gcc/cppexp.c

   1 /* Parse C expressions for CCCP.
   2    Copyright (C) 1987, 92, 94, 95, 97, 98, 1999 Free Software Foundation.
   3
   4 This program is free software; you can redistribute it and/or modify it
   5 under the terms of the GNU General Public License as published by the
   6 Free Software Foundation; either version 2, or (at your option) any
   7 later version.
   8
   9 This program is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 GNU General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with this program; if not, write to the Free Software
  16 Foundation, 59 Temple Place - Suite 330,
  17 Boston, MA 02111-1307, USA.
  18
  19  In other words, you are welcome to use, share and improve this program.
  20  You are forbidden to forbid anyone else to use, share and improve
  21  what you give them.   Help stamp out software-hoarding!
  22
  23 Written by Per Bothner 1994.  */
  24
  25 /* Parse a C expression from text in a string  */
  26
  27 #include "config.h"
  28 #include "system.h"
  29 #include "cpplib.h"
  30
  31 #ifdef MULTIBYTE_CHARS
  32 #include <locale.h>
  33 #endif
  34
  35 #ifndef CHAR_TYPE_SIZE
  36 #define CHAR_TYPE_SIZE BITS_PER_UNIT
  37 #endif
  38
  39 #ifndef INT_TYPE_SIZE
  40 #define INT_TYPE_SIZE BITS_PER_WORD
  41 #endif
  42
  43 #ifndef LONG_TYPE_SIZE
  44 #define LONG_TYPE_SIZE BITS_PER_WORD
  45 #endif
  46
  47 #ifndef WCHAR_TYPE_SIZE
  48 #define WCHAR_TYPE_SIZE INT_TYPE_SIZE
  49 #endif
  50
  51 #ifndef MAX_CHAR_TYPE_SIZE
  52 #define MAX_CHAR_TYPE_SIZE CHAR_TYPE_SIZE
  53 #endif
  54
  55 #ifndef MAX_INT_TYPE_SIZE
  56 #define MAX_INT_TYPE_SIZE INT_TYPE_SIZE
  57 #endif
  58
  59 #ifndef MAX_LONG_TYPE_SIZE
  60 #define MAX_LONG_TYPE_SIZE LONG_TYPE_SIZE
  61 #endif
  62
  63 #ifndef MAX_WCHAR_TYPE_SIZE
  64 #define MAX_WCHAR_TYPE_SIZE WCHAR_TYPE_SIZE
  65 #endif
  66
  67 #define MAX_CHAR_TYPE_MASK (MAX_CHAR_TYPE_SIZE < HOST_BITS_PER_WIDEST_INT \
  68                             ? (~ (~ (HOST_WIDEST_INT) 0 << MAX_CHAR_TYPE_SIZE)) \
  69                             : ~ (HOST_WIDEST_INT) 0)
  70
  71 #define MAX_WCHAR_TYPE_MASK (MAX_WCHAR_TYPE_SIZE < HOST_BITS_PER_WIDEST_INT \
  72                              ? ~ (~ (HOST_WIDEST_INT) 0 << MAX_WCHAR_TYPE_SIZE) \
  73                              : ~ (HOST_WIDEST_INT) 0)
  74
  75 /* Yield nonzero if adding two numbers with A's and B's signs can yield a
  76    number with SUM's sign, where A, B, and SUM are all C integers.  */
  77 #define possible_sum_sign(a, b, sum) ((((a) ^ (b)) | ~ ((a) ^ (sum))) < 0)
  78
  79 static void integer_overflow PARAMS ((cpp_reader *));
  80 static HOST_WIDEST_INT left_shift PARAMS ((cpp_reader *, HOST_WIDEST_INT, int, unsigned HOST_WIDEST_INT));
  81 static HOST_WIDEST_INT right_shift PARAMS ((cpp_reader *, HOST_WIDEST_INT, int, unsigned HOST_WIDEST_INT));
  82
  83 #define ERROR 299
  84 #define OROR 300
  85 #define ANDAND 301
  86 #define EQUAL 302
  87 #define NOTEQUAL 303
  88 #define LEQ 304
  89 #define GEQ 305
  90 #define LSH 306
  91 #define RSH 307
  92 #define NAME 308
  93 #define INT 309
  94 #define CHAR 310
  95
  96 #define LEFT_OPERAND_REQUIRED 1
  97 #define RIGHT_OPERAND_REQUIRED 2
  98 #define HAVE_VALUE 4
  99 /* SKIP_OPERAND is set for '&&' '||' '?' and ':' when the
 100    following operand should be short-circuited instead of evaluated.  */
 101 #define SKIP_OPERAND 8
 102 /*#define UNSIGNEDP 16*/
 103
 104 #define SKIP_WHITE_SPACE(p) do { while (is_hor_space[*p]) p++; } while (0)
 105
 106 struct operation {
 107     short op;
 108     char rprio; /* Priority of op (relative to it right operand).  */
 109     char flags;
 110     char unsignedp;    /* true if value should be treated as unsigned */
 111     HOST_WIDEST_INT value;        /* The value logically "right" of op.  */
 112 };
 113
 114 /* Parse and convert an integer for #if.  Accepts decimal, hex, or octal
 115    with or without size suffixes.  */
 116
 117 static struct operation
 118 parse_number (pfile, start, end)
