gcc/cppexp.c

   1 /* Parse C expressions for cpplib.
   2    Copyright (C) 1987, 1992, 1994, 1995, 1997, 1998, 1999, 2000, 2001,
   3    2002 Free Software Foundation.
   4    Contributed by Per Bothner, 1994.
   5
   6 This program is free software; you can redistribute it and/or modify it
   7 under the terms of the GNU General Public License as published by the
   8 Free Software Foundation; either version 2, or (at your option) any
   9 later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program; if not, write to the Free Software
  18 Foundation, 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "cpplib.h"
  24 #include "cpphash.h"
  25
  26 /* Yield nonzero if adding two numbers with A's and B's signs can yield a
  27    number with SUM's sign, where A, B, and SUM are all C integers.  */
  28 #define possible_sum_sign(a, b, sum) ((((a) ^ (b)) | ~ ((a) ^ (sum))) < 0)
  29
  30 static void integer_overflow PARAMS ((cpp_reader *));
  31 static HOST_WIDEST_INT left_shift PARAMS ((cpp_reader *, HOST_WIDEST_INT,
  32                                            unsigned int,
  33                                            unsigned HOST_WIDEST_INT));
  34 static HOST_WIDEST_INT right_shift PARAMS ((cpp_reader *, HOST_WIDEST_INT,
  35                                             unsigned int,
  36                                             unsigned HOST_WIDEST_INT));
  37 static struct op parse_number PARAMS ((cpp_reader *, const cpp_token *));
  38 static struct op parse_defined PARAMS ((cpp_reader *));
  39 static struct op eval_token PARAMS ((cpp_reader *, const cpp_token *));
  40 static struct op *reduce PARAMS ((cpp_reader *, struct op *, enum cpp_ttype));
  41
  42 struct op
  43 {
  44   enum cpp_ttype op;
  45   uchar unsignedp;    /* True if value should be treated as unsigned.  */
  46   HOST_WIDEST_INT value; /* The value logically "right" of op.  */
  47 };
  48
  49 /* Token type abuse.  There is no "error" token, but we can't get
  50    comments in #if, so we can abuse that token type.  Similarly,
  51    create unary plus and minus operators.  */
  52 #define CPP_ERROR CPP_COMMENT
  53 #define CPP_UPLUS (CPP_LAST_CPP_OP + 1)
  54 #define CPP_UMINUS (CPP_LAST_CPP_OP + 2)
  55
  56 /* With -O2, gcc appears to produce nice code, moving the error
  57    message load and subsequent jump completely out of the main path.  */
  58 #define SYNTAX_ERROR(msgid) \
  59   do { cpp_error (pfile, DL_ERROR, msgid); goto syntax_error; } while(0)
  60 #define SYNTAX_ERROR2(msgid, arg) \
  61   do { cpp_error (pfile, DL_ERROR, msgid, arg); goto syntax_error; } while(0)
  62
  63 struct suffix
  64 {
  65   const unsigned char s[4];
  66   const unsigned char u;
  67   const unsigned char l;
  68 };
  69
  70 static const struct suffix vsuf_1[] = {
  71   { "u", 1, 0 }, { "U", 1, 0 },
  72   { "l", 0, 1 }, { "L", 0, 1 }
  73 };
  74
  75 static const struct suffix vsuf_2[] = {
  76   { "ul", 1, 1 }, { "UL", 1, 1 }, { "uL", 1, 1 }, { "Ul", 1, 1 },
  77   { "lu", 1, 1 }, { "LU", 1, 1 }, { "Lu", 1, 1 }, { "lU", 1, 1 },
  78   { "ll", 0, 2 }, { "LL", 0, 2 }
  79 };
  80
  81 static const struct suffix vsuf_3[] = {
  82   { "ull", 1, 2 }, { "ULL", 1, 2 }, { "uLL", 1, 2 }, { "Ull", 1, 2 },
  83   { "llu", 1, 2 }, { "LLU", 1, 2 }, { "LLu", 1, 2 }, { "llU", 1, 2 }
  84 };
  85
  86 /* Parse and convert what is presumably an integer in TOK.  Accepts
  87    decimal, hex, or octal with or without size suffixes.  Returned op
  88    is CPP_ERROR on error, otherwise it is a CPP_NUMBER.  */
