# HG changeset patch
# User Manuele Conti <conti.ma@alice.it>
# Date 1338916649 -7200
# Node ID dabffc3086dce81eb0209e96dbc06b14ebb50d36
# Parent  61410284a9b46b2b3e437af2eaa39f5b1f6882a7
Start constant_folding class.

diff -r 61410284a9b4 -r dabffc3086dc absyntax/absyntax.cc
--- a/absyntax/absyntax.cc	Tue Jun 05 11:10:12 2012 +0200
+++ b/absyntax/absyntax.cc	Tue Jun 05 19:17:29 2012 +0200
@@ -62,6 +62,10 @@
   this->last_column  = last_column;
   this->last_order   = last_order;
   this->datatype     = NULL;
+  this->const_value_real     = NULL;
+  this->const_value_integer  = NULL;
+  this->const_value_uinteger = NULL;
+  this->const_value_bool     = NULL;
 }
 
 
diff -r 61410284a9b4 -r dabffc3086dc absyntax/absyntax.hh
--- a/absyntax/absyntax.hh	Tue Jun 05 11:10:12 2012 +0200
+++ b/absyntax/absyntax.hh	Tue Jun 05 19:17:29 2012 +0200
@@ -48,9 +48,10 @@
 
 #include <stdio.h> // required for NULL
 #include <vector>
+#include <string>
 
 /* Forward declaration of the visitor interface
- * dclared in the visitor.hh file
+ * declared in the visitor.hh file
  * We cannot include the visitor.hh file, as it will
  * include this same file first, as it too requires references
  * to the abstract syntax classes defined here.
@@ -61,7 +62,6 @@
 class symbol_c; // forward declaration
 
 
-
 /* The base class of all symbols */
 class symbol_c {
 
@@ -83,7 +83,12 @@
      * If it points to an object of type invalid_type_name_c, it means it is invalid.
      * Otherwise, it points to an object of the apropriate data type (e.g. int_type_name_c, bool_type_name_c, ...)
      */
-    symbol_c *datatype;    
+    symbol_c *datatype;
+
+    double   *const_value_real;
+    int64_t  *const_value_integer;
+    uint64_t *const_value_uinteger;
+    bool     *const_value_bool;
 
 
   public:
@@ -302,6 +307,4 @@
 #undef SYM_REF5
 #undef SYM_REF6
 
-
-
 #endif /*  _ABSYNTAX_HH */
diff -r 61410284a9b4 -r dabffc3086dc absyntax_utils/absyntax_utils.cc
--- a/absyntax_utils/absyntax_utils.cc	Tue Jun 05 11:10:12 2012 +0200
+++ b/absyntax_utils/absyntax_utils.cc	Tue Jun 05 19:17:29 2012 +0200
@@ -52,6 +52,7 @@
 #include <strings.h>
 #include <string.h>  /* required for strlen() */
 #include <stdlib.h>  /* required for atoi() */
+#include <errno.h>   /* required for errno */
 
 #include "../util/symtable.hh"
 #include "../util/dsymtable.hh"
@@ -115,6 +116,22 @@
   return atoll(str.c_str());
 }
 
+uint64_t extract_hex_value(symbol_c *sym) {
+	std::string str = "";
+	char *endptr;
+	hex_integer_c * hex_integer;
+	uint64_t ret;
+
+    if ((hex_integer = dynamic_cast<hex_integer_c *>(sym)) == NULL) ERROR;
+    for(unsigned int i = 3; i < strlen(hex_integer->value); i++)
+    	if (hex_integer->value[i] != '_') str += hex_integer->value[i];
+    errno = 0;    /* To distinguish success/failure after call */
+    ret = strtol(str.c_str(), &endptr, 16);
+    if (errno != 0) ERROR;
+
+	return ret;
+}
+
 
 
 /***********************************************************************/
diff -r 61410284a9b4 -r dabffc3086dc absyntax_utils/absyntax_utils.hh
--- a/absyntax_utils/absyntax_utils.hh	Tue Jun 05 11:10:12 2012 +0200
+++ b/absyntax_utils/absyntax_utils.hh	Tue Jun 05 19:17:29 2012 +0200
@@ -57,6 +57,8 @@
 
 /* extract the value of an integer from an integer_c object !! */
 long long extract_integer_value(symbol_c *integer);
+
+uint64_t extract_hex_value(symbol_c *sym);
   
