1

/*

     2

 *  matiec - a compiler for the programming languages defined in IEC 61131-3

     3

 *

     4

 *  Copyright (C) 2009-2011  Mario de Sousa (msousa@fe.up.pt)

     5

 *  Copyright (C) 2007-2011  Laurent Bessard and Edouard Tisserant

     6

 *

     7

 *  This program is free software: you can redistribute it and/or modify

     8

 *  it under the terms of the GNU General Public License as published by

     9

 *  the Free Software Foundation, either version 3 of the License, or

    10

 *  (at your option) any later version.

    11

 *

    12

 *  This program is distributed in the hope that it will be useful,

    13

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

    14

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    15

 *  GNU General Public License for more details.

    16

 *

    17

 *  You should have received a copy of the GNU General Public License

    18

 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.

    19

 *

    20

 *

    21

 * This code is made available on the understanding that it will not be

    22

 * used in safety-critical situations without a full and competent review.

    23

 */

    24

    25

/*

    26

 * An IEC 61131-3 compiler.

    27

 *

    28

 * Based on the

    29

 * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)

    30

 *

    31

 */

    32

    33

    34

/* Verify whether the semantic rules of data type compatibility are being followed.

    35

 *

    36

 * For example:

    37

 */

    38

    39

#include "visit_expression_type.hh"

    40

#include <typeinfo>

    41

#include <list>

    42

#include <string>

    43

#include <string.h>

    44

#include <strings.h>

    45

    46

    47

#define FIRST_(symbol1, symbol2) (((symbol1)->first_order < (symbol2)->first_order)   ? (symbol1) : (symbol2))

    48

#define  LAST_(symbol1, symbol2) (((symbol1)->last_order  > (symbol2)->last_order)    ? (symbol1) : (symbol2))

    49

    50

#define STAGE3_ERROR(symbol1, symbol2, ...) {                                          \

    51

    fprintf(stderr, "%s:%d-%d..%d-%d: error : ",                                       \

    52

           FIRST_(symbol1,symbol2)->first_file, FIRST_(symbol1,symbol2)->first_line, FIRST_(symbol1,symbol2)->first_column, \

    53

                                                LAST_(symbol1,symbol2) ->last_line,  LAST_(symbol1,symbol2) ->last_column); \

    54

    fprintf(stderr, __VA_ARGS__);                                                      \

    55

    fprintf(stderr, "\n");                                                             \

    56

    il_error = true;                                                                   \

    57

    error_found = true;                                                                \

    58

  }

    59

    60

    61

/* set to 1 to see debug info during execution */

    62

static int debug = 0;

    63

    64

    65

void *visit_expression_type_c::visit(program_declaration_c *symbol) {

    66

  search_varfb_instance_type = new search_varfb_instance_type_c(symbol);

    67

  symbol->var_declarations->accept(*this);

    68

  if (debug) printf("checking semantics in body of program %s\n", ((token_c *)(symbol->program_type_name))->value);

    69

  il_parenthesis_level = 0;

    70

  il_error = false;

    71

  il_default_variable_type = NULL;

    72

  symbol->function_block_body->accept(*this);

    73

  il_default_variable_type = NULL;

    74

  delete search_varfb_instance_type;

    75

  search_varfb_instance_type = NULL;

    76

  return NULL;

    77

}

    78

    79

void *visit_expression_type_c::visit(function_declaration_c *symbol) {

    80

  search_varfb_instance_type = new search_varfb_instance_type_c(symbol);

    81

  symbol->var_declarations_list->accept(*this);

    82

  if (debug) printf("checking semantics in body of function %s\n", ((token_c *)(symbol->derived_function_name))->value);

    83

  il_parenthesis_level = 0;

    84

  il_error = false;

    85

  il_default_variable_type = NULL;

    86

  symbol->function_body->accept(*this);

    87

  il_default_variable_type = NULL;

    88

  delete search_varfb_instance_type;

    89

  search_varfb_instance_type = NULL;

    90

  return NULL;

    91

}

    92

    93

void *visit_expression_type_c::visit(function_block_declaration_c *symbol) {

    94

  search_varfb_instance_type = new search_varfb_instance_type_c(symbol);

    95

  symbol->var_declarations->accept(*this);

