1 files changed, 84 insertions, 0 deletions
diff --git a/projects/12/MemoryTest/Memory.jack b/projects/12/MemoryTest/Memory.jack
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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/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 {
+    static Array memory;
+    static Array heap;
+    static int first;
+
+    /** Initializes the class. */
+    function void init() {
+        let memory = 0;
+        let heap = 2048;
+        let heap[0] = -1;
+        let heap[1] = 14334;
+        return;
+    }
+
+    /** Returns the RAM value at the given address. */
+    function int peek(int address) {
+        return memory[address];
+    }
+
+    /** Sets the RAM value at the given address to the given value. */
+    function void poke(int address, int value) {
+        let memory[address] = value;
+        return;
+    }
+
+    /** Finds an available RAM block of the given size and returns
+     *  a reference to its base address. */
+    function int alloc(int size) {
+        var int current;
+        var int size2;
+        var int newLast;
+        let current = 0;
+        let size2 = size + 2;
+        while ((current > -1) & (heap[current + 1] < size2)) {
+            let current = heap[current];
+        }
+        if (current = -1) {
+            do String.println("Insufficient space for allocation!");
+            do Sys.error(1);
+            return -1;
+        } else {
+            let heap[current + 1] = heap[current + 1] - size2;
+            let newLast = current + heap[current + 1] + 2;
+            let heap[newLast] = heap[current];
+            let heap[current] = newLast;
+            let heap[newLast + 1] = size;
+            return heap + newLast + 2;
+        }
+    }
+
+    /** De-allocates the given object (cast as an array) by making
+     *  it available for future allocations. */
+    function void deAlloc(Array o) {
+        var int oBase;
+        var int current;
+        var int prev;
+        let prev = 0;
+        let current = heap[prev];
+        let oBase = o - heap - 2;
+        while ((current > -1) & (~(current = oBase))){
+            let prev = current;
+            let current = heap[current];
+        }
+        if (current = -1) {
+            do String.println("The impossible happened");
+            do Sys.error(1);
+            return;
+        } else {
+            let heap[prev] = heap[current];
+            let heap[prev + 1] = heap[prev] - prev - 2;
+            return;
+        }
+    }    
+}