 /* A symbol table with all globally declared functions... */
 extern function_declaration_c null_symbol1;
diff -r 61410284a9b4 -r dabffc3086dc stage3/Makefile.am
--- a/stage3/Makefile.am	Tue Jun 05 11:10:12 2012 +0200
+++ b/stage3/Makefile.am	Tue Jun 05 19:17:29 2012 +0200
@@ -10,5 +10,6 @@
 	print_datatypes_error.cc \
 	datatype_functions.cc \
 	lvalue_check.cc \
-	array_range_check.cc
+	array_range_check.cc \
+        constant_folding.cc
 
diff -r 61410284a9b4 -r dabffc3086dc stage3/constant_folding.cc
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/stage3/constant_folding.cc	Tue Jun 05 19:17:29 2012 +0200
@@ -0,0 +1,494 @@
+/*
+ *  matiec - a compiler for the programming languages defined in IEC 61131-3
+ *
+ *  Copyright (C) 2003-2011  Mario de Sousa (msousa@fe.up.pt)
+ *  Copyright (C) 2012       Manuele Conti (conti.ma@alice.it)
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ * This code is made available on the understanding that it will not be
+ * used in safety-critical situations without a full and competent review.
+ */
+
+/*
+ * An IEC 61131-3 compiler.
+ *
+ * Based on the
+ * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
+ *
+ */
+
+
+/* Determine the value of an ST expression.
+ * Filling in all symbols the correct value.
+ *
+ * For example:
+ *       2 + 3         -> returns constant_value_integer = 5
+ *       22.2 - 5.0    -> returns constant_value_real    = 17.2
+ *       etc...
+ */
+
+#include "constant_folding.hh"
+#include <typeinfo>
+#include <limits>
+#include <math.h> /* required for pow function */
+
+#define FIRST_(symbol1, symbol2) (((symbol1)->first_order < (symbol2)->first_order)   ? (symbol1) : (symbol2))
+#define  LAST_(symbol1, symbol2) (((symbol1)->last_order  > (symbol2)->last_order)    ? (symbol1) : (symbol2))
+
+#define STAGE3_ERROR(error_level, symbol1, symbol2, ...) {                                                                  \
+  if (current_display_error_level >= error_level) {                                                                         \
+    fprintf(stderr, "%s:%d-%d..%d-%d: error: ",                                                                             \
+            FIRST_(symbol1,symbol2)->first_file, FIRST_(symbol1,symbol2)->first_line, FIRST_(symbol1,symbol2)->first_column,\
+                                                 LAST_(symbol1,symbol2) ->last_line,  LAST_(symbol1,symbol2) ->last_column);\
+    fprintf(stderr, __VA_ARGS__);                                                                                           \
+    fprintf(stderr, "\n");                                                                                                  \
+    error_count++;                                                                                                     \
+  }                                                                                                                         \
+}
+
+
+#define STAGE3_WARNING(symbol1, symbol2, ...) {                                                                             \
+    fprintf(stderr, "%s:%d-%d..%d-%d: warning: ",                                                                           \
+            FIRST_(symbol1,symbol2)->first_file, FIRST_(symbol1,symbol2)->first_line, FIRST_(symbol1,symbol2)->first_column,\
+                                                 LAST_(symbol1,symbol2) ->last_line,  LAST_(symbol1,symbol2) ->last_column);\
+    fprintf(stderr, __VA_ARGS__);                                                                                           \
+    fprintf(stderr, "\n");                                                                                                  \
+    warning_found = true;                                                                                                   \
+}
+
+
+
+#define DO_OPER(dtype)\
+    (NULL != symbol->r_exp->const_value_##dtype ) && \
+    (NULL != symbol->l_exp->const_value_##dtype )
+
+
+#define CHECK_OVERFLOW_SUM(a, b, type)\
+	((((std::numeric_limits< type >::max() - a) < (b)) ? 1 : 0) || \
+	 (((std::numeric_limits< type >::min() + a) > (b)) ? 1 : 0))
+
+#define CHECK_OVERFLOW_SUB(a, b, type)\
+	((((std::numeric_limits< type >::max() - a) < (-b)) ? 1 : 0) || \
+	 (((std::numeric_limits< type >::min() + a) > (-b)) ? 1 : 0))
+
+
+
+
+
+constant_folding_c::constant_folding_c(symbol_c *symbol) {
+    error_count = 0;
+    current_display_error_level = 0;
+}
+
+constant_folding_c::~constant_folding_c(void) {
+}
+
+int constant_folding_c::get_error_count() {
+	return error_count;
+}
+
+
+/*********************/
+/* B 1.2 - Constants */
+/*********************/
+/******************************/