    96

  if (debug) printf("checking semantics in body of FB %s\n", ((token_c *)(symbol->fblock_name))->value);

    97

  il_parenthesis_level = 0;

    98

  il_error = false;

    99

  il_default_variable_type = NULL;

   100

  symbol->fblock_body->accept(*this);

   101

  il_default_variable_type = NULL;

   102

  delete search_varfb_instance_type;

   103

  search_varfb_instance_type = NULL;

   104

  return NULL;

   105

}

   106

   107

   108

   109

   110

   111

   112

   113

   114

   115

visit_expression_type_c::visit_expression_type_c(symbol_c *ignore) {

   116

  error_found = false;

   117

}

   118

   119

visit_expression_type_c::~visit_expression_type_c(void) {

   120

}

   121

   122

bool visit_expression_type_c::get_error_found(void) {

   123

  return error_found;

   124

}

   125

   126

   127

   128

/* NOTE on data type handling and literals...

   129

 * ==========================================

   130

 *

   131

 * Literals that are explicitly type cast 

   132

 *   e.g.:   BYTE#42

   133

 *           INT#65

   134

 *           TIME#45h23m

   135

 *               etc...

   136

 *  are NOT considered literals in the following code.

   137

 *  Since they are type cast, and their data type is fixed and well known,

   138

 *  they are treated as a variable of that data type (except when determining lvalues)

   139

 *  In other words, when calling search_constant_type_c on these constants, it returns

   140

 *  a xxxxx_type_name_c, and not one of the xxxx_literal_c ! 

   141

 *

   142

 *  When the following code handles a literal, it is really a literal of unknown data type.

   143

 *    e.g.   42, may be considered an int, a byte, a word, etc... 

   144

 *

   145

 * NOTE: type_symbol == NULL is valid!

   146

 *       This will occur, for example, when and undefined/undeclared symbolic_variable is used in the program.

   147

 *       This will not be of any type, so we always return false.

   148

 */

   149

   150

/* A helper function... */

   151

bool visit_expression_type_c::is_ANY_ELEMENTARY_type(symbol_c *type_symbol) {

   152

  if (type_symbol == NULL) {return false;}

   153

  return is_ANY_MAGNITUDE_type(type_symbol)

   154

      || is_ANY_BIT_type      (type_symbol)

   155

      || is_ANY_STRING_type   (type_symbol)

   156

      || is_ANY_DATE_type     (type_symbol);

   157

}

   158

   159

/* A helper function... */

   160

bool visit_expression_type_c::is_ANY_SAFEELEMENTARY_type(symbol_c *type_symbol) {

   161

  if (type_symbol == NULL) {return false;}

   162

  return is_ANY_SAFEMAGNITUDE_type(type_symbol)

   163

      || is_ANY_SAFEBIT_type      (type_symbol)

   164

      || is_ANY_SAFESTRING_type   (type_symbol)

   165

      || is_ANY_SAFEDATE_type     (type_symbol);

   166

}

   167

   168

/* A helper function... */

   169

bool visit_expression_type_c::is_ANY_ELEMENTARY_compatible(symbol_c *type_symbol) {

   170

  if (type_symbol == NULL) {return false;}

   171

  /* NOTE: doing 

   172

   *          return is_ANY_SAFEELEMENTARY_type() || is_ANY_ELEMENTARY_type()

   173

   *       is incorrect, as the literals would never be considered compatible...

   174

   */

   175

  return is_ANY_MAGNITUDE_compatible(type_symbol)

   176

      || is_ANY_BIT_compatible      (type_symbol)

   177

      || is_ANY_STRING_compatible   (type_symbol)

   178

      || is_ANY_DATE_compatible     (type_symbol);

   179

}

   180

   181

   182

/* A helper function... */

   183

bool visit_expression_type_c::is_ANY_MAGNITUDE_type(symbol_c *type_symbol) {

   184

  if (type_symbol == NULL) {return false;}

   185

  if (typeid(*type_symbol) == typeid(time_type_name_c)) {return true;}

   186

  return is_ANY_NUM_type(type_symbol);

   187

}

   188

   189

/* A helper function... */

   190

bool visit_expression_type_c::is_ANY_SAFEMAGNITUDE_type(symbol_c *type_symbol) {

   191

  if (type_symbol == NULL) {return false;}

   192

  if (typeid(*type_symbol) == typeid(safetime_type_name_c)) {return true;}

   193

  return is_ANY_SAFENUM_type(type_symbol);

