init: init nachos hw01

c++example/list.cc

@@ -0,0 +1,133 @@
+// list.cc 
+//     	Routines to manage a singly-linked list of integers. 
+//
+// 	A "ListElement" is allocated for each item to be put on the
+//	list; it is de-allocated when the item is removed. This means
+//      we don't need to keep a "next" pointer in every object we
+//      want to put on a list.
+// 
+// Copyright (c) 1992,1993,1995 The Regents of the University of California.
+// All rights reserved.  See copyright.h for copyright notice and limitation 
+// of liability and disclaimer of warranty provisions.
+
+
+extern "C" {
+#include <assert.h>
+
+#define ASSERT(expression)  assert(expression)
+}
+
+#include "copyright.h"
+#include "list.h"
+
+const int NULL = 0;
+
+
+// The following class defines a "list element" -- which is
+// used to keep track of one item on a list.  It is equivalent to a
+// LISP cell, with a "car" ("next") pointing to the next element on the list,
+// and a "cdr" ("item") containing the item on the list.
+//
+// Class defined in list.cc, because only the List class can be allocating
+// and accessing ListElements.
+
+class ListElement {
+   public:
+     ListElement(int value) { item = value; next = NULL;};
+     					// constructor for list element
+
+     ListElement *next;		// next element on list, 
+				// NULL if this is the last
+     int item; 	    	        // value of this element
+};
+
+
+
+//----------------------------------------------------------------------
+// List::List
+//	Initialize a list, empty to start with.
+//	Elements can now be added to the list.
+//----------------------------------------------------------------------
+
+List::List() { 
+
+    first = last = NULL; 
+}
+
+
+//----------------------------------------------------------------------
+// List::~List
+//	Prepare a list for deallocation.  If the list still contains any 
+//	ListElements, de-allocate them.
+//----------------------------------------------------------------------
+
+List::~List() { 
+   
+    while (!Empty())
+	(void) Remove();	 // delete all the list elements
+}
+
+
+//----------------------------------------------------------------------
+// List::Prepend
+//      Put an integer on the front of the list.
+//      
+//	Allocate a ListElement to keep track of the integer.
+//      If the list is empty, then this will be the only element.
+//	Otherwise, put it at the beginning.
+//
+//	"value" is the integer to be put on the list.
+//----------------------------------------------------------------------
+
+void
+List::Prepend(int value) {
+    ListElement *element = new ListElement(value);
+
+    if (Empty()) {		// list is empty
+	first = element;
+	last = element;
+    } else {			// else put it before first
+	element->next = first;
+	first = element;
+    }
+}
+
+//----------------------------------------------------------------------
+// List::Remove
+//      Remove the first integer from the front of the list.
+//	Error if nothing on the list.
+// 
+// Returns:
+//	The removed integer.
+//----------------------------------------------------------------------
+
+int
+List::Remove() {
+    ListElement *element = first;
+    int value;
+
+    ASSERT(!Empty());
+
+    element = first;
+    value = first->item;
+
+    if (first == last) {	// list had one item, now has none 
+        first = NULL;
+	last = NULL;
+    } else {
+        first = element->next;
+    }
+
+    delete element;		// deallocate list element -- no longer needed
+    return value;
+}
+
+//----------------------------------------------------------------------
+// List::Empty
+//      Returns TRUE if the list is empty (has no items).
+//----------------------------------------------------------------------
+
+bool
+List::Empty() { 
+    return (first == NULL);
+}