 119      cpp_reader *pfile;
 120      U_CHAR *start;
 121      U_CHAR *end;
 122 {
 123   struct operation op;
 124   U_CHAR *p = start;
 125   int c;
 126   unsigned HOST_WIDEST_INT n = 0, nd, MAX_over_base;
 127   int base = 10;
 128   int overflow = 0;
 129   int digit, largest_digit = 0;
 130   int spec_long = 0;
 131
 132   op.unsignedp = 0;
 133
 134   if (p[0] == '0')
 135     {
 136       if (end - start >= 3 && (p[1] == 'x' || p[1] == 'X'))
 137         {
 138           p += 2;
 139           base = 16;
 140         }
 141       else
 142         {
 143           p += 1;
 144           base = 8;
 145         }
 146     }
 147
 148   /* Some buggy compilers (e.g. MPW C) seem to need both casts.  */
 149   MAX_over_base = (((unsigned HOST_WIDEST_INT) -1)
 150                    / ((unsigned HOST_WIDEST_INT) base));
 151
 152   while (p < end)
 153     {
 154       c = *p++;
 155
 156       if (c >= '0' && c <= '9')
 157         digit = c - '0';
 158       else if (base == 16 && c >= 'a' && c <= 'f') /* FIXME: assumes ASCII */
 159         digit = c - 'a' + 10;
 160       else if (base == 16 && c >= 'A' && c <= 'F')
 161         digit = c - 'A' + 10;
 162       else if (c == '.')
 163         {
 164           /* It's a float since it contains a point.  */
 165           cpp_error (pfile,
 166                 "floating point numbers are not allowed in #if expressions");
 167           goto error;
 168         }
 169       else
 170         {
 171           /* `l' means long, and `u' means unsigned.  */
 172           for (;;)
 173             {
 174               if (c == 'l' || c == 'L')
 175                   spec_long++;
 176               else if (c == 'u' || c == 'U')
 177                   op.unsignedp++;
 178               else
 179                 {
 180                   /* Decrement p here so that the error for an invalid number
 181                      will be generated below in the case where this is the
 182                      last character in the buffer.  */
 183                   p--;
 184                   break;
 185                 }
 186               if (p == end)
 187                 break;
 188               c = *p++;
 189             }
 190           /* Don't look for any more digits after the suffixes.  */
 191           break;
 192         }
 193
 194       if (largest_digit < digit)
 195         largest_digit = digit;
 196       nd = n * base + digit;
 197       overflow |= MAX_over_base < n || nd < n;
 198       n = nd;
 199     }
 200
 201   if (p != end)
 202     {
 203       cpp_error (pfile, "invalid number in #if expression");
 204       goto error;
 205     }
 206   else if (spec_long > (CPP_OPTIONS (pfile)->c89 ? 1 : 2))
 207     {
 208       cpp_error (pfile, "too many `l' suffixes in integer constant");
 209       goto error;
 210     }
 211   else if (op.unsignedp > 1)
 212     {
 213       cpp_error (pfile, "too many `u' suffixes in integer constant");
 214       goto error;
 215     }
 216
 217   if (base <= largest_digit)
 218     cpp_pedwarn (pfile, "integer constant contains digits beyond the radix");
 219
 220   if (overflow)
 221     cpp_pedwarn (pfile, "integer constant out of range");
 222
 223   /* If too big to be signed, consider it unsigned.  */
 224   else if ((HOST_WIDEST_INT) n < 0 && ! op.unsignedp)
 225     {
 226       if (base == 10)
 227         cpp_warning (pfile,
 228                      "integer constant is so large that it is unsigned");
 229       op.unsignedp = 1;
 230     }
 231
 232   op.value = n;
 233   op.op = INT;
 234   return op;
 235
 236  error:
 237   op.op = ERROR;
 238   return op;
 239 }
 240
 241 /* Parse and convert a character constant for #if.  Understands backslash
 242    escapes (\n, \031) and multibyte characters (if so configured).  */
 243 static struct operation
 244 parse_charconst (pfile, start, end)
 245      cpp_reader *pfile;
 246      U_CHAR *start;
 247      U_CHAR *end;
 248 {
 249   struct operation op;
 250   HOST_WIDEST_INT result = 0;
 251   int num_chars = 0;