   194

}

   195

   196

/* A helper function... */

   197

bool visit_expression_type_c::is_ANY_MAGNITUDE_compatible(symbol_c *type_symbol) {

   198

  if (type_symbol == NULL) {return false;}

   199

  if (is_ANY_MAGNITUDE_type    (type_symbol))              {return true;}

   200

  if (is_ANY_SAFEMAGNITUDE_type(type_symbol))              {return true;}

   201

   202

  return is_ANY_NUM_compatible(type_symbol);

   203

}

   204

   205

/* A helper function... */

   206

bool visit_expression_type_c::is_ANY_NUM_type(symbol_c *type_symbol) {

   207

  if (type_symbol == NULL) {return false;}

   208

  if (is_ANY_REAL_type(type_symbol))                       {return true;}

   209

  if (is_ANY_INT_type(type_symbol))                        {return true;}

   210

  return false;

   211

}

   212

   213

/* A helper function... */

   214

bool visit_expression_type_c::is_ANY_SAFENUM_type(symbol_c *type_symbol) {

   215

  if (type_symbol == NULL) {return false;}

   216

  return is_ANY_SAFEREAL_type(type_symbol) 

   217

      || is_ANY_SAFEINT_type (type_symbol);

   218

}

   219

   220

/* A helper function... */

   221

bool visit_expression_type_c::is_ANY_NUM_compatible(symbol_c *type_symbol) {

   222

  if (type_symbol == NULL) {return false;}

   223

  if (is_ANY_REAL_compatible(type_symbol))                       {return true;}

   224

  if (is_ANY_INT_compatible(type_symbol))                        {return true;}

   225

  return false;  

   226

}

   227

   228

/* A helper function... */

   229

bool visit_expression_type_c::is_ANY_DATE_type(symbol_c *type_symbol) {

   230

  if (type_symbol == NULL) {return false;}

   231

  if (typeid(*type_symbol) == typeid(date_type_name_c)) {return true;}

   232

  if (typeid(*type_symbol) == typeid(tod_type_name_c))  {return true;}

   233

  if (typeid(*type_symbol) == typeid(dt_type_name_c))   {return true;}

   234

  return false;

   235

}

   236

   237

/* A helper function... */

   238

bool visit_expression_type_c::is_ANY_SAFEDATE_type(symbol_c *type_symbol) {

   239

  if (type_symbol == NULL) {return false;}

   240

  if (typeid(*type_symbol) == typeid(safedate_type_name_c)) {return true;}

   241

  if (typeid(*type_symbol) == typeid(safetod_type_name_c))  {return true;}

   242

  if (typeid(*type_symbol) == typeid(safedt_type_name_c))   {return true;}

   243

  return false;

   244

}

   245

   246

/* A helper function... */

   247

bool visit_expression_type_c::is_ANY_DATE_compatible(symbol_c *type_symbol) {

   248

  if (type_symbol == NULL) {return false;}

   249

  if (is_ANY_DATE_type    (type_symbol))              {return true;}

   250

  if (is_ANY_SAFEDATE_type(type_symbol))              {return true;}

   251

  return false;

   252

}

   253

   254

/* A helper function... */

   255

bool visit_expression_type_c::is_ANY_STRING_type(symbol_c *type_symbol) {

   256

  if (type_symbol == NULL) {return false;}

   257

  if (typeid(*type_symbol) == typeid(string_type_name_c)) {return true;}

   258

  if (typeid(*type_symbol) == typeid(wstring_type_name_c)) {return true;}

   259

// TODO literal_string ???

