diff --git a/vhdlpp/Makefile.in b/vhdlpp/Makefile.in
index 7717473fb..4e51a4d1b 100644
--- a/vhdlpp/Makefile.in
+++ b/vhdlpp/Makefile.in
@@ -57,10 +57,10 @@ CXXFLAGS = @WARNING_FLAGS@ @WARNING_FLAGS_CXX@ @CXXFLAGS@
 LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@ @EXTRALIBS@
 
-M = StringHeap.o LineInfo.o
+M = StringHeap.o LineInfo.o 
 
 O = main.o compiler.o entity.o entity_elaborate.o \
-    lexor.o lexor_keyword.o parse.o $M
+    lexor.o lexor_keyword.o parse.o vhdlreal.o vhdlint.o $M
 
 all: dep vhdlpp@EXEEXT@
 
diff --git a/vhdlpp/lexor.lex b/vhdlpp/lexor.lex
index dd59ad95b..f00addcb9 100644
--- a/vhdlpp/lexor.lex
+++ b/vhdlpp/lexor.lex
@@ -19,17 +19,20 @@
  *    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, write to the Free Software
+ *    aint64_t with this program; if not, write to the Free Software
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 
 # include  "parse_api.h"
 # include  "lexor_keyword.h"
-# include  "vhdlnum.h"
+# include  "vhdlint.h"
 # include  "vhdlreal.h"
 # include  "parse_wrap.h"
 
+# include  <cmath>
+# include  <cassert>
 # include  <iostream>
+# include  <set>
 
 //class vhdlnum;
 //class vhdlreal;
@@ -45,10 +48,16 @@ extern int lexor_keyword_code (const char*str, unsigned len);
  */
 extern YYLTYPE yylloc;
 
-static int check_underscores(char* text);
+static bool are_underscores_correct(char* text);
+static bool is_based_correct(char* text);
+static char* escape_quot_and_dup(char* text);
+static char* escape_apostrophe_and_dup(char* text);
 
-vhdlnum* make_unisized_dec(char* text);
-vhdlnum* make_unisized_based(char* text);
+static double make_double_from_based(char* text);
+static int64_t make_long_from_based(char* text);
+
+static int64_t lpow(int64_t left, int64_t right);
+static unsigned short short_from_hex_char(char ch);
 
 static char* strdupnew(char const *str)
 {
@@ -90,13 +99,26 @@ based_integer		[0-9a-fA-F](_?[0-9a-fA-F])*
 <CCOMMENT>\n   { yylloc.first_line += 1; }
 <CCOMMENT>"*/" { BEGIN(comment_enter); }
 
+\'.\' { 
+    yylval.text = escape_apostrophe_and_dup(yytext);
+    return CHARACTER_LITERAL;
+}
+
+(\"([^"]|(\"\"))*?\")|(\"[^\"]*\")  {
+/* first pattern: string literals with doubled quotation mark */
+/* second pattern: string literals without doubled quotation */
+    yylval.text = escape_quot_and_dup(yytext);
+    assert(yylval.text);
+    return STRING_LITERAL;
+}
 
 [a-zA-Z][a-zA-Z0-9_]* {
       int rc = lexor_keyword_code(yytext, yyleng);
       switch (rc) {
 	  case IDENTIFIER:
-		if(check_underscores(yytext))
-			std::cerr << "An invalid underscore in the identifier" << std::endl;
+		if(!are_underscores_correct(yytext))
+			std::cerr << "An invalid underscore in the identifier:"
+                    << yytext << std::endl;
                 //yywarn(yylloc, "An invalid underscore in the identifier"); 
 	    yylval.text = strdupnew(yytext);
 	    break;
@@ -106,26 +128,43 @@ based_integer		[0-9a-fA-F](_?[0-9a-fA-F])*
       return rc;
   }
   
-\\(.|\\\\)*\\ { /* extended identifiers */
+\\([^\\]|\\\\)*\\ { /* extended identifiers */
     yylval.text = strdupnew(yytext);
-    printf("special %s\n", yytext);  
     return IDENTIFIER;    
 }
 
    
 {decimal_literal} {
+    if(!are_underscores_correct(yytext))
+        std::cerr << "An invalid underscore in the decimal literal:" 
+            << yytext << std::endl;
+    
     if(strchr(yytext, '.')) {
         yylval.real = new vhdlreal(yytext);
         return REAL_LITERAL;
     } else {
-        yylval.integer = new vhdlnum(yytext); 
+        yylval.integer = new vhdlint(yytext); 
         return INT_LITERAL;
     }
 }
 
