--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jaxp/src/com/sun/java_cup/internal/runtime/virtual_parse_stack.java Thu Apr 12 08:38:26 2012 -0700
@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+
+package com.sun.java_cup.internal.runtime;
+
+import java.util.Stack;
+
+/** This class implements a temporary or "virtual" parse stack that
+ * replaces the top portion of the actual parse stack (the part that
+ * has been changed by some set of operations) while maintaining its
+ * original contents. This data structure is used when the parse needs
+ * to "parse ahead" to determine if a given error recovery attempt will
+ * allow the parse to continue far enough to consider it successful. Once
+ * success or failure of parse ahead is determined the system then
+ * reverts to the original parse stack (which has not actually been
+ * modified). Since parse ahead does not execute actions, only parse
+ * state is maintained on the virtual stack, not full Symbol objects.
+ *
+ * @see com.sun.java_cup.internal.runtime.lr_parser
+ * @author Frank Flannery
+ */
+
+public class virtual_parse_stack {
+ /*-----------------------------------------------------------*/
+ /*--- Constructor(s) ----------------------------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** Constructor to build a virtual stack out of a real stack. */
+ public virtual_parse_stack(Stack shadowing_stack) throws java.lang.Exception
+ {
+ /* sanity check */
+ if (shadowing_stack == null)
+ throw new Exception(
+ "Internal parser error: attempt to create null virtual stack");
+
+ /* set up our internals */
+ real_stack = shadowing_stack;
+ vstack = new Stack();
+ real_next = 0;
+
+ /* get one element onto the virtual portion of the stack */
+ get_from_real();
+ }
+
+ /*-----------------------------------------------------------*/
+ /*--- (Access to) Instance Variables ------------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** The real stack that we shadow. This is accessed when we move off
+ * the bottom of the virtual portion of the stack, but is always left
+ * unmodified.
+ */
+ protected Stack real_stack;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Top of stack indicator for where we leave off in the real stack.
+ * This is measured from top of stack, so 0 would indicate that no
+ * elements have been "moved" from the real to virtual stack.
+ */
+ protected int real_next;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The virtual top portion of the stack. This stack contains Integer
+ * objects with state numbers. This stack shadows the top portion
+ * of the real stack within the area that has been modified (via operations
+ * on the virtual stack). When this portion of the stack becomes empty we
+ * transfer elements from the underlying stack onto this stack.
+ */
+ protected Stack vstack;
+
+ /*-----------------------------------------------------------*/
+ /*--- General Methods ---------------------------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** Transfer an element from the real to the virtual stack. This assumes
+ * that the virtual stack is currently empty.
+ */
+ protected void get_from_real()
+ {
+ Symbol stack_sym;
+
+ /* don't transfer if the real stack is empty */
+ if (real_next >= real_stack.size()) return;
+
+ /* get a copy of the first Symbol we have not transfered */
+ stack_sym = (Symbol)real_stack.elementAt(real_stack.size()-1-real_next);
+
+ /* record the transfer */
+ real_next++;
+
+ /* put the state number from the Symbol onto the virtual stack */
+ vstack.push(new Integer(stack_sym.parse_state));
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Indicate whether the stack is empty. */
+ public boolean empty()
+ {
+ /* if vstack is empty then we were unable to transfer onto it and
+ the whole thing is empty. */
+ return vstack.empty();
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Return value on the top of the stack (without popping it). */
+ public int top() throws java.lang.Exception
+ {
+ if (vstack.empty())
+ throw new Exception(
+ "Internal parser error: top() called on empty virtual stack");
+
+ return ((Integer)vstack.peek()).intValue();
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Pop the stack. */
+ public void pop() throws java.lang.Exception
+ {
+ if (vstack.empty())
+ throw new Exception(
+ "Internal parser error: pop from empty virtual stack");
+
+ /* pop it */
+ vstack.pop();
+
+ /* if we are now empty transfer an element (if there is one) */
+ if (vstack.empty())
+ get_from_real();
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Push a state number onto the stack. */
+ public void push(int state_num)
+ {
+ vstack.push(new Integer(state_num));
+ }
+
+ /*-----------------------------------------------------------*/
+
+}