   260

  return false;

   261

}

   262

   263

/* A helper function... */

   264

bool visit_expression_type_c::is_ANY_SAFESTRING_type(symbol_c *type_symbol) {

   265

  if (type_symbol == NULL) {return false;}

   266

  if (typeid(*type_symbol) == typeid(safestring_type_name_c)) {return true;}

   267

  if (typeid(*type_symbol) == typeid(safewstring_type_name_c)) {return true;}

   268

  return false;

   269

}

   270

   271

/* A helper function... */

   272

bool visit_expression_type_c::is_ANY_STRING_compatible(symbol_c *type_symbol) {

   273

  if (type_symbol == NULL) {return false;}

   274

  if (is_ANY_STRING_type    (type_symbol))              {return true;}

   275

  if (is_ANY_SAFESTRING_type(type_symbol))              {return true;}

   276

  return false;

   277

}

   278

   279

/* A helper function... */

   280

bool visit_expression_type_c::is_ANY_INT_type(symbol_c *type_symbol) {

   281

  if (type_symbol == NULL) {return false;}

   282

  if (typeid(*type_symbol) == typeid(sint_type_name_c))  {return true;}

   283

  if (typeid(*type_symbol) == typeid(int_type_name_c))   {return true;}

   284

  if (typeid(*type_symbol) == typeid(dint_type_name_c))  {return true;}

   285

  if (typeid(*type_symbol) == typeid(lint_type_name_c))  {return true;}

   286

  if (typeid(*type_symbol) == typeid(usint_type_name_c)) {return true;}

   287

  if (typeid(*type_symbol) == typeid(uint_type_name_c))  {return true;}

   288

  if (typeid(*type_symbol) == typeid(udint_type_name_c)) {return true;}

   289

  if (typeid(*type_symbol) == typeid(ulint_type_name_c)) {return true;}

   290

  return false;

   291

}

   292

   293

/* A helper function... */

   294

bool visit_expression_type_c::is_ANY_SAFEINT_type(symbol_c *type_symbol) {

   295

  if (type_symbol == NULL) {return false;}

   296

  if (typeid(*type_symbol) == typeid(safesint_type_name_c))  {return true;}

   297

  if (typeid(*type_symbol) == typeid(safeint_type_name_c))   {return true;}

   298

  if (typeid(*type_symbol) == typeid(safedint_type_name_c))  {return true;}

   299

  if (typeid(*type_symbol) == typeid(safelint_type_name_c))  {return true;}

   300

  if (typeid(*type_symbol) == typeid(safeusint_type_name_c)) {return true;}

   301

  if (typeid(*type_symbol) == typeid(safeuint_type_name_c))  {return true;}

   302

  if (typeid(*type_symbol) == typeid(safeudint_type_name_c)) {return true;}

   303

  if (typeid(*type_symbol) == typeid(safeulint_type_name_c)) {return true;}

   304

  return false;

   305

}

   306

   307

/* A helper function... */

   308

bool visit_expression_type_c::is_ANY_INT_compatible(symbol_c *type_symbol) {

   309

  if (type_symbol == NULL) {return false;}

   310

  if (is_ANY_INT_type    (type_symbol))              {return true;}

   311

  if (is_ANY_SAFEINT_type(type_symbol))              {return true;}

   312

  if (is_literal_integer_type(type_symbol))          {return true;}

   313

  return false;

   314

}

   315

   316

/* A helper function... */

   317

bool visit_expression_type_c::is_ANY_REAL_type(symbol_c *type_symbol) {

   318

  if (type_symbol == NULL) {return false;}

   319

  if (typeid(*type_symbol) == typeid(real_type_name_c))  {return true;}

   320

  if (typeid(*type_symbol) == typeid(lreal_type_name_c)) {return true;}

   321

  return false;

   322

}

   323

   324

/* A helper function... */

   325

bool visit_expression_type_c::is_ANY_SAFEREAL_type(symbol_c *type_symbol) {

   326

  if (type_symbol == NULL) {return false;}

   327

  if (typeid(*type_symbol) == typeid(safereal_type_name_c))  {return true;}

   328

  if (typeid(*type_symbol) == typeid(safelreal_type_name_c)) {return true;}

   329

  return false;

   330

}

   331

   332

/* A helper function... */

   333

bool visit_expression_type_c::is_ANY_REAL_compatible(symbol_c *type_symbol) {

   334

  if (type_symbol == NULL) {return false;}

   335

  if (is_ANY_REAL_type    (type_symbol))              {return true;}

   336

  if (is_ANY_SAFEREAL_type(type_symbol))              {return true;}

   337

  if (is_literal_real_type(type_symbol))              {return true;}

   338

  return false;