 {based_literal} {
-    yylval.integer = new vhdlnum(yytext); 
-    return INT_LITERAL;
+    if(!are_underscores_correct(yytext) || !is_based_correct(yytext))
+        std::cerr << "An invalid form of based literal:" 
+            << yytext << std::endl;
+            
+    if(strchr(yytext, '.'))
+    {
+        double val = make_double_from_based(yytext);
+        yylval.real = new vhdlreal(val);
+        return REAL_LITERAL;
+    }
+    else
+    {
+        int64_t val = make_long_from_based(yytext);
+        yylval.integer = new vhdlint(val);
+        return INT_LITERAL;
+    }
 }
 
     
@@ -158,7 +197,14 @@ based_integer		[0-9a-fA-F](_?[0-9a-fA-F])*
 
 extern void yyparse_set_filepath(const char*path);
 
-static int check_underscores(char* text) 
+/**
+* This function checks if underscores in an identifier
+* or in a number are correct.
+*
+* \return true is returned if underscores are placed
+* correctly according to specification
+*/
+static bool are_underscores_correct(char* text) 
 {
 	unsigned char underscore_allowed = 0;
 	const char* cp;
@@ -167,13 +213,285 @@ static int check_underscores(char* text)
 		if (*cp == '_')
 		{
 			if (!underscore_allowed || *(cp+1) == '\0')
-				return 1;
+				return 0;
 			underscore_allowed = 0;
 		}
 		else
 			underscore_allowed = 1;
 	}
-	return 0;
+	return 1;
+}
+
+/**
+* This function checks if the format of a based number
+* is correct according to the VHDL standard
+*
+* \return true is returned if a based number
+* is formed well according to specification
+*/
+static bool is_based_correct(char* text)
+{
+    char* ptr;
+    //BASE examination
+    char clean_base[4];
+    clean_base[3] = '\0';
+    char* clean_base_ptr = clean_base;
+    for(ptr = text; ptr != strchr(text, '#'); ++ptr)
+    {
+        if(*ptr == '_')
+            ++ptr;
+        if(!(*ptr >= '0' && *ptr <= '9')) //the base uses chars other than digits
+            return 0;
+        if(*clean_base_ptr == '\0')
+            break;
+        *clean_base_ptr = *ptr;
+        ++clean_base_ptr;
+    }
+    unsigned length = clean_base_ptr - clean_base;
+    unsigned base; 
+    if(length > 2 || length == 0)
+        return 0; //the base is too big or too small
+    if(length == 2)
+    {
+        base = 10*(clean_base[0] - '0') + (clean_base[1] - '0'); 
+        //the base exceeds 16 or equals 0
+        if(base > 16 || base == 0)
+            return 0;
+    }
+    else
+    { //the base consists of one char and is equal to zero
+        base = clean_base[0] - '0';
+        if(base == 0)
+            return 0;
+    }
+    bool point = 0;
+    set<char> allowed_chars;
+    
+    unsigned c;
+    if(base <= 10) {
+        for(c = 0; c < base; ++c)
+            allowed_chars.insert(c + '0');
+    }
+    else
+    {
+        for(c = 0; c < 10; ++c)
+            allowed_chars.insert(c + '0');
+        for(c = 0; c < base - 10; ++c)
+            allowed_chars.insert(c + 'a');
+    }
+    //MANTISSA examination
+    for(ptr = strchr(text, '#') + 1, length = 0; ptr != strrchr(text, '#'); ++ptr)
+    {
+        if(*ptr == '.') 
+        {
+            //we found a dot and another one was already found
+            if(point == 1)
+                return 0;
+            else
+            {
+                //notice the fact of finding a point and continue, without increasing the length
+                point = 1;
+                continue;
+            }
+        }
+        //the number consists of other chars than allowed
+        if(allowed_chars.find(*ptr) == allowed_chars.end())
+            return 0;
+        ++length;
+    }
+    if(length == 0)
+        return 0;
+    
+    //EXPONENT examination
+    if(strchr(text, '\0') - strrchr(text, '#') > 1) { //the number contains an exponent
+        if(*(strrchr(text, '#') + 2) == '-')
+            return 0;
+        length = 0;
+        for(ptr = strrchr(text, '#')+2; *ptr != '\0'; ++ptr)
+        {
+            //the exponent consists of other chars than {'0'.,'9','a'..'f'}
+            if(!((*ptr >= '0' && *ptr <= '9') || (*ptr >= 'a' && *ptr <= 'f')))
+                return 0;
+        }
+    } 
+    return 1;
+}
+
+/**
+* This function takes a string literal, gets rid of
+* quotation marks and copies the remaining characters
+* to a new persistent C-string
+*
+* \return pointer to the new string is returned
+*/
+static char* escape_quot_and_dup(char* text)
+{
+    char* newstr = new char[strlen(text)+1];