+/* B 1.2.1 - Numeric Literals */
+/******************************/
+void *constant_folding_c::visit(real_c *symbol) {
+	double *real_value;
+
+	real_value = (double *)malloc(sizeof(double));
+	sscanf(symbol->value, "%lf", real_value);
+	symbol->const_value_real = real_value;
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(integer_c *symbol) {
+	int64_t *integer_value;
+
+	integer_value = (int64_t *)malloc(sizeof(int64_t));
+	*integer_value = extract_integer_value(symbol);
+	symbol->const_value_integer = integer_value;
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(neg_real_c *symbol) {
+	double *real_value;
+
+	real_value = (double *)malloc(sizeof(double));
+	symbol->exp->accept(*this);
+	if (NULL == symbol->exp->const_value_real)
+		ERROR;
+	*real_value = - *(symbol->exp->const_value_real);
+	symbol->const_value_real = real_value;
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(neg_integer_c *symbol) {
+	int64_t *integer_value;
+
+	integer_value = (int64_t *)malloc(sizeof(int64_t));
+	*integer_value = extract_integer_value(symbol);
+	symbol->const_value_integer = integer_value;
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(binary_integer_c *symbol) {
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(octal_integer_c *symbol) {
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(hex_integer_c *symbol) {
+	int64_t *integer_value;
+
+	integer_value = (int64_t *)malloc(sizeof(int64_t));
+	*integer_value = extract_hex_value(symbol);
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(integer_literal_c *symbol) {
+	int64_t *integer_value;
+
+	symbol->value->accept(*this);
+	if (NULL == symbol->value->const_value_integer) ERROR;
+	*(symbol->const_value_integer) = *(symbol->value->const_value_integer);
+	integer_value = (int64_t *)malloc(sizeof(int64_t));
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(real_literal_c *symbol) {
+	double *real_value;
+
+	real_value = (double *)malloc(sizeof(double));
+	symbol->value->accept(*this);
+	if (NULL == symbol->value->const_value_real)
+		ERROR;
+	*real_value = *(symbol->value->const_value_real);
+	symbol->const_value_real = real_value;
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(bit_string_literal_c *symbol) {
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(boolean_literal_c *symbol) {
+	symbol->value->accept(*this);
+	if (NULL == symbol->value->const_value_bool) ERROR;
+	symbol->const_value_bool = (bool *)malloc(sizeof(bool));
+	*(symbol->const_value_bool) = *(symbol->value->const_value_bool);
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(boolean_true_c *symbol) {
+	symbol->const_value_bool = (bool *)malloc(sizeof(bool));
+	*(symbol->const_value_bool) = true;
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(boolean_false_c *symbol) {
+	symbol->const_value_bool = (bool *)malloc(sizeof(bool));
+	*(symbol->const_value_bool) = false;
+
+	return NULL;
+}
+
+/***************************************/
+/* B.3 - Language ST (Structured Text) */
+/***************************************/
+/***********************/
+/* B 3.1 - Expressions */
+/***********************/
+void *constant_folding_c::visit(or_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(bool)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_bool) || *(symbol->r_exp->const_value_bool);
+	}
+	if (DO_OPER(integer)) {
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_integer) = *(symbol->l_exp->const_value_integer) | *(symbol->r_exp->const_value_integer);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(xor_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) ^ *(symbol->r_exp->const_value_integer);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(and_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(bool)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_bool) && *(symbol->r_exp->const_value_bool);
+	}
+	if (DO_OPER(integer)) {
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) & *(symbol->r_exp->const_value_integer);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(equ_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(bool)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_bool) == *(symbol->r_exp->const_value_bool);
+	}
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) == *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_real) == *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(notequ_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(bool)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_bool) != *(symbol->r_exp->const_value_bool);
+	}