  89 static struct op
  90 parse_number (pfile, tok)
  91      cpp_reader *pfile;
  92      const cpp_token *tok;
  93 {
  94   struct op op;
  95   const uchar *start = tok->val.str.text;
  96   const uchar *end = start + tok->val.str.len;
  97   const uchar *p = start;
  98   int c = 0, i, nsuff;
  99   unsigned HOST_WIDEST_INT n = 0, nd, MAX_over_base;
 100   int base = 10;
 101   int overflow = 0;
 102   int digit, largest_digit = 0;
 103   const struct suffix *sufftab;
 104
 105   op.unsignedp = 0;
 106
 107   if (p[0] == '0')
 108     {
 109       if (end - start >= 3 && (p[1] == 'x' || p[1] == 'X'))
 110         {
 111           p += 2;
 112           base = 16;
 113         }
 114       else
 115         {
 116           p += 1;
 117           base = 8;
 118         }
 119     }
 120
 121   /* Some buggy compilers (e.g. MPW C) seem to need both casts.  */
 122   MAX_over_base = (((unsigned HOST_WIDEST_INT) -1)
 123                    / ((unsigned HOST_WIDEST_INT) base));
 124
 125   for(; p < end; p++)
 126     {
 127       c = *p;
 128
 129       if (ISDIGIT (c)
 130           || (base == 16 && ISXDIGIT (c)))
 131         digit = hex_value (c);
 132       else
 133         break;
 134
 135       if (largest_digit < digit)
 136         largest_digit = digit;
 137       nd = n * base + digit;
 138       overflow |= MAX_over_base < n || nd < n;
 139       n = nd;
 140     }
 141
 142   if (p < end)
 143     {
 144       /* Check for a floating point constant.  Note that float constants
 145          with an exponent or suffix but no decimal point are technically
 146          invalid (C99 6.4.4.2) but accepted elsewhere.  */
 147       if ((c == '.' || c == 'F' || c == 'f')
 148           || (base == 10 && (c == 'E' || c == 'e')
 149               && p+1 < end && (p[1] == '+' || p[1] == '-'))
 150           || (base == 16 && (c == 'P' || c == 'p')
 151               && p+1 < end && (p[1] == '+' || p[1] == '-')))
 152         SYNTAX_ERROR ("floating point numbers are not valid in #if");
 153
 154       /* Determine the suffix. l means long, and u means unsigned.
 155          See the suffix tables, above.  */
 156       switch (end - p)
 157         {
 158         case 1: sufftab = vsuf_1; nsuff = ARRAY_SIZE (vsuf_1); break;
 159         case 2: sufftab = vsuf_2; nsuff = ARRAY_SIZE (vsuf_2); break;
 160         case 3: sufftab = vsuf_3; nsuff = ARRAY_SIZE (vsuf_3); break;
 161         default: goto invalid_suffix;
 162         }
 163
 164       for (i = 0; i < nsuff; i++)
 165         if (memcmp (p, sufftab[i].s, end - p) == 0)
 166           break;
 167       if (i == nsuff)
 168         goto invalid_suffix;
 169       op.unsignedp = sufftab[i].u;
 170
 171       if (CPP_WTRADITIONAL (pfile)
 172           && sufftab[i].u
 173           && ! cpp_sys_macro_p (pfile))
 174         cpp_error (pfile, DL_WARNING, "traditional C rejects the `U' suffix");
 175       if (sufftab[i].l == 2 && CPP_OPTION (pfile, pedantic)
 176           && ! CPP_OPTION (pfile, c99))
 177         cpp_error (pfile, DL_PEDWARN,
 178                    "too many 'l' suffixes in integer constant");
 179     }
 180
 181   if (base <= largest_digit)
 182     cpp_error (pfile, DL_PEDWARN,
 183                "integer constant contains digits beyond the radix");
 184
 185   if (overflow)
 186     cpp_error (pfile, DL_PEDWARN, "integer constant out of range");
 187
 188   /* If too big to be signed, consider it unsigned.  */
 189   else if ((HOST_WIDEST_INT) n < 0 && ! op.unsignedp)
 190     {
 191       if (base == 10)