+    
+    unsigned old_idx, new_idx;
+    for(new_idx = 0, old_idx = 0; old_idx < strlen(text); ) 
+    {
+        if(text[old_idx] == '"' && old_idx == 0) 
+        { //the beginning of the literal
+            ++old_idx; 
+            continue;
+        }
+        else
+        if(text[old_idx] == '"' && text[old_idx+1] == '\0')
+        { //the end
+            newstr[new_idx] = '\0';
+            return newstr;
+        }
+        else
+        if(text[old_idx] == '"' && text[old_idx+1] == '"') 
+        {
+            newstr[new_idx++] = '"';
+            old_idx += 2; //jump across two chars
+        }
+        else 
+        {
+            newstr[new_idx] = text[old_idx];
+            ++old_idx;
+            ++new_idx;
+        }
+    }
+    //the function should never reach this point
+    return 0;
+}
+
+/**
+* This function takes a character literal, gets rid
+* of the apostrophes and returns new C-string
+*
+* \return pointer to the new string is returned
+*/
+static char* escape_apostrophe_and_dup(char* text)
+{
+    char* newstr = new char[2];
+    newstr[0] = text[1];
+    newstr[1] = '\0';
+    return newstr;
+}
+
+/**
+* This function takes a floating point based number 
+* in form of a C-strings and converts it to a double.
+*
+* \return new double is returned
+*/
+static double make_double_from_based(char* text)
+{
+    char* first_hash_ptr = strchr(text, '#');
+    char* second_hash_ptr = strrchr(text, '#');
+    char* last_char_ptr = strchr(text, '\0') - 1;
+    //put null byte in lieu of hashes
+    *first_hash_ptr = '\0';
+    *second_hash_ptr = '\0';
+    
+    //now lets deduce the base
+    unsigned base = (unsigned)strtol(text, 0, 10) ;
+    
+    double mantissa = 0.0;
+    char*ptr = first_hash_ptr + 1;
+    for( ; ptr != second_hash_ptr ; ++ptr)
+    {
+        if(*ptr == '.')
+            break;
+        if(*ptr != '_')
+        {
+            mantissa = mantissa*base + short_from_hex_char(*ptr);
+        }
+    }
+    double fraction = 0.0;
+    double factor = 1.0/base;
+    for(++ptr ; ptr != second_hash_ptr; ++ptr)
+    {
+        if(*ptr != '_')
+        {
+            fraction = fraction + short_from_hex_char(*ptr)*factor;
+            factor = factor / base;
+        }
+    }
+    if(last_char_ptr == second_hash_ptr) //there is no exponent
+    {
+        return mantissa + fraction;
+    }
+    
+    //now calculate the value of the exponent
+    double exponent = 0.0;
+    //leave 'e'/'E' and '+'
+    ptr = *(second_hash_ptr + 2) == '+' ? second_hash_ptr + 3 : second_hash_ptr + 2;  
+    
+    for( ; *ptr != '\0'; ++ptr)
+    {
+        if(*ptr != '_')
+        {
+            exponent = exponent*base + short_from_hex_char(*ptr);
+        }
+    }
+    return pow(mantissa + fraction, exponent);
+}   
+
+/** 
+* This function takes a hexadecimal digit in form of
+* a char and returns its litteral value as short
+*/
+static unsigned short short_from_hex_char(char ch) 
+{
+    if(ch >= '0' && ch <= '9')
+        return ch - '0';
+    else
+        return ch - 'a' + 10;
+}
+
+/**
+* This function takes a based number in form of
+* a C-strings and converts it to a int64_t.
+*
+* \return new double is returned
+*/
+static int64_t make_long_from_based(char* text) {
+    char* first_hash_ptr = strchr(text, '#');
+    char* second_hash_ptr = strrchr(text, '#');
+    char* end_ptr = strrchr(text, '\0');
+    //now lets deduce the base
+    *first_hash_ptr = '\0'; 
+    unsigned base = (unsigned)strtol(text, 0, 10) ;
+    
+    char *ptr = first_hash_ptr + 1;
+    int64_t mantissa = 0;
+    for( ; ptr != second_hash_ptr ; ++ptr)
+    {
+        if(*ptr != '_')
+        {
+            mantissa = mantissa * base + short_from_hex_char(*ptr);
+        }
+    }
+    //if there is an exponent
+    if(end_ptr - second_hash_ptr > 1)
+    {
+       int64_t exponent = 0L; 
+       
+       ptr = *(second_hash_ptr + 2) == '+' ? second_hash_ptr + 3 : second_hash_ptr + 2; 
+       for( ; *ptr != '\0'; ++ptr)
+       {
+           if(*ptr != '_')
+               exponent = base*exponent + short_from_hex_char(*ptr);
+       }
+       return lpow(mantissa, exponent);
+    }
+    else
+        return mantissa;
+}
+
+/**
+* Recursive power function for int64_t
+*/
+static int64_t lpow(int64_t left, int64_t right) {
+    if(right == 0)
+        return 1;
+    else
+        return left*lpow(left, right - 1);
 }
 