 252   int num_bits;
 253   unsigned int width = MAX_CHAR_TYPE_SIZE, mask = MAX_CHAR_TYPE_MASK;
 254   int max_chars;
 255   U_CHAR *ptr = start;
 256
 257   /* FIXME: Should use reentrant multibyte functions.  */
 258 #ifdef MULTIBYTE_CHARS
 259   wchar_t c;
 260   (void) mbtowc (NULL_PTR, NULL_PTR, 0);
 261 #else
 262   int c;
 263 #endif
 264
 265   if (*ptr == 'L')
 266     {
 267       ++ptr;
 268       width = MAX_WCHAR_TYPE_SIZE, mask = MAX_WCHAR_TYPE_MASK;
 269     }
 270   max_chars = MAX_LONG_TYPE_SIZE / width;
 271
 272   ++ptr;  /* skip initial quote */
 273
 274   while (ptr < end)
 275     {
 276 #ifndef MULTIBYTE_CHARS
 277       c = *ptr++;
 278 #else
 279       ptr += mbtowc (&c, ptr, end - ptr);
 280 #endif
 281       if (c == '\'' || c == '\0')
 282         break;
 283       else if (c == '\\')
 284         {
 285           /* Hopefully valid assumption: if mbtowc returns a backslash,
 286              we are in initial shift state.  No valid escape-sequence
 287              character can take us out of initial shift state or begin
 288              an unshifted multibyte char, so cpp_parse_escape doesn't
 289              need to know about multibyte chars.  */
 290
 291           c = cpp_parse_escape (pfile, (char **) &ptr, mask);
 292           if (width < HOST_BITS_PER_INT
 293               && (unsigned int) c >= (unsigned int)(1 << width))
 294             cpp_pedwarn (pfile, "escape sequence out of range for character");
 295         }
 296
 297       /* Merge character into result; ignore excess chars.  */
 298       if (++num_chars <= max_chars)
 299         {
 300           if (width < HOST_BITS_PER_INT)
 301             result = (result << width) | (c & ((1 << width) - 1));
 302           else
 303             result = c;
 304         }
 305     }
 306
 307   if (num_chars == 0)
 308     {
 309       cpp_error (pfile, "empty character constant");
 310       goto error;
 311     }
 312   else if (c != '\'')
 313     {
 314       /* cpp_get_token has already emitted an error if !traditional. */
 315       if (! CPP_TRADITIONAL (pfile))
 316         cpp_error (pfile, "malformatted character constant");
 317       goto error;
 318     }
 319   else if (num_chars > max_chars)
 320     {
 321       cpp_error (pfile, "character constant too long");
 322       goto error;
 323     }
 324   else if (num_chars != 1 && ! CPP_TRADITIONAL (pfile))
 325     cpp_warning (pfile, "multi-character character constant");
 326
 327   /* If char type is signed, sign-extend the constant.  */
 328   num_bits = num_chars * width;
 329
 330   if (cpp_lookup (pfile, (U_CHAR *)"__CHAR_UNSIGNED__",
 331                   sizeof ("__CHAR_UNSIGNED__")-1, -1)
 332       || ((result >> (num_bits - 1)) & 1) == 0)
 333     op.value = result & ((unsigned HOST_WIDEST_INT) ~0
 334                          >> (HOST_BITS_PER_WIDEST_INT - num_bits));
 335   else
 336     op.value = result | ~((unsigned HOST_WIDEST_INT) ~0
 337                           >> (HOST_BITS_PER_WIDEST_INT - num_bits));
 338
 339   /* This is always a signed type.  */
 340   op.unsignedp = 0;
 341   op.op = CHAR;
 342   return op;
 343
 344  error:
 345   op.op = ERROR;
 346   return op;
 347 }
 348
 349
 350 struct token {
 351   char *operator;
 352   int token;
 353 };
 354
 355 static struct token tokentab2[] = {
 356   {"&&", ANDAND},
 357   {"||", OROR},
 358   {"<<", LSH},
 359   {">>", RSH},
 360   {"==", EQUAL},
 361   {"!=", NOTEQUAL},
 362   {"<=", LEQ},
 363   {">=", GEQ},
 364   {"++", ERROR},
 365   {"--", ERROR},
 366   {NULL, ERROR}
 367 };
 368
 369 /* Read one token.  */
 370
 371 static struct operation
 372 cpp_lex (pfile, skip_evaluation)
 373      cpp_reader *pfile;
 374      int skip_evaluation;
 375 {
 376   U_CHAR c;
 377   struct token *toktab;
 378   enum cpp_token token;
 379   struct operation op;
 380   U_CHAR *tok_start, *tok_end;
 381   int old_written;
 382
 383  retry:
 384
 385   old_written = CPP_WRITTEN (pfile);
 386   cpp_skip_hspace (pfile);