 192         cpp_error (pfile, DL_WARNING,
 193                    "integer constant is so large that it is unsigned");
 194       op.unsignedp = 1;
 195     }
 196
 197   op.value = n;
 198   op.op = CPP_NUMBER;
 199   return op;
 200
 201  invalid_suffix:
 202   cpp_error (pfile, DL_ERROR, "invalid suffix '%.*s' on integer constant",
 203              (int) (end - p), p);
 204  syntax_error:
 205   op.op = CPP_ERROR;
 206   return op;
 207 }
 208
 209 /* Handle meeting "defined" in a preprocessor expression.  */
 210 static struct op
 211 parse_defined (pfile)
 212      cpp_reader *pfile;
 213 {
 214   int paren = 0;
 215   cpp_hashnode *node = 0;
 216   const cpp_token *token;
 217   struct op op;
 218   cpp_context *initial_context = pfile->context;
 219
 220   /* Don't expand macros.  */
 221   pfile->state.prevent_expansion++;
 222
 223   token = cpp_get_token (pfile);
 224   if (token->type == CPP_OPEN_PAREN)
 225     {
 226       paren = 1;
 227       token = cpp_get_token (pfile);
 228     }
 229
 230   if (token->type == CPP_NAME)
 231     {
 232       node = token->val.node;
 233       if (paren && cpp_get_token (pfile)->type != CPP_CLOSE_PAREN)
 234         {
 235           cpp_error (pfile, DL_ERROR, "missing ')' after \"defined\"");
 236           node = 0;
 237         }
 238     }
 239   else
 240     {
 241       cpp_error (pfile, DL_ERROR,
 242                  "operator \"defined\" requires an identifier");
 243       if (token->flags & NAMED_OP)
 244         {
 245           cpp_token op;
 246
 247           op.flags = 0;
 248           op.type = token->type;
 249           cpp_error (pfile, DL_ERROR,
 250                      "(\"%s\" is an alternative token for \"%s\" in C++)",
 251                      cpp_token_as_text (pfile, token),
 252                      cpp_token_as_text (pfile, &op));
 253         }
 254     }
 255
 256   if (!node)
 257     op.op = CPP_ERROR;
 258   else
 259     {
 260       if (pfile->context != initial_context)
 261         cpp_error (pfile, DL_WARNING,
 262                    "this use of \"defined\" may not be portable");
 263
 264       op.value = node->type == NT_MACRO;
 265       op.unsignedp = 0;
 266       op.op = CPP_NUMBER;
 267
 268       /* A possible controlling macro of the form #if !defined ().
 269          _cpp_parse_expr checks there was no other junk on the line.  */
 270       pfile->mi_ind_cmacro = node;
 271     }
 272
 273   pfile->state.prevent_expansion--;
 274   return op;
 275 }
 276
 277 /* Convert a token into a CPP_NUMBER (an interpreted preprocessing
 278    number or character constant, or the result of the "defined" or "#"
 279    operators), or CPP_ERROR on error.  */
 280 static struct op
 281 eval_token (pfile, token)
 282      cpp_reader *pfile;
 283      const cpp_token *token;
 284 {
 285   unsigned int temp;
 286   struct op op;
 287
 288   op.op = CPP_NUMBER;
 289   op.unsignedp = 0;
 290
 291   switch (token->type)
 292     {
 293     case CPP_NUMBER:
 294       return parse_number (pfile, token);
 295
 296     case CPP_WCHAR:
 297       op.unsignedp = WCHAR_UNSIGNED;
 298     case CPP_CHAR:              /* Always unsigned.  */
 299       op.value = cpp_interpret_charconst (pfile, token, 1, &temp);
 300       break;
 301
 302     case CPP_NAME:
 303       if (token->val.node == pfile->spec_nodes.n_defined)
 304         return parse_defined (pfile);
 305       else if (CPP_OPTION (pfile, cplusplus)
 306                && (token->val.node == pfile->spec_nodes.n_true
 307                    || token->val.node == pfile->spec_nodes.n_false))