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) != *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_real) != *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(lt_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) < *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_real) < *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(gt_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) > *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_real) > *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(le_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) <= *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_real) <= *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(ge_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_integer) >= *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = *(symbol->l_exp->const_value_real) >= *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(add_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		if (CHECK_OVERFLOW_SUM(*(symbol->l_exp->const_value_integer), *(symbol->r_exp->const_value_integer), int64_t))
+			STAGE3_ERROR(0, symbol, symbol, "Overflow in constant expression.");
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_integer) = *(symbol->l_exp->const_value_integer) + *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		if (CHECK_OVERFLOW_SUM(*(symbol->l_exp->const_value_real), *(symbol->r_exp->const_value_real), double))
+			STAGE3_ERROR(0, symbol, symbol, "Overflow in constant expression.");
+		symbol->const_value_real = (double*) malloc(sizeof(double));
+		*(symbol->const_value_real) = *(symbol->l_exp->const_value_real) + *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(sub_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		if (CHECK_OVERFLOW_SUB(*(symbol->l_exp->const_value_integer), *(symbol->r_exp->const_value_integer), int64_t))
+			STAGE3_ERROR(0, symbol, symbol, "Overflow in constant expression.");
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_integer) = *(symbol->l_exp->const_value_integer) - *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		if (CHECK_OVERFLOW_SUB(*(symbol->l_exp->const_value_real), *(symbol->r_exp->const_value_real), double))
+			STAGE3_ERROR(0, symbol, symbol, "Overflow in constant expression.");
+		symbol->const_value_real = (double*) malloc(sizeof(double));
+		*(symbol->const_value_real) = *(symbol->l_exp->const_value_real) - *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(mul_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		if ((*(symbol->l_exp->const_value_integer) == 0) ||
+			(*(symbol->r_exp->const_value_integer) == 0)) {
+			*(symbol->const_value_integer) = 0;
+			return NULL;
+		}
+
+		*(symbol->const_value_integer) = *(symbol->l_exp->const_value_integer) * *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		symbol->const_value_real = (double*) malloc(sizeof(double));
+		*(symbol->const_value_real) = *(symbol->l_exp->const_value_real) * *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(div_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		if (*(symbol->r_exp->const_value_integer) == 0)
+			STAGE3_ERROR(0, symbol, symbol, "Division by zero in constant expression.");
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_integer) = *(symbol->l_exp->const_value_integer) / *(symbol->r_exp->const_value_integer);
+	}
+	if (DO_OPER(real)) {
+		if (*(symbol->r_exp->const_value_real) == 0)
+			STAGE3_ERROR(0, symbol, symbol, "Division by zero in constant expression.");
+		symbol->const_value_real = (double*) malloc(sizeof(double));
+		*(symbol->const_value_real) = *(symbol->l_exp->const_value_real) / *(symbol->r_exp->const_value_real);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(mod_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if (DO_OPER(integer)) {
+		if (*(symbol->r_exp->const_value_integer) == 0)
+			STAGE3_ERROR(0, symbol, symbol, "Division by zero in constant expression.");
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_integer) = *(symbol->l_exp->const_value_integer) % *(symbol->r_exp->const_value_integer);
+	}
+
+	return NULL;
+}
+
+void *constant_folding_c::visit(power_expression_c *symbol) {
+	symbol->l_exp->accept(*this);
+	symbol->r_exp->accept(*this);
+	if ((NULL != symbol->l_exp->const_value_real) && (NULL != symbol->r_exp->const_value_integer)) {
+		symbol->const_value_real = (double*) malloc(sizeof(double));
+		*(symbol->const_value_real) = pow(*(symbol->l_exp->const_value_real), *(symbol->r_exp->const_value_integer));
+	}
+
+	return NULL;
+}
+void *constant_folding_c::visit(neg_expression_c *symbol) {
+	symbol->exp->accept(*this);
+	if (NULL != symbol->exp->const_value_integer) {
+		symbol->const_value_integer = (int64_t*) malloc(sizeof(int64_t));
+		*(symbol->const_value_integer) = - *(symbol->exp->const_value_integer);
+	}
