gcc/cppexp.c

/* Parse C expressions for CCCP.
   Copyright (C) 1987, 1992, 1994, 1995, 1997, 1998 Free Software Foundation.

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.

 In other words, you are welcome to use, share and improve this program.
 You are forbidden to forbid anyone else to use, share and improve
 what you give them.   Help stamp out software-hoarding!

Written by Per Bothner 1994.  */

/* Parse a C expression from text in a string  */
   
#include "config.h"
#include "cpplib.h"
#include "gansidecl.h"

extern char *xmalloc PARAMS ((unsigned));
extern char *xrealloc PARAMS ((void *, unsigned));

#ifdef MULTIBYTE_CHARS
#include <stdlib.h>
#include <locale.h>
#endif

#if HAVE_LIMITS_H
# include <limits.h>
#endif

#include <stdio.h>

/* This is used for communicating lists of keywords with cccp.c.  */
struct arglist {
  struct arglist *next;
  U_CHAR *name;
  int length;
  int argno;
};

/* Define a generic NULL if one hasn't already been defined.  */

#ifndef NULL
#define NULL 0
#endif

#ifndef GENERIC_PTR
#if defined (USE_PROTOTYPES) ? USE_PROTOTYPES : defined (__STDC__)
#define GENERIC_PTR void *
#else
#define GENERIC_PTR char *
#endif
#endif

#ifndef NULL_PTR
#define NULL_PTR ((GENERIC_PTR) 0)
#endif

extern char *xmalloc ();

#ifndef CHAR_TYPE_SIZE
#define CHAR_TYPE_SIZE BITS_PER_UNIT
#endif

#ifndef INT_TYPE_SIZE
#define INT_TYPE_SIZE BITS_PER_WORD
#endif

#ifndef LONG_TYPE_SIZE
#define LONG_TYPE_SIZE BITS_PER_WORD
#endif

#ifndef WCHAR_TYPE_SIZE
#define WCHAR_TYPE_SIZE INT_TYPE_SIZE
#endif

#ifndef MAX_CHAR_TYPE_SIZE
#define MAX_CHAR_TYPE_SIZE CHAR_TYPE_SIZE
#endif

#ifndef MAX_INT_TYPE_SIZE
#define MAX_INT_TYPE_SIZE INT_TYPE_SIZE
#endif

#ifndef MAX_LONG_TYPE_SIZE
#define MAX_LONG_TYPE_SIZE LONG_TYPE_SIZE
#endif

#ifndef MAX_WCHAR_TYPE_SIZE
#define MAX_WCHAR_TYPE_SIZE WCHAR_TYPE_SIZE
#endif

/* Yield nonzero if adding two numbers with A's and B's signs can yield a
   number with SUM's sign, where A, B, and SUM are all C integers.  */
#define possible_sum_sign(a, b, sum) ((((a) ^ (b)) | ~ ((a) ^ (sum))) < 0)

static void integer_overflow ();
static long left_shift ();
static long right_shift ();

#define ERROR 299
#define OROR 300
#define ANDAND 301
#define EQUAL 302
#define NOTEQUAL 303
#define LEQ 304
#define GEQ 305
#define LSH 306
#define RSH