 308         {
 309           op.value = (token->val.node == pfile->spec_nodes.n_true);
 310
 311           /* Warn about use of true or false in #if when pedantic
 312              and stdbool.h has not been included.  */
 313           if (CPP_PEDANTIC (pfile)
 314               && ! cpp_defined (pfile, DSC("__bool_true_false_are_defined")))
 315             cpp_error (pfile, DL_PEDWARN,
 316                        "ISO C++ does not permit \"%s\" in #if",
 317                        NODE_NAME (token->val.node));
 318         }
 319       else
 320         {
 321           op.value = 0;
 322           if (CPP_OPTION (pfile, warn_undef) && !pfile->state.skip_eval)
 323             cpp_error (pfile, DL_WARNING, "\"%s\" is not defined",
 324                        NODE_NAME (token->val.node));
 325         }
 326       break;
 327
 328     default: /* CPP_HASH */
 329       if (_cpp_test_assertion (pfile, &temp))
 330         op.op = CPP_ERROR;
 331       op.value = temp;
 332     }
 333
 334   return op;
 335 }
 336
 337 /* Warn if appropriate on overflow.  */
 338 static void
 339 integer_overflow (pfile)
 340      cpp_reader *pfile;
 341 {
 342   if (CPP_PEDANTIC (pfile))
 343     cpp_error (pfile, DL_PEDWARN,
 344                "integer overflow in preprocessor expression");
 345 }
 346
 347 /* Handle shifting A left by B bits.  UNSIGNEDP is non-zero if A is
 348    unsigned.  */
 349 static HOST_WIDEST_INT
 350 left_shift (pfile, a, unsignedp, b)
 351      cpp_reader *pfile;
 352      HOST_WIDEST_INT a;
 353      unsigned int unsignedp;
 354      unsigned HOST_WIDEST_INT b;
 355 {
 356   if (b >= HOST_BITS_PER_WIDEST_INT)
 357     {
 358       if (! unsignedp && a != 0)
 359         integer_overflow (pfile);
 360       return 0;
 361     }
 362   else if (unsignedp)
 363     return (unsigned HOST_WIDEST_INT) a << b;
 364   else
 365     {
 366       HOST_WIDEST_INT l = a << b;
 367       if (l >> b != a)
 368         integer_overflow (pfile);
 369       return l;
 370     }
 371 }
 372
 373 /* Handle shifting A right by B bits.  UNSIGNEDP is non-zero if A is
 374    unsigned.  */
 375 static HOST_WIDEST_INT
 376 right_shift (pfile, a, unsignedp, b)
 377      cpp_reader *pfile ATTRIBUTE_UNUSED;
 378      HOST_WIDEST_INT a;
 379      unsigned int unsignedp;
 380      unsigned HOST_WIDEST_INT b;
 381 {
 382   if (b >= HOST_BITS_PER_WIDEST_INT)
 383     return unsignedp ? 0 : a >> (HOST_BITS_PER_WIDEST_INT - 1);
 384   else if (unsignedp)
 385     return (unsigned HOST_WIDEST_INT) a >> b;
 386   else
 387     return a >> b;
 388 }
 389 \f
 390 /* Operator precedence and flags table.
 391
 392 After an operator is returned from the lexer, if it has priority less
 393 than the operator on the top of the stack, we reduce the stack by one
 394 operator and repeat the test.  Since equal priorities do not reduce,
 395 this is naturally right-associative.
 396
 397 We handle left-associative operators by decrementing the priority of
 398 just-lexed operators by one, but retaining the priority of operators
 399 already on the stack.
 400
 401 The remaining cases are '(' and ')'.  We handle '(' by skipping the
 402 reduction phase completely.  ')' is given lower priority than
 403 everything else, including '(', effectively forcing a reduction of the
 404 parenthesised expression.  If there is a matching '(', the routine
 405 reduce() exits immediately.  If the normal exit route sees a ')', then
 406 there cannot have been a matching '(' and an error message is output.