 387   c = CPP_BUF_PEEK (CPP_BUFFER (pfile));
 388   if (c == '#')
 389     {
 390       op.op = INT;
 391       op.value = cpp_read_check_assertion (pfile);
 392       return op;
 393     }
 394
 395   if (c == '\n')
 396     {
 397       op.op = 0;
 398       return op;
 399     }
 400
 401   token = cpp_get_token (pfile);
 402   tok_start = pfile->token_buffer + old_written;
 403   tok_end = CPP_PWRITTEN (pfile);
 404   pfile->limit = tok_start;
 405   switch (token)
 406   {
 407     case CPP_EOF: /* Should not happen ...  */
 408     case CPP_VSPACE:
 409       op.op = 0;
 410       return op;
 411     case CPP_POP:
 412       if (CPP_BUFFER (pfile)->fname != NULL)
 413         {
 414           op.op = 0;
 415           return op;
 416         }
 417       cpp_pop_buffer (pfile);
 418       goto retry;
 419     case CPP_HSPACE:
 420     case CPP_COMMENT:
 421       goto retry;
 422     case CPP_NUMBER:
 423       return parse_number (pfile, tok_start, tok_end);
 424     case CPP_STRING:
 425       cpp_error (pfile, "string constants not allowed in #if expressions");
 426       op.op = ERROR;
 427       return op;
 428     case CPP_CHAR:
 429       return parse_charconst (pfile, tok_start, tok_end);
 430
 431     case CPP_NAME:
 432       op.op = INT;
 433       op.unsignedp = 0;
 434       op.value = 0;
 435       if (strcmp (tok_start, "defined"))
 436         {
 437           if (CPP_WARN_UNDEF (pfile) && !skip_evaluation)
 438             cpp_warning (pfile, "`%.*s' is not defined",
 439                          (int) (tok_end - tok_start), tok_start);
 440         }
 441       else
 442         {
 443           int paren = 0, len;
 444           cpp_buffer *ip = CPP_BUFFER (pfile);
 445           U_CHAR *tok;
 446
 447           SKIP_WHITE_SPACE (ip->cur);
 448           if (*ip->cur == '(')
 449             {
 450               paren++;
 451               ip->cur++;                        /* Skip over the paren */
 452               SKIP_WHITE_SPACE (ip->cur);
 453             }
 454
 455           if (!is_idstart[*ip->cur])
 456             goto oops;
 457           if (ip->cur[0] == 'L' && (ip->cur[1] == '\'' || ip->cur[1] == '"'))
 458             goto oops;
 459           tok = ip->cur;
 460           while (is_idchar[*ip->cur])
 461             ++ip->cur;
 462           len = ip->cur - tok;
 463           SKIP_WHITE_SPACE (ip->cur);
 464           if (paren)
 465             {
 466               if (*ip->cur != ')')
 467                 goto oops;
 468               ++ip->cur;
 469             }
 470           if (cpp_lookup (pfile, tok, len, -1))
 471             op.value = 1;
 472
 473         }
 474       return op;
 475
 476     oops:
 477       cpp_error (pfile, "`defined' without an identifier");
 478       return op;
 479
 480     case CPP_OTHER:
 481       /* See if it is a special token of length 2.  */
 482       if (tok_start + 2 == tok_end)
 483         {
 484           for (toktab = tokentab2; toktab->operator != NULL; toktab++)
 485             if (tok_start[0] == toktab->operator[0]
 486                 && tok_start[1] == toktab->operator[1])
 487                 break;
 488           if (toktab->token == ERROR)
 489             cpp_error (pfile, "`%s' not allowed in operand of `#if'",
 490                        tok_start);
 491           op.op = toktab->token;
 492           return op;
 493         }
 494       /* fall through */
 495     default:
 496       op.op = *tok_start;
 497       return op;
 498   }
 499 }
 500
 501
 502 /* Parse a C escape sequence.  STRING_PTR points to a variable
 503    containing a pointer to the string to parse.  That pointer
 504    is updated past the characters we use.  The value of the
 505    escape sequence is returned.
 506
 507    A negative value means the sequence \ newline was seen,
 508    which is supposed to be equivalent to nothing at all.
 509
 510    If \ is followed by a null character, we return a negative
 511    value and leave the string pointer pointing at the null character.