 void reset_lexor(FILE*fd, const char*path)
diff --git a/vhdlpp/parse.y b/vhdlpp/parse.y
index 9c24a65a1..d5f8de0e9 100644
--- a/vhdlpp/parse.y
+++ b/vhdlpp/parse.y
@@ -20,7 +20,7 @@
  */
 
 # include "vhdlpp_config.h"
-# include "vhdlnum.h"
+# include "vhdlint.h"
 # include "vhdlreal.h"
 # include "compiler.h"
 # include "parse_api.h"
@@ -45,7 +45,7 @@ int parse_errors = 0;
 %union {
       port_mode_t port_mode;
       char*text;
-      vhdlnum* integer;
+      vhdlint* integer;
       vhdlreal* real;
       
       InterfacePort*interface_element;
diff --git a/vhdlpp/parse_wrap.h b/vhdlpp/parse_wrap.h
index 2d09ecd62..c5a30e353 100644
--- a/vhdlpp/parse_wrap.h
+++ b/vhdlpp/parse_wrap.h
@@ -26,7 +26,7 @@
  */
 
 # include  <list>
-# include "vhdlnum.h"
+# include "vhdlint.h"
 # include "vhdlreal.h"
 # include  "parse.h"
 
diff --git a/vhdlpp/vhdlint.cc b/vhdlpp/vhdlint.cc
new file mode 100644
index 000000000..e2486b040
--- /dev/null
+++ b/vhdlpp/vhdlint.cc
@@ -0,0 +1,68 @@
+#include "config.h"
+#include "vhdlint.h"
+#include <cstring>
+#include <cstdlib>
+#include <sstream>
+
+bool vhdlint::is_negative() const
+{
+    return value_ < 0L;
+}
+
+bool vhdlint::is_positive() const
+{
+    return value_ > 0L;
+}
+
+bool vhdlint::is_zero() const
+{
+    return value_ == 0L;
+}
+
+vhdlint::vhdlint(const char* text)
+{
+    unsigned text_length = strlen(text);
+    if(text_length == 0)
+    {
+        value_ = 0L;
+        return;
+    }
+    
+    char* new_text = new char[text_length + 1];
+    
+    const char* ptr;
+    char* new_ptr;
+    for(ptr = text, new_ptr = new_text; *ptr != '\0'; ++ptr)
+    {
+        if(*ptr == '_')
+            continue;
+        else
+        {
+            *new_ptr = *ptr;
+            ++new_ptr;
+            ++ptr;
+        }
+    }
+    *new_ptr = '\0';
+    
+    istringstream str(new_text);
+    delete[] new_text;
+    
+    //TODO: check if numbers greater than MAX_INT are handled correctly
+    str >> value_;
+}
+
+vhdlint::vhdlint(const int64_t& val)
+{
+    value_ = val;
+}
+
+vhdlint::vhdlint(const vhdlint& val)
+{
+    value_ = val.as_long();
+}
+
+int64_t vhdlint::as_long() const
+{
+    return value_;
+}
\ No newline at end of file
diff --git a/vhdlpp/vhdlint.h b/vhdlpp/vhdlint.h
new file mode 100644
index 000000000..0ef5ef54a
--- /dev/null
+++ b/vhdlpp/vhdlint.h
@@ -0,0 +1,28 @@
+#ifndef __vhdlint_H
+#define __vhdlint_H
+
+#include "config.h"
+#include <stdint.h>
+
+using namespace std;
+
+class vhdlint
+{
+    public:
+        explicit vhdlint(const char* text);
+        explicit vhdlint(const int64_t& val);
+        explicit vhdlint(const vhdlint& val);
+        
+        bool is_negative() const;
+        bool is_positive() const;
+        bool is_zero() const;
+        
+        int64_t as_long() const;
+        //vhdlv get(const unsigned index) const;
+        //void set(const unsigned index, const unsigned val);
+       // unsigned short operator[](const unsigned index);
+    private:
+        int64_t value_;
+};
+
+#endif
diff --git a/vhdlpp/vhdlreal.cc b/vhdlpp/vhdlreal.cc
new file mode 100644
index 000000000..fd903d544
