Add ast_expression_bin subclass of ast_expression

The ast_expression_bin subclass is used for all binary expressions
such as addition, subtraction, and comparisons.  Several other
subclasses are soon to follow.
diff --git a/ast_expr.cpp b/ast_expr.cpp
new file mode 100644
index 0000000..ad29cdc
--- /dev/null
+++ b/ast_expr.cpp
@@ -0,0 +1,92 @@
+/*
+ * Copyright © 2010 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+#include <cstdio>
+#include <cassert>
+#include "ast.h"
+
+const char *
+ast_expression::operator_string(enum ast_operators op)
+{
+   static const char *const operators[] = {
+      "=",
+      "+",
+      "-",
+      "+",
+      "-",
+      "*",
+      "/",
+      "%",
+      "<<",
+      ">>",
+      "<",
+      ">",
+      "<=",
+      ">=",
+      "==",
+      "!=",
+      "&",
+      "^",
+      "|",
+      "~",
+      "&&",
+      "^^",
+      "!",
+
+      "*=",
+      "/=",
+      "%=",
+      "+=",
+      "-=",
+      "<<=",
+      ">>=",
+      "&=",
+      "^=",
+      "|=",
+
+      "?:",
+      "++",
+      "--",
+      "++",
+      "--",
+      ".",
+   };
+
+   return operators[op];
+}
+
+
+ast_expression_bin::ast_expression_bin(int oper, ast_expression *ex0,
+				       ast_expression *ex1) :
+   ast_expression(oper, ex0, ex1, NULL)
+{
+   assert((oper >= ast_plus) && (oper <= ast_logic_not));
+}
+
+
+void
+ast_expression_bin::print(void) const
+{
+   subexpressions[0]->print();
+   printf("%s ", operator_string(oper));
+   subexpressions[1]->print();
+}