   339

}

   340

   341

/* A helper function... */

   342

bool visit_expression_type_c::is_ANY_BIT_type(symbol_c *type_symbol) {

   343

  if (type_symbol == NULL) {return false;}

   344

  if (typeid(*type_symbol) == typeid(bool_type_name_c))     {return true;}

   345

  if (typeid(*type_symbol) == typeid(byte_type_name_c))     {return true;}

   346

  if (typeid(*type_symbol) == typeid(word_type_name_c))     {return true;}

   347

  if (typeid(*type_symbol) == typeid(dword_type_name_c))    {return true;}

   348

  if (typeid(*type_symbol) == typeid(lword_type_name_c))    {return true;}

   349

  return false;

   350

}

   351

   352

/* A helper function... */

   353

bool visit_expression_type_c::is_ANY_SAFEBIT_type(symbol_c *type_symbol) {

   354

  if (type_symbol == NULL) {return false;}

   355

  if (typeid(*type_symbol) == typeid(safebool_type_name_c))     {return true;}

   356

  if (typeid(*type_symbol) == typeid(safebyte_type_name_c))     {return true;}

   357

  if (typeid(*type_symbol) == typeid(safeword_type_name_c))     {return true;}

   358

  if (typeid(*type_symbol) == typeid(safedword_type_name_c))    {return true;}

   359

  if (typeid(*type_symbol) == typeid(safelword_type_name_c))    {return true;}

   360

  return false;

   361

}

   362

   363

/* A helper function... */

   364

bool visit_expression_type_c::is_ANY_BIT_compatible(symbol_c *type_symbol) {

   365

  if (type_symbol == NULL) {return false;}

   366

  if (is_ANY_BIT_type    (type_symbol))              {return true;}

   367

  if (is_ANY_SAFEBIT_type(type_symbol))              {return true;}

   368

  if (is_nonneg_literal_integer_type(type_symbol))   {return true;}

   369

  if (is_literal_bool_type(type_symbol))             {return true;}

   370

  return false;

   371

}

   372

   373

/* A helper function... */

   374

bool visit_expression_type_c::is_BOOL_type(symbol_c *type_symbol) {

   375

  if (type_symbol == NULL) {return false;}

   376

  if (typeid(*type_symbol) == typeid(bool_type_name_c))      {return true;}

   377

  return false;

   378

}

   379

   380

/* A helper function... */

   381

bool visit_expression_type_c::is_SAFEBOOL_type(symbol_c *type_symbol){

   382

  if (type_symbol == NULL) {return false;}

   383

  if (typeid(*type_symbol) == typeid(safebool_type_name_c))  {return true;}

   384

  return false;  

   385

}

   386

   387

/* A helper function... */

   388

bool visit_expression_type_c::is_ANY_BOOL_compatible(symbol_c *type_symbol) {

   389

  if (type_symbol == NULL) {return false;}

   390

  if (is_BOOL_type    (type_symbol))              {return true;}

   391

  if (is_SAFEBOOL_type(type_symbol))              {return true;}

   392

  if (is_literal_bool_type(type_symbol))              {return true;}

   393

  return false;

   394

}

   395

   396

   397

#define is_type(type_name_symbol, type_name_class)  ((type_name_symbol == NULL) ? false : (typeid(*type_name_symbol) == typeid(type_name_class)))

   398

   399

   400

#define sizeoftype(symbol) get_sizeof_datatype_c::getsize(symbol)

   401

   402

   403

/* A helper function... */

   404

bool visit_expression_type_c::is_literal_integer_type(symbol_c *type_symbol) {

   405

  if (type_symbol == NULL) {return false;}

   406

  if (typeid(*type_symbol) == typeid(neg_integer_c))        {return true;}

   407

  return is_nonneg_literal_integer_type(type_symbol);

   408

}

   409

   410

   411

/* A helper function... */

   412

bool visit_expression_type_c::is_nonneg_literal_integer_type(symbol_c *type_symbol) {

   413

  if (type_symbol == NULL) {return false;}

   414

  if (typeid(*type_symbol) == typeid(integer_c))        {return true;}

   415

  if (typeid(*type_symbol) == typeid(binary_integer_c)) {return true;}

   416

  if (typeid(*type_symbol) == typeid(octal_integer_c))  {return true;}

   417

  if (typeid(*type_symbol) == typeid(hex_integer_c))    {return true;}

   418

  return false;