 512
 513    If \ is followed by 000, we return 0 and leave the string pointer
 514    after the zeros.  A value of 0 does not mean end of string.  */
 515
 516 HOST_WIDEST_INT
 517 cpp_parse_escape (pfile, string_ptr, result_mask)
 518      cpp_reader *pfile;
 519      char **string_ptr;
 520      HOST_WIDEST_INT result_mask;
 521 {
 522   register int c = *(*string_ptr)++;
 523   switch (c)
 524     {
 525     case 'a':
 526       return TARGET_BELL;
 527     case 'b':
 528       return TARGET_BS;
 529     case 'e':
 530     case 'E':
 531       if (CPP_OPTIONS (pfile)->pedantic)
 532         cpp_pedwarn (pfile, "non-ANSI-standard escape sequence, `\\%c'", c);
 533       return 033;
 534     case 'f':
 535       return TARGET_FF;
 536     case 'n':
 537       return TARGET_NEWLINE;
 538     case 'r':
 539       return TARGET_CR;
 540     case 't':
 541       return TARGET_TAB;
 542     case 'v':
 543       return TARGET_VT;
 544     case '\n':
 545       return -2;
 546     case 0:
 547       (*string_ptr)--;
 548       return 0;
 549
 550     case '0':
 551     case '1':
 552     case '2':
 553     case '3':
 554     case '4':
 555     case '5':
 556     case '6':
 557     case '7':
 558       {
 559         register HOST_WIDEST_INT i = c - '0';
 560         register int count = 0;
 561         while (++count < 3)
 562           {
 563             c = *(*string_ptr)++;
 564             if (c >= '0' && c <= '7')
 565               i = (i << 3) + c - '0';
 566             else
 567               {
 568                 (*string_ptr)--;
 569                 break;
 570               }
 571           }
 572         if (i != (i & result_mask))
 573           {
 574             i &= result_mask;
 575             cpp_pedwarn (pfile, "octal escape sequence out of range");
 576           }
 577         return i;
 578       }
 579     case 'x':
 580       {
 581         register unsigned HOST_WIDEST_INT i = 0, overflow = 0;
 582         register int digits_found = 0, digit;
 583         for (;;)
 584           {
 585             c = *(*string_ptr)++;
 586             if (c >= '0' && c <= '9')
 587               digit = c - '0';
 588             else if (c >= 'a' && c <= 'f')
 589               digit = c - 'a' + 10;
 590             else if (c >= 'A' && c <= 'F')
 591               digit = c - 'A' + 10;
 592             else
 593               {
 594                 (*string_ptr)--;
 595                 break;
 596               }
 597             overflow |= i ^ (i << 4 >> 4);
 598             i = (i << 4) + digit;
 599             digits_found = 1;
 600           }
 601         if (!digits_found)
 602           cpp_error (pfile, "\\x used with no following hex digits");
 603         if (overflow | (i != (i & result_mask)))
 604           {
 605             i &= result_mask;
 606             cpp_pedwarn (pfile, "hex escape sequence out of range");
 607           }
 608         return i;
 609       }
 610     default:
 611       return c;
 612     }
 613 }
 614
 615 static void
 616 integer_overflow (pfile)
 617      cpp_reader *pfile;
 618 {
 619   if (CPP_PEDANTIC (pfile))
 620     cpp_pedwarn (pfile, "integer overflow in preprocessor expression");
 621 }
 622
 623 static HOST_WIDEST_INT
 624 left_shift (pfile, a, unsignedp, b)
 625      cpp_reader *pfile;
 626      HOST_WIDEST_INT a;
 627      int unsignedp;
 628      unsigned HOST_WIDEST_INT b;
 629 {
 630   if (b >= HOST_BITS_PER_WIDEST_INT)
 631     {
 632       if (! unsignedp && a != 0)
 633         integer_overflow (pfile);
 634       return 0;
 635     }
 636   else if (unsignedp)
 637     return (unsigned HOST_WIDEST_INT) a << b;
 638   else
 639     {
 640       HOST_WIDEST_INT l = a << b;
 641       if (l >> b != a)
 642         integer_overflow (pfile);
 643       return l;
 644     }
 645 }
 646
 647 static HOST_WIDEST_INT
 648 right_shift (pfile, a, unsignedp, b)
 649      cpp_reader *pfile ATTRIBUTE_UNUSED;
 650      HOST_WIDEST_INT a;
 651      int unsignedp;
 652      unsigned HOST_WIDEST_INT b;
 653 {
 654   if (b >= HOST_BITS_PER_WIDEST_INT)
 655     return unsignedp ? 0 : a >> (HOST_BITS_PER_WIDEST_INT - 1);
 656   else if (unsignedp)
 657     return (unsigned HOST_WIDEST_INT) a >> b;
 658   else
 659     return a >> b;
 660 }
 661 \f
 662 /* These priorities are all even, so we can handle associatively.  */
 663 #define PAREN_INNER_PRIO 0
 664 #define COMMA_PRIO 4
 665 #define COND_PRIO (COMMA_PRIO+2)
 666 #define OROR_PRIO (COND_PRIO+2)
 667 #define ANDAND_PRIO (OROR_PRIO+2)
 668 #define OR_PRIO (ANDAND_PRIO+2)
 669 #define XOR_PRIO (OR_PRIO+2)
 670 #define AND_PRIO (XOR_PRIO+2)
 671 #define EQUAL_PRIO (AND_PRIO+2)
 672 #define LESS_PRIO (EQUAL_PRIO+2)
 673 #define SHIFT_PRIO (LESS_PRIO+2)
 674 #define PLUS_PRIO (SHIFT_PRIO+2)
 675 #define MUL_PRIO (PLUS_PRIO+2)
 676 #define UNARY_PRIO (MUL_PRIO+2)
 677 #define PAREN_OUTER_PRIO (UNARY_PRIO+2)
 678
 679 #define COMPARE(OP) \
 680   top->unsignedp = 0;\
 681   top->value = (unsigned1 || unsigned2) \
 682   ? (unsigned HOST_WIDEST_INT) v1 OP (unsigned HOST_WIDEST_INT) v2 : (v1 OP v2)
 683
 684 /* Parse and evaluate a C expression, reading from PFILE.