+	if (NULL != symbol->exp->const_value_real) {
+		symbol->const_value_real = (double*) malloc(sizeof(double));
+		*(symbol->const_value_real) = - *(symbol->exp->const_value_real);
+	}
+	return NULL;
+}
+
+void *constant_folding_c::visit(not_expression_c *symbol) {
+	symbol->exp->accept(*this);
+	if (NULL != symbol->exp->const_value_bool) {
+		symbol->const_value_bool = (bool*) malloc(sizeof(bool));
+		*(symbol->const_value_bool) = !*(symbol->exp->const_value_bool);
+	}
+
+	return NULL;
+}
+
+
+
diff -r 61410284a9b4 -r dabffc3086dc stage3/constant_folding.hh
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/stage3/constant_folding.hh	Tue Jun 05 19:17:29 2012 +0200
@@ -0,0 +1,103 @@
+/*
+ *  matiec - a compiler for the programming languages defined in IEC 61131-3
+ *
+ *  Copyright (C) 2009-2012  Mario de Sousa (msousa@fe.up.pt)
+ *  Copyright (C) 2012       Manuele Conti (conti.ma@alice.it)
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ * This code is made available on the understanding that it will not be
+ * used in safety-critical situations without a full and competent review.
+ */
+
+/*
+ * An IEC 61131-3 compiler.
+ *
+ * Based on the
+ * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
+ *
+ */
+
+/* Determine the data type of an constant expression.
+ * A reference to the relevant type definition is returned.
+ *
+ * For example:
+ *       2 + 3       -> returns reference 
+ *       22.2 - 5    -> returns reference
+ *       etc...
+ */
+
+#include <vector>
+#include "../absyntax_utils/absyntax_utils.hh"
+
+
+
+class constant_folding_c : public iterator_visitor_c {
+    search_varfb_instance_type_c *search_varfb_instance_type;
+    search_base_type_c search_base_type;
+    int error_count;
+    int current_display_error_level;
+
+public:
+	constant_folding_c(symbol_c *symbol = NULL);
+	virtual ~constant_folding_c(void);
+	int get_error_count();
+
+private:
+    /*********************/
+    /* B 1.2 - Constants */
+    /*********************/
+    /******************************/
+    /* B 1.2.1 - Numeric Literals */
+    /******************************/
+    void *visit(real_c *symbol);
+    void *visit(integer_c *symbol);
+    void *visit(neg_real_c *symbol);
+    void *visit(neg_integer_c *symbol);
+    void *visit(binary_integer_c *symbol);
+    void *visit(octal_integer_c *symbol);
+    void *visit(hex_integer_c *symbol);
+    void *visit(integer_literal_c *symbol);
+    void *visit(real_literal_c *symbol);
+    void *visit(bit_string_literal_c *symbol);
+    void *visit(boolean_literal_c *symbol);
+    void *visit(boolean_true_c *symbol);
+    void *visit(boolean_false_c *symbol);
+
+    /***************************************/
+    /* B.3 - Language ST (Structured Text) */
+    /***************************************/
+    /***********************/
+    /* B 3.1 - Expressions */
+    /***********************/
+    void *visit(or_expression_c *symbol);
+    void *visit(xor_expression_c *symbol);
+    void *visit(and_expression_c *symbol);
+    void *visit(equ_expression_c *symbol);
+    void *visit(notequ_expression_c *symbol);
+    void *visit(lt_expression_c *symbol);
+    void *visit(gt_expression_c *symbol);
+    void *visit(le_expression_c *symbol);
+    void *visit(ge_expression_c *symbol);
+    void *visit(add_expression_c *symbol);
+    void *visit(sub_expression_c *symbol);
+    void *visit(mul_expression_c *symbol);
+    void *visit(div_expression_c *symbol);
+    void *visit(mod_expression_c *symbol);
+    void *visit(power_expression_c *symbol);
+    void *visit(neg_expression_c *symbol);
+    void *visit(not_expression_c *symbol);
+};
+
diff -r 61410284a9b4 -r dabffc3086dc stage3/stage3.cc
--- a/stage3/stage3.cc	Tue Jun 05 11:10:12 2012 +0200
+++ b/stage3/stage3.cc	Tue Jun 05 19:17:29 2012 +0200
@@ -40,12 +40,18 @@
 #include "print_datatypes_error.hh"
 #include "lvalue_check.hh"
 #include "array_range_check.hh"
+#include "constant_folding.hh"
 
+static int constant_check(symbol_c *tree_root){
+    constant_folding_c constant_folding(tree_root);
+    tree_root->accept(constant_folding);
+    return constant_folding.get_error_count();
+}
 
 static int flow_control_analysis(symbol_c *tree_root){
-  flow_control_analysis_c flow_control_analysis(tree_root);
-  tree_root->accept(flow_control_analysis);
-  return 0;
+    flow_control_analysis_c flow_control_analysis(tree_root);
+    tree_root->accept(flow_control_analysis);
+    return 0;
 }
 
 
@@ -81,6 +87,7 @@
 
 int stage3(symbol_c *tree_root){
 	int error_count = 0;
+	error_count += constant_check(tree_root);
 	error_count += flow_control_analysis(tree_root);
 	error_count += type_safety(tree_root);
 	error_count += lvalue_check(tree_root);