--- /dev/null
+++ b/vhdlpp/vhdlreal.cc
@@ -0,0 +1,59 @@
+#include "config.h"
+#include "compiler.h"
+#include "vhdlreal.h"
+#include <assert.h>
+#include <cstring>
+#include <cstdlib>
+
+vhdlreal::vhdlreal() {
+    value_ = 0.0;
+}
+
+vhdlreal::vhdlreal(const double& r) {
+    value_ = r;
+}
+
+vhdlreal::vhdlreal(const vhdlreal& val) {
+    value_ = val.as_double();
+}
+
+vhdlreal::vhdlreal(const char* text) {
+    assert(strlen(text) != 0);
+    char* buffer = new char[strlen(text)+1];
+    
+    char* buf_ptr;
+    for(buf_ptr = buffer; *text != 0; ++buf_ptr, ++text) {
+        if(*text == '_')
+            continue;
+        *buf_ptr = *text;
+    }
+    *buf_ptr = '\0';
+    
+    value_ = strtod(buffer, NULL);
+    delete[] buffer;
+}
+
+ostream& operator<< (ostream& str, const vhdlreal& r) {
+    return (str << r.as_double());
+}
+vhdlreal operator+ (const vhdlreal& r1, const vhdlreal& r2) {
+    return vhdlreal(r1.as_double() + r2.as_double());
+}
+vhdlreal operator- (const vhdlreal& r1, const vhdlreal& r2) {
+    return vhdlreal(r1.as_double() - r2.as_double());
+}
+vhdlreal operator* (const vhdlreal& r1, const vhdlreal& r2) {
+    return vhdlreal(r1.as_double() * r2.as_double());
+}
+vhdlreal operator/ (const vhdlreal& r1, const vhdlreal& r2) {
+    return vhdlreal(r1.as_double() / r2.as_double());
+}
+vhdlreal operator% (const vhdlreal& r1, const vhdlreal& r2) {
+    return vhdlreal(fmod(r1.as_double(), r2.as_double()));
+}
+vhdlreal pow(const vhdlreal& r1, const vhdlreal& r2) {
+    return vhdlreal(pow(r1.as_double(), r2.as_double()));
+}
+vhdlreal operator- (const vhdlreal& r) {
+    return vhdlreal(-r.as_double());
+}
\ No newline at end of file
diff --git a/vhdlpp/vhdlreal.h b/vhdlpp/vhdlreal.h
index c74263fdd..72c41f101 100644
--- a/vhdlpp/vhdlreal.h
+++ b/vhdlpp/vhdlreal.h
@@ -2,10 +2,39 @@
 #define __vhdlreal_h
 
 #include "config.h"
+#include <iostream>
+#include <cmath>
 
-class vhdlreal {
-    public:
-        vhdlreal(char* text) {}
+using namespace std;
+/*
+* This class holds a floating point decimal number. The number is
+* stored as double. All based numbers are converted by an external
+* function to a double and then stored as class instance.
+*/
+class vhdlreal
+{
+public: 
+    friend ostream& operator<< (ostream&, const vhdlreal&);
+    friend vhdlreal operator+ (const vhdlreal&, const vhdlreal&);
+    friend vhdlreal operator- (const vhdlreal&, const vhdlreal&);
+    friend vhdlreal operator* (const vhdlreal&, const vhdlreal&);
+    friend vhdlreal operator/ (const vhdlreal&, const vhdlreal&);
+    friend vhdlreal operator% (const vhdlreal&, const vhdlreal&);
+    friend vhdlreal pow(const vhdlreal&, const vhdlreal&);
+    // Unary minus.
+    friend vhdlreal operator- (const vhdlreal&);
+
+    explicit vhdlreal();
+    explicit vhdlreal(const char*text);
+    explicit vhdlreal(const double& val);
+    vhdlreal(const vhdlreal& val);
+    virtual ~vhdlreal() {};
+    
+    double as_double() const
+    {
+        return value_;
+    }
+protected:
+    double value_;
 };
-
-#endif
+#endif
\ No newline at end of file