 407
 408 The parser assumes all shifted operators require a left operand unless
 409 the flag NO_L_OPERAND is set.  These semantics are automatic; any
 410 extra semantics need to be handled with operator-specific code.  */
 411
 412 /* Flags.  */
 413 #define NO_L_OPERAND    (1 << 0)
 414 #define LEFT_ASSOC      (1 << 1)
 415
 416 /* Operator to priority map.  Must be in the same order as the first
 417    N entries of enum cpp_ttype.  */
 418 static const struct operator
 419 {
 420   uchar prio;
 421   uchar flags;
 422 } optab[] =
 423 {
 424   /* EQ */              {0, 0},         /* Shouldn't happen.  */
 425   /* NOT */             {16, NO_L_OPERAND},
 426   /* GREATER */         {12, LEFT_ASSOC},
 427   /* LESS */            {12, LEFT_ASSOC},
 428   /* PLUS */            {14, LEFT_ASSOC},
 429   /* MINUS */           {14, LEFT_ASSOC},
 430   /* MULT */            {15, LEFT_ASSOC},
 431   /* DIV */             {15, LEFT_ASSOC},
 432   /* MOD */             {15, LEFT_ASSOC},
 433   /* AND */             {9, LEFT_ASSOC},
 434   /* OR */              {7, LEFT_ASSOC},
 435   /* XOR */             {8, LEFT_ASSOC},
 436   /* RSHIFT */          {13, LEFT_ASSOC},
 437   /* LSHIFT */          {13, LEFT_ASSOC},
 438   /* MIN */             {10, LEFT_ASSOC},       /* C++ specific */
 439   /* MAX */             {10, LEFT_ASSOC},       /* extensions */
 440
 441   /* COMPL */           {16, NO_L_OPERAND},
 442   /* AND_AND */         {6, LEFT_ASSOC},
 443   /* OR_OR */           {5, LEFT_ASSOC},
 444   /* QUERY */           {3, 0},
 445   /* COLON */           {4, LEFT_ASSOC},
 446   /* COMMA */           {2, LEFT_ASSOC},
 447   /* OPEN_PAREN */      {1, NO_L_OPERAND},
 448   /* CLOSE_PAREN */     {0, 0},
 449   /* EOF */             {0, 0},
 450   /* EQ_EQ */           {11, LEFT_ASSOC},
 451   /* NOT_EQ */          {11, LEFT_ASSOC},
 452   /* GREATER_EQ */      {12, LEFT_ASSOC},
 453   /* LESS_EQ */         {12, LEFT_ASSOC},
 454   /* UPLUS */           {16, NO_L_OPERAND},
 455   /* UMINUS */          {16, NO_L_OPERAND}
 456 };
 457
 458 #define COMPARE(OP) \
 459   top->unsignedp = 0; \
 460   top->value = (unsigned1 | unsigned2) \
 461   ? (unsigned HOST_WIDEST_INT) v1 OP (unsigned HOST_WIDEST_INT) v2 \
 462   : (v1 OP v2)
 463 #define EQUALITY(OP) \
 464   top->value = v1 OP v2; \
 465   top->unsignedp = 0;
 466 #define BITWISE(OP) \
 467   top->value = v1 OP v2; \
 468   top->unsignedp = unsigned1 | unsigned2;
 469 #define MINMAX(OP) \
 470   top->value = (v1 OP v2) ? v1 : v2; \
 471   top->unsignedp = unsigned1 | unsigned2;
 472 #define UNARY(OP) \
 473   top->value = OP v2; \
 474   top->unsignedp = unsigned2;
 475 #define SHIFT(PSH, MSH) \
 476   if (pfile->state.skip_eval)  \
 477     break;              \
 478   top->unsignedp = unsigned1; \
 479   if (v2 < 0 && ! unsigned2)  \
 480     top->value = MSH (pfile, v1, unsigned1, -v2); \
 481   else \
 482     top->value = PSH (pfile, v1, unsigned1, v2);
 483
 484 /* Parse and evaluate a C expression, reading from PFILE.
 485    Returns the truth value of the expression.
 486
 487    The implementation is an operator precedence parser, i.e. a
 488    bottom-up parser, using a stack for not-yet-reduced tokens.
