {
+	        let key = Keyboard.keyPressed();
+        }
+        while (~(key = 0)) {
+            let key = Keyboard.keyPressed();
+        }
+        
+        do Sys.wait(2000);
+
+        do Output.println();
+        do Output.printString("Time is up. Make sure that 2 seconds elapsed.");
+        
+        return;
+    }
+}
-- 
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