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+// -*- mode: C++ -*-
+
+// Copyright (c) 2010 Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// postfix_evaluator.h: Postfix (reverse Polish) notation expression evaluator.
+//
+// PostfixEvaluator evaluates an expression, using the expression itself
+// in postfix (reverse Polish) notation and a dictionary mapping constants
+// and variables to their values.  The evaluator supports standard
+// arithmetic operations, assignment into variables, and when an optional
+// MemoryRange is provided, dereferencing.  (Any unary key-to-value operation
+// may be used with a MemoryRange implementation that returns the appropriate
+// values, but PostfixEvaluator was written with dereferencing in mind.)
+//
+// The expression language is simple.  Expressions are supplied as strings,
+// with operands and operators delimited by whitespace.  Operands may be
+// either literal values suitable for ValueType, or constants or variables,
+// which reference the dictionary.  The supported binary operators are +
+// (addition), - (subtraction), * (multiplication), / (quotient of division),
+// % (modulus of division), and @ (data alignment). The alignment operator (@)
+// accepts a value and an alignment size, and produces a result that is a
+// multiple of the alignment size by truncating the input value.
+// The unary ^ (dereference) operator is also provided.  These operators
+// allow any operand to be either a literal value, constant, or variable.
+// Assignment (=) of any type of operand into a variable is also supported.
+//
+// The dictionary is provided as a map with string keys.  Keys beginning
+// with the '$' character are treated as variables.  All other keys are
+// treated as constants.  Any results must be assigned into variables in the
+// dictionary.  These variables do not need to exist prior to calling
+// Evaluate, unless used in an expression prior to being assigned to.  The
+// internal stack state is not made available after evaluation, and any
+// values remaining on the stack are treated as evidence of incomplete
+// execution and cause the evaluator to indicate failure.
+//
+// PostfixEvaluator is intended to support evaluation of "program strings"
+// obtained from MSVC frame data debugging information in pdb files as
+// returned by the DIA APIs.
+//
+// Author: Mark Mentovai
+
+#ifndef PROCESSOR_POSTFIX_EVALUATOR_H__
+#define PROCESSOR_POSTFIX_EVALUATOR_H__
+
+
+#include <map>
+#include <string>
+#include <vector>
+
+#include "common/using_std_string.h"
+
+namespace google_breakpad {
+
+using std::map;
+using std::vector;
+
+class MemoryRegion;
+
+template<typename ValueType>
+class PostfixEvaluator {
+ public:
+  typedef map<string, ValueType> DictionaryType;
+  typedef map<string, bool> DictionaryValidityType;
+
+  // Create a PostfixEvaluator object that may be used (with Evaluate) on
+  // one or more expressions.  PostfixEvaluator does not take ownership of
+  // either argument.  |memory| may be NULL, in which case dereferencing
+  // (^) will not be supported.  |dictionary| may be NULL, but evaluation
+  // will fail in that case unless set_dictionary is used before calling
+  // Evaluate.
+  PostfixEvaluator(DictionaryType *dictionary, const MemoryRegion *memory)
+      : dictionary_(dictionary), memory_(memory), stack_() {}
+
+  // Evaluate the expression, starting with an empty stack. The results of
+  // execution will be stored in one (or more) variables in the dictionary.
+  // Returns false if any failures occur during execution, leaving
+  // variables in the dictionary in an indeterminate state. If assigned is
+  // non-NULL, any keys set in the dictionary as a result of evaluation
+  // will also be set to true in assigned, providing a way to determine if
+  // an expression modifies any of its input variables.
+  bool Evaluate(const string &expression, DictionaryValidityType *assigned);
+
+  // Like Evaluate, but provides the value left on the stack to the
+  // caller. If evaluation succeeds and leaves exactly one value on
+  // the stack, pop that value, store it in *result, and return true.
+  // Otherwise, return false.
+  bool EvaluateForValue(const string &expression, ValueType *result);
+
+  DictionaryType* dictionary() const { return dictionary_; }
+
+  // Reset the dictionary.  PostfixEvaluator does not take ownership.
+  void set_dictionary(DictionaryType *dictionary) {dictionary_ = dictionary; }
+
+ private:
+  // Return values for PopValueOrIdentifier
+  enum PopResult {
+    POP_RESULT_FAIL = 0,
+    POP_RESULT_VALUE,
+    POP_RESULT_IDENTIFIER
+  };
+
+  // Retrieves the topmost literal value, constant, or variable from the
+  // stack.  Returns POP_RESULT_VALUE if the topmost entry is a literal
+  // value, and sets |value| accordingly.  Returns POP_RESULT_IDENTIFIER
+  // if the topmost entry is a constant or variable identifier, and sets
+  // |identifier| accordingly.  Returns POP_RESULT_FAIL on failure, such
+  // as when the stack is empty.
+  PopResult PopValueOrIdentifier(ValueType *value, string *identifier);
+
+  // Retrieves the topmost value on the stack.  If the topmost entry is
+  // an identifier, the dictionary is queried for the identifier's value.
+  // Returns false on failure, such as when the stack is empty or when
+  // a nonexistent identifier is named.
+  bool PopValue(ValueType *value);
+
+  // Retrieves the top two values on the stack, in the style of PopValue.
+  // value2 is popped before value1, so that value1 corresponds to the
+  // entry that was pushed prior to value2.  Returns false on failure.
+  bool PopValues(ValueType *value1, ValueType *value2);
+
+  // Pushes a new value onto the stack.
+  void PushValue(const ValueType &value);
+
+  // Evaluate expression, updating *assigned if it is non-zero. Return
+  // true if evaluation completes successfully. Do not clear the stack
+  // upon successful evaluation.
+  bool EvaluateInternal(const string &expression,
+                        DictionaryValidityType *assigned);
+
+  bool EvaluateToken(const string &token,
+                     const string &expression,
+                     DictionaryValidityType *assigned);
+
+  // The dictionary mapping constant and variable identifiers (strings) to
+  // values.  Keys beginning with '$' are treated as variable names, and
+  // PostfixEvaluator is free to create and modify these keys.  Weak pointer.
+  DictionaryType *dictionary_;
+
+  // If non-NULL, the MemoryRegion used for dereference (^) operations.
+  // If NULL, dereferencing is unsupported and will fail.  Weak pointer.
+  const MemoryRegion *memory_;
+
+  // The stack contains state information as execution progresses.  Values
+  // are pushed on to it as the expression string is read and as operations
+  // yield values; values are popped when used as operands to operators.
+  vector<string> stack_;
+};
+
+}  // namespace google_breakpad
+
+
+#endif  // PROCESSOR_POSTFIX_EVALUATOR_H__