 685    Returns the value of the expression.  */
 686
 687 HOST_WIDEST_INT
 688 cpp_parse_expr (pfile)
 689      cpp_reader *pfile;
 690 {
 691   /* The implementation is an operator precedence parser,
 692      i.e. a bottom-up parser, using a stack for not-yet-reduced tokens.
 693
 694      The stack base is 'stack', and the current stack pointer is 'top'.
 695      There is a stack element for each operator (only),
 696      and the most recently pushed operator is 'top->op'.
 697      An operand (value) is stored in the 'value' field of the stack
 698      element of the operator that precedes it.
 699      In that case the 'flags' field has the HAVE_VALUE flag set.  */
 700
 701 #define INIT_STACK_SIZE 20
 702   struct operation init_stack[INIT_STACK_SIZE];
 703   struct operation *stack = init_stack;
 704   struct operation *limit = stack + INIT_STACK_SIZE;
 705   register struct operation *top = stack;
 706   int lprio, rprio;
 707   int skip_evaluation = 0;
 708
 709   top->rprio = 0;
 710   top->flags = 0;
 711   for (;;)
 712     {
 713       struct operation op;
 714       char flags = 0;
 715
 716       /* Read a token */
 717       op =  cpp_lex (pfile, skip_evaluation);
 718
 719       /* See if the token is an operand, in which case go to set_value.
 720          If the token is an operator, figure out its left and right
 721          priorities, and then goto maybe_reduce.  */
 722
 723       switch (op.op)
 724         {
 725         case NAME:
 726           abort ();
 727         case INT:  case CHAR:
 728           top->value = op.value;
 729           top->unsignedp = op.unsignedp;
 730           goto set_value;
 731         case 0:
 732           lprio = 0;  goto maybe_reduce;
 733         case '+':  case '-':
 734           /* Is this correct if unary ? FIXME */
 735           flags = RIGHT_OPERAND_REQUIRED;
 736           lprio = PLUS_PRIO;  rprio = lprio + 1;  goto maybe_reduce;
 737         case '!':  case '~':
 738           flags = RIGHT_OPERAND_REQUIRED;
 739           rprio = UNARY_PRIO;  lprio = rprio + 1;  goto maybe_reduce;
 740         case '*':  case '/':  case '%':
 741           lprio = MUL_PRIO;  goto binop;
 742         case '<':  case '>':  case LEQ:  case GEQ:
 743           lprio = LESS_PRIO;  goto binop;
 744         case EQUAL:  case NOTEQUAL:
 745           lprio = EQUAL_PRIO;  goto binop;
 746         case LSH:  case RSH:
 747           lprio = SHIFT_PRIO;  goto binop;
 748         case '&':  lprio = AND_PRIO;  goto binop;
 749         case '^':  lprio = XOR_PRIO;  goto binop;
 750         case '|':  lprio = OR_PRIO;  goto binop;
 751         case ANDAND:  lprio = ANDAND_PRIO;  goto binop;
 752         case OROR:  lprio = OROR_PRIO;  goto binop;
 753         case ',':
 754           lprio = COMMA_PRIO;  goto binop;
 755         case '(':
 756           lprio = PAREN_OUTER_PRIO;  rprio = PAREN_INNER_PRIO;
 757           goto maybe_reduce;
 758         case ')':
 759           lprio = PAREN_INNER_PRIO;  rprio = PAREN_OUTER_PRIO;
 760           goto maybe_reduce;
 761         case ':':
 762           lprio = COND_PRIO;  rprio = COND_PRIO;
 763           goto maybe_reduce;
 764         case '?':
 765           lprio = COND_PRIO + 1;  rprio = COND_PRIO;
 766           goto maybe_reduce;
 767         case ERROR:
 768           goto syntax_error;
 769         binop:
 770           flags = LEFT_OPERAND_REQUIRED|RIGHT_OPERAND_REQUIRED;
 771           rprio = lprio + 1;
 772           goto maybe_reduce;
 773         default:
 774           cpp_error (pfile, "invalid character in #if");
 775           goto syntax_error;
 776         }
 777
 778     set_value:
 779       /* Push a value onto the stack.  */
 780       if (top->flags & HAVE_VALUE)
 781         {
 782           cpp_error (pfile, "syntax error in #if");
 783           goto syntax_error;
 784         }
 785       top->flags |= HAVE_VALUE;
 786       continue;
 787
 788     maybe_reduce:
 789       /* Push an operator, and check if we can reduce now.  */
 790       while (top->rprio > lprio)
 791         {
 792           HOST_WIDEST_INT v1 = top[-1].value, v2 = top[0].value;
 793           int unsigned1 = top[-1].unsignedp, unsigned2 = top[0].unsignedp;
 794           top--;
 795           if ((top[1].flags & LEFT_OPERAND_REQUIRED)
 796               && ! (top[0].flags & HAVE_VALUE))
 797             {
 798               cpp_error (pfile, "syntax error - missing left operand");
 799               goto syntax_error;
 800             }
 801           if ((top[1].flags & RIGHT_OPERAND_REQUIRED)
 802               && ! (top[1].flags & HAVE_VALUE))
 803             {
 804               cpp_error (pfile, "syntax error - missing right operand");
 805               goto syntax_error;
 806             }
 807           /* top[0].value = (top[1].op)(v1, v2);*/
 808           switch (top[1].op)
 809             {
 810             case '+':