   419

}

   420

   421

   422

/* A helper function... */

   423

bool visit_expression_type_c::is_literal_real_type(symbol_c *type_symbol) {

   424

  if (type_symbol == NULL) {return false;}

   425

  if (typeid(*type_symbol) == typeid(real_c))     {return true;}

   426

  if (typeid(*type_symbol) == typeid(neg_real_c)) {return true;}

   427

  return false;

   428

}

   429

   430

   431

/* A helper function... */

   432

bool visit_expression_type_c::is_literal_bool_type(symbol_c *type_symbol) {

   433

  bool_type_name_c bool_t;

   434

   435

  if (type_symbol == NULL) {return false;}

   436

  if (typeid(*type_symbol) == typeid(boolean_true_c))    {return true;}

   437

  if (typeid(*type_symbol) == typeid(boolean_false_c))   {return true;}

   438

  if (is_nonneg_literal_integer_type(type_symbol))

   439

    if (sizeoftype(&bool_t) >= sizeoftype(type_symbol))  {return true;}

   440

  return false;

   441

}

   442

   450

/* Determine the common data type between two data types.

   451

 * If no common data type found, return NULL.

   452

 *

   453

 * If data types are identical, return the first (actually any would do...).

   454

 * If any of the data types is a literal, we confirm that 

   455

 *   the literal uses less bits than the fixed size data type.

   456

 *   e.g. BYTE and 1024 returns NULL

   457

 *        BYTE and 255  returns BYTE

   458

 *

   459

 * If two literals, then return the literal that requires more bits...

   460

 */

   461

   462

symbol_c *visit_expression_type_c::common_type__(symbol_c *first_type, symbol_c *second_type) {

   463

  if (first_type == NULL && second_type == NULL) {return NULL;}

   464

  if (first_type == NULL)  {return second_type;}

   465

  if (second_type == NULL) {return first_type;}

   466

   467

  if (is_literal_integer_type(first_type) && is_literal_integer_type(second_type))

   468

    {return ((sizeoftype(first_type) > sizeoftype(second_type))? first_type:second_type);}

   469

   470

  if (is_literal_real_type(first_type) && is_literal_real_type(second_type))

   471

    {return ((sizeoftype(first_type) > sizeoftype(second_type))? first_type:second_type);}

   472

   473

  if (is_literal_bool_type(first_type) && is_literal_bool_type(second_type))

   474

    {return first_type;}

   475

   476

  /* The following check can only be made after the is_literal_XXXX checks */

   477

  /* When two literals of the same type, with identical typeid's are checked,

   478

   * we must return the one that occupies more bits... This is done above.

   479

   */

   480

  if (typeid(*first_type) == typeid(*second_type)) {return first_type;}

   481

   482

  /* NOTE Although a BOOL is also an ANY_BIT, we must check it explicitly since some

   483

   *       literal bool values are not literal integers...

   484

   */ 

   485

  if (is_BOOL_type(first_type)        && is_literal_bool_type(second_type))    {return first_type;}

   486

  if (is_BOOL_type(second_type)       && is_literal_bool_type(first_type))     {return second_type;}

   487

   488

  if (is_SAFEBOOL_type(first_type)    && is_literal_bool_type(second_type))    {return first_type;}

   489

  if (is_SAFEBOOL_type(second_type)   && is_literal_bool_type(first_type))     {return second_type;}

   490

   491

  if (is_SAFEBOOL_type(first_type)    && is_BOOL_type(second_type))            {return second_type;}

   492

  if (is_SAFEBOOL_type(second_type)   && is_BOOL_type(first_type))             {return first_type;}

   493

   494

  if (is_ANY_BIT_type(first_type)     && is_nonneg_literal_integer_type(second_type))

   495

    {return ((sizeoftype(first_type)  >= sizeoftype(second_type))? first_type :NULL);}

   496

  if (is_ANY_BIT_type(second_type)    && is_nonneg_literal_integer_type(first_type))

   497

    {return ((sizeoftype(second_type) >= sizeoftype(first_type)) ? second_type:NULL);}

   498

   499

  if (is_ANY_SAFEBIT_type(first_type)     && is_nonneg_literal_integer_type(second_type))

   500

    {return ((sizeoftype(first_type)  >= sizeoftype(second_type))? first_type :NULL);}

   501