 489
 490    The stack base is op_stack, and the current stack pointer is 'top'.
 491    There is a stack element for each operator (only), and the most
 492    recently pushed operator is 'top->op'.  An operand (value) is
 493    stored in the 'value' field of the stack element of the operator
 494    that precedes it.  */
 495 bool
 496 _cpp_parse_expr (pfile)
 497      cpp_reader *pfile;
 498 {
 499   struct op *top = pfile->op_stack;
 500   const cpp_token *token = NULL, *prev_token;
 501   unsigned int lex_count;
 502   bool saw_leading_not, want_value = true;
 503
 504   pfile->state.skip_eval = 0;
 505
 506   /* Set up detection of #if ! defined().  */
 507   pfile->mi_ind_cmacro = 0;
 508   saw_leading_not = false;
 509   lex_count = 0;
 510
 511   /* Lowest priority operator prevents further reductions.  */
 512   top->op = CPP_EOF;
 513
 514   for (;;)
 515     {
 516       struct op op;
 517
 518       prev_token = token;
 519       token = cpp_get_token (pfile);
 520       lex_count++;
 521       op.op = token->type;
 522
 523       switch (op.op)
 524         {
 525           /* These tokens convert into values.  */
 526         case CPP_NUMBER:
 527         case CPP_CHAR:
 528         case CPP_WCHAR:
 529         case CPP_NAME:
 530         case CPP_HASH:
 531           if (!want_value)
 532             SYNTAX_ERROR2 ("missing binary operator before token \"%s\"",
 533                            cpp_token_as_text (pfile, token));
 534           want_value = false;
 535           op = eval_token (pfile, token);
 536           if (op.op == CPP_ERROR)
 537             goto syntax_error;
 538           top->value = op.value;
 539           top->unsignedp = op.unsignedp;
 540           continue;
 541
 542         case CPP_NOT:
 543           saw_leading_not = lex_count == 1;
 544           break;
 545         case CPP_PLUS:
 546           if (want_value)
 547             op.op = CPP_UPLUS;
 548           break;
 549         case CPP_MINUS:
 550           if (want_value)
 551             op.op = CPP_UMINUS;
 552           break;
 553         case CPP_OTHER:
 554           if (ISGRAPH (token->val.c))
 555             SYNTAX_ERROR2 ("invalid character '%c' in #if", token->val.c);
 556           else
 557             SYNTAX_ERROR2 ("invalid character '\\%03o' in #if", token->val.c);
 558
 559         default:
 560           if ((int) op.op <= (int) CPP_EQ || (int) op.op >= (int) CPP_PLUS_EQ)
 561             SYNTAX_ERROR2 ("token \"%s\" is not valid in #if expressions",
 562                            cpp_token_as_text (pfile, token));
 563           break;
 564         }
 565
 566       /* Check we have a value or operator as appropriate.  */
 567       if (optab[op.op].flags & NO_L_OPERAND)
 568         {
 569           if (!want_value)
 570             SYNTAX_ERROR2 ("missing binary operator before token \"%s\"",
 571                            cpp_token_as_text (pfile, token));
 572         }
 573       else if (want_value)
 574         {
 575           /* Ordering here is subtle and intended to favour the
 576              missing parenthesis diagnostics over alternatives.  */
 577           if (op.op == CPP_CLOSE_PAREN)
 578             {
 579               if (top->op == CPP_OPEN_PAREN)
 580                 SYNTAX_ERROR ("void expression between '(' and ')'");
 581             }
 582           else if (top->op == CPP_EOF)
 583             SYNTAX_ERROR ("#if with no expression");
 584           if (top->op != CPP_EOF && top->op != CPP_OPEN_PAREN)
 585             SYNTAX_ERROR2 ("operator '%s' has no right operand",
 586                            cpp_token_as_text (pfile, prev_token));
 587         }
 588
 589       top = reduce (pfile, top, op.op);
 590       if (!top)
 591         goto syntax_error;
 592
 593       if (op.op == CPP_EOF)
 594         break;
 595
 596       switch (op.op)
 597         {
 598         case CPP_CLOSE_PAREN:
 599           continue;
 600         case CPP_OR_OR:
 601           if (top->value)
 602             pfile->state.skip_eval++;