 811               if (!(top->flags & HAVE_VALUE))
 812                 { /* Unary '+' */
 813                   top->value = v2;
 814                   top->unsignedp = unsigned2;
 815                   top->flags |= HAVE_VALUE;
 816                 }
 817               else
 818                 {
 819                   top->value = v1 + v2;
 820                   top->unsignedp = unsigned1 || unsigned2;
 821                   if (! top->unsignedp && ! skip_evaluation
 822                       && ! possible_sum_sign (v1, v2, top->value))
 823                     integer_overflow (pfile);
 824                 }
 825               break;
 826             case '-':
 827               if (!(top->flags & HAVE_VALUE))
 828                 { /* Unary '-' */
 829                   top->value = - v2;
 830                   if (!skip_evaluation && (top->value & v2) < 0 && !unsigned2)
 831                     integer_overflow (pfile);
 832                   top->unsignedp = unsigned2;
 833                   top->flags |= HAVE_VALUE;
 834                 }
 835               else
 836                 { /* Binary '-' */
 837                   top->value = v1 - v2;
 838                   top->unsignedp = unsigned1 || unsigned2;
 839                   if (! top->unsignedp && ! skip_evaluation
 840                       && ! possible_sum_sign (top->value, v2, v1))
 841                     integer_overflow (pfile);
 842                 }
 843               break;
 844             case '*':
 845               top->unsignedp = unsigned1 || unsigned2;
 846               if (top->unsignedp)
 847                 top->value = (unsigned HOST_WIDEST_INT) v1 * v2;
 848               else if (!skip_evaluation)
 849                 {
 850                   top->value = v1 * v2;
 851                   if (v1
 852                       && (top->value / v1 != v2
 853                           || (top->value & v1 & v2) < 0))
 854                     integer_overflow (pfile);
 855                 }
 856               break;
 857             case '/':
 858               if (skip_evaluation)
 859                 break;
 860               if (v2 == 0)
 861                 {
 862                   cpp_error (pfile, "division by zero in #if");
 863                   v2 = 1;
 864                 }
 865               top->unsignedp = unsigned1 || unsigned2;
 866               if (top->unsignedp)
 867                 top->value = (unsigned HOST_WIDEST_INT) v1 / v2;
 868               else
 869                 {
 870                   top->value = v1 / v2;
 871                   if ((top->value & v1 & v2) < 0)
 872                     integer_overflow (pfile);
 873                 }
 874               break;
 875             case '%':
 876               if (skip_evaluation)
 877                 break;
 878               if (v2 == 0)
 879                 {
 880                   cpp_error (pfile, "division by zero in #if");
 881                   v2 = 1;
 882                 }
 883               top->unsignedp = unsigned1 || unsigned2;
 884               if (top->unsignedp)
 885                 top->value = (unsigned HOST_WIDEST_INT) v1 % v2;
 886               else
 887                 top->value = v1 % v2;
 888               break;
 889             case '!':
 890               if (top->flags & HAVE_VALUE)
 891                 {
 892                   cpp_error (pfile, "syntax error");
 893                   goto syntax_error;
 894                 }
 895               top->value = ! v2;
 896               top->unsignedp = 0;
 897               top->flags |= HAVE_VALUE;
 898               break;
 899             case '~':
 900               if (top->flags & HAVE_VALUE)
 901                 {
 902                   cpp_error (pfile, "syntax error");
 903                   goto syntax_error;
 904                 }
 905               top->value = ~ v2;
 906               top->unsignedp = unsigned2;
 907               top->flags |= HAVE_VALUE;
 908               break;
 909             case '<':  COMPARE(<);  break;
 910             case '>':  COMPARE(>);  break;
 911             case LEQ:  COMPARE(<=); break;
 912             case GEQ:  COMPARE(>=); break;
 913             case EQUAL:
 914               top->value = (v1 == v2);
 915               top->unsignedp = 0;
 916               break;
 917             case NOTEQUAL:
 918               top->value = (v1 != v2);
 919               top->unsignedp = 0;
 920               break;
 921             case LSH:
 922               if (skip_evaluation)
 923                 break;
 924               top->unsignedp = unsigned1;
 925               if (v2 < 0 && ! unsigned2)
 926                 top->value = right_shift (pfile, v1, unsigned1, -v2);
 927               else
 928                 top->value = left_shift (pfile, v1, unsigned1, v2);
 929               break;
 930             case RSH:
 931               if (skip_evaluation)
 932                 break;