 603           break;
 604         case CPP_AND_AND:
 605         case CPP_QUERY:
 606           if (!top->value)
 607             pfile->state.skip_eval++;
 608           break;
 609         case CPP_COLON:
 610           if (top->op != CPP_QUERY)
 611             SYNTAX_ERROR (" ':' without preceding '?'");
 612           if (top[-1].value) /* Was '?' condition true?  */
 613             pfile->state.skip_eval++;
 614           else
 615             pfile->state.skip_eval--;
 616         default:
 617           break;
 618         }
 619
 620       want_value = true;
 621
 622       /* Check for and handle stack overflow.  */
 623       if (++top == pfile->op_limit)
 624         top = _cpp_expand_op_stack (pfile);
 625
 626       top->op = op.op;
 627     }
 628
 629   /* The controlling macro expression is only valid if we called lex 3
 630      times: <!> <defined expression> and <EOF>.  push_conditional ()
 631      checks that we are at top-of-file.  */
 632   if (pfile->mi_ind_cmacro && !(saw_leading_not && lex_count == 3))
 633     pfile->mi_ind_cmacro = 0;
 634
 635   if (top != pfile->op_stack)
 636     {
 637       cpp_error (pfile, DL_ICE, "unbalanced stack in #if");
 638     syntax_error:
 639       return false;  /* Return false on syntax error.  */
 640     }
 641
 642   return top->value != 0;
 643 }
 644
 645 /* Reduce the operator / value stack if possible, in preparation for
 646    pushing operator OP.  Returns NULL on error, otherwise the top of
 647    the stack.  */
 648 static struct op *
 649 reduce (pfile, top, op)
 650      cpp_reader *pfile;
 651      struct op *top;
 652      enum cpp_ttype op;
 653 {
 654   unsigned int prio;
 655
 656   if (op == CPP_OPEN_PAREN)
 657     return top;
 658
 659   /* Decrement the priority of left-associative operators to force a
 660      reduction with operators of otherwise equal priority.  */
 661   prio = optab[op].prio - ((optab[op].flags & LEFT_ASSOC) != 0);
 662   while (prio < optab[top->op].prio)
 663     {
 664       HOST_WIDEST_INT v1, v2;
 665       unsigned int unsigned1, unsigned2;
 666
 667       unsigned2 = top->unsignedp, v2 = top->value;
 668       top--;
 669       unsigned1 = top->unsignedp, v1 = top->value;
 670
 671       /* Now set top->value = (top[1].op)(v1, v2); */
 672       switch (top[1].op)
 673         {
 674         default:
 675           cpp_error (pfile, DL_ICE, "impossible operator '%u'", top[1].op);
 676           return 0;
 677
 678         case CPP_NOT:    UNARY(!);      break;
 679         case CPP_COMPL:  UNARY(~);      break;
 680         case CPP_LESS:   COMPARE(<);    break;
 681         case CPP_GREATER: COMPARE(>);   break;
 682         case CPP_LESS_EQ: COMPARE(<=);  break;
 683         case CPP_GREATER_EQ: COMPARE(>=); break;
 684         case CPP_EQ_EQ:  EQUALITY(==);  break;
 685         case CPP_NOT_EQ: EQUALITY(!=);  break;
 686         case CPP_AND:    BITWISE(&);    break;
 687         case CPP_XOR:    BITWISE(^);    break;
 688         case CPP_OR:     BITWISE(|);    break;
 689         case CPP_LSHIFT: SHIFT(left_shift, right_shift); break;
 690         case CPP_RSHIFT: SHIFT(right_shift, left_shift); break;
 691         case CPP_MIN:    MINMAX(<);     break;
 692         case CPP_MAX:    MINMAX(>);     break;
 693
 694         case CPP_UPLUS:
 695           /* Can't use UNARY(+) because K+R C did not have unary
 696              plus.  Can't use UNARY() because some compilers object
 697              to the empty argument.  */
 698           top->value = v2;
 699           top->unsignedp = unsigned2;
 700           if (CPP_WTRADITIONAL (pfile))
 701             cpp_error (pfile, DL_WARNING,
 702                        "traditional C rejects the unary plus operator");
 703           break;
 704         case CPP_UMINUS:
 705           UNARY(-);
 706           if (!pfile->state.skip_eval && (top->value & v2) < 0 && !unsigned2)
 707             integer_overflow (pfile);
 708           break;
 709
 710         case CPP_PLUS:
 711           top->value = v1 + v2;
 712           top->unsignedp = unsigned1 | unsigned2;
 713           if (! top->unsignedp && ! pfile->state.skip_eval
 714               && ! possible_sum_sign (v1, v2, top->value))
 715             integer_overflow (pfile);
 716           break;
 717         case CPP_MINUS:
 718           top->value = v1 - v2;
 719           top->unsignedp = unsigned1 | unsigned2;
 720           if (! top->unsignedp && ! pfile->state.skip_eval
 721               && ! possible_sum_sign (top->value, v2, v1))
 722             integer_overflow (pfile);
 723           break;
 724         case CPP_MULT:
 725           top->unsignedp = unsigned1 | unsigned2;
 726           if (top->unsignedp)
 727             top->value = (unsigned HOST_WIDEST_INT) v1 * v2;
 728           else if (!pfile->state.skip_eval)
 729             {
 730               top->value = v1 * v2;
 731               if (v1 && (top->value / v1 != v2
 732                          || (top->value & v1 & v2) < 0))
 733                 integer_overflow (pfile);
 734             }
 735           break;
 736         case CPP_DIV:
 737         case CPP_MOD:
 738           if (pfile->state.skip_eval)
 739             break;
 740           if (v2 == 0)
 741             {
 742               cpp_error (pfile, DL_ERROR, "division by zero in #if");
 743               return 0;
 744             }
 745           top->unsignedp = unsigned1 | unsigned2;
 746           if (top[1].op == CPP_DIV)
 747             {
 748               if (top->unsignedp)
 749                 top->value = (unsigned HOST_WIDEST_INT) v1 / v2;
 750               else
 751                 {
 752                   top->value = v1 / v2;
 753                   if ((top->value & v1 & v2) < 0)
 754                     integer_overflow (pfile);
 755                 }
 756             }
 757           else
 758             {
 759               if (top->unsignedp)
 760                 top->value = (unsigned HOST_WIDEST_INT) v1 % v2;
 761               else
 762                 top->value = v1 % v2;
 763             }
 764           break;
 765
 766         case CPP_OR_OR:
 767           top->value = v1 || v2;
 768           top->unsignedp = 0;
 769           if (v1) pfile->state.skip_eval--;
 770           break;
 771         case CPP_AND_AND:
 772           top->value = v1 && v2;
 773           top->unsignedp = 0;
 774           if (!v1) pfile->state.skip_eval--;
 775           break;
 776         case CPP_COMMA:
 777           if (CPP_PEDANTIC (pfile))
 778             cpp_error (pfile, DL_PEDWARN,
 779                        "comma operator in operand of #if");
 780           top->value = v2;
 781           top->unsignedp = unsigned2;
 782           break;
 783         case CPP_QUERY:
 784           cpp_error (pfile, DL_ERROR, "'?' without following ':'");
 785           return 0;
 786         case CPP_COLON:
 787           top--;
 788           if (top->value) pfile->state.skip_eval--;
 789           top->value = top->value ? v1 : v2;
 790           top->unsignedp = unsigned1 | unsigned2;
 791           break;
 792         case CPP_OPEN_PAREN:
 793           if (op != CPP_CLOSE_PAREN)
 794             {
 795               cpp_error (pfile, DL_ERROR, "missing ')' in expression");
 796               return 0;
 797             }
 798           top->value = v2;
 799           top->unsignedp = unsigned2;
 800           return top;
 801         }
 802     }
 803
 804   if (op == CPP_CLOSE_PAREN)
 805     {
 806       cpp_error (pfile, DL_ERROR, "missing '(' in expression");
 807       return 0;
 808     }
 809
 810   return top;
 811 }
 812
 813 /* Returns the position of the old top of stack after expansion.  */
 814 struct op *
 815 _cpp_expand_op_stack (pfile)
 816      cpp_reader *pfile;
 817 {
 818   size_t n = (size_t) (pfile->op_limit - pfile->op_stack);
 819
 820   pfile->op_stack = (struct op *) xrealloc (pfile->op_stack,
 821                                             (n * 2 + 20) * sizeof (struct op));
 822
 823   return pfile->op_stack + n;
 824 }