 933               top->unsignedp = unsigned1;
 934               if (v2 < 0 && ! unsigned2)
 935                 top->value = left_shift (pfile, v1, unsigned1, -v2);
 936               else
 937                 top->value = right_shift (pfile, v1, unsigned1, v2);
 938               break;
 939 #define LOGICAL(OP) \
 940               top->value = v1 OP v2;\
 941               top->unsignedp = unsigned1 || unsigned2;
 942             case '&':  LOGICAL(&); break;
 943             case '^':  LOGICAL(^);  break;
 944             case '|':  LOGICAL(|);  break;
 945             case ANDAND:
 946               top->value = v1 && v2;  top->unsignedp = 0;
 947               if (!v1) skip_evaluation--;
 948               break;
 949             case OROR:
 950               top->value = v1 || v2;  top->unsignedp = 0;
 951               if (v1) skip_evaluation--;
 952               break;
 953             case ',':
 954               if (CPP_PEDANTIC (pfile))
 955                 cpp_pedwarn (pfile, "comma operator in operand of `#if'");
 956               top->value = v2;
 957               top->unsignedp = unsigned2;
 958               break;
 959             case '(':  case '?':
 960               cpp_error (pfile, "syntax error in #if");
 961               goto syntax_error;
 962             case ':':
 963               if (top[0].op != '?')
 964                 {
 965                   cpp_error (pfile,
 966                              "syntax error ':' without preceding '?'");
 967                   goto syntax_error;
 968                 }
 969               else if (! (top[1].flags & HAVE_VALUE)
 970                        || !(top[-1].flags & HAVE_VALUE)
 971                        || !(top[0].flags & HAVE_VALUE))
 972                 {
 973                   cpp_error (pfile, "bad syntax for ?: operator");
 974                   goto syntax_error;
 975                 }
 976               else
 977                 {
 978                   top--;
 979                   if (top->value) skip_evaluation--;
 980                   top->value = top->value ? v1 : v2;
 981                   top->unsignedp = unsigned1 || unsigned2;
 982                 }
 983               break;
 984             case ')':
 985               if ((top[1].flags & HAVE_VALUE)
 986                   || ! (top[0].flags & HAVE_VALUE)
 987                   || top[0].op != '('
 988                   || (top[-1].flags & HAVE_VALUE))
 989                 {
 990                   cpp_error (pfile, "mismatched parentheses in #if");
 991                   goto syntax_error;
 992                 }
 993               else
 994                 {
 995                   top--;
 996                   top->value = v1;
 997                   top->unsignedp = unsigned1;
 998                   top->flags |= HAVE_VALUE;
 999                 }
1000               break;
1001             default:
1002               cpp_error (pfile,
1003                          (top[1].op >= ' ' && top[1].op <= '~'
1004                           ? "unimplemented operator '%c'\n"
1005                           : "unimplemented operator '\\%03o'\n"),
1006                          top[1].op);
1007             }
1008         }
1009       if (op.op == 0)
1010         {
1011           if (top != stack)
1012             cpp_error (pfile, "internal error in #if expression");
1013           if (stack != init_stack)
1014             free (stack);
1015           return top->value;
1016         }
1017       top++;
1018
1019       /* Check for and handle stack overflow.  */
1020       if (top == limit)
1021         {
1022           struct operation *new_stack;
1023           int old_size = (char *) limit - (char *) stack;
1024           int new_size = 2 * old_size;
1025           if (stack != init_stack)
1026             new_stack = (struct operation *) xrealloc (stack, new_size);
1027           else
1028             {
1029               new_stack = (struct operation *) xmalloc (new_size);
1030               bcopy ((char *) stack, (char *) new_stack, old_size);
1031             }
1032           stack = new_stack;
1033           top = (struct operation *) ((char *) new_stack + old_size);
1034           limit = (struct operation *) ((char *) new_stack + new_size);
1035         }
1036
1037       top->flags = flags;
1038       top->rprio = rprio;
1039       top->op = op.op;
1040       if ((op.op == OROR && top[-1].value)
1041           || (op.op == ANDAND && !top[-1].value)
1042           || (op.op == '?' && !top[-1].value))
1043         {
1044           skip_evaluation++;
1045         }
1046       else if (op.op == ':')
1047         {
1048           if (top[-2].value) /* Was condition true? */
1049             skip_evaluation++;
1050           else
1051             skip_evaluation--;
1052         }
1053     }
1054  syntax_error:
1055   if (stack != init_stack)
1056     free (stack);
1057   skip_rest_of_line (pfile);
1058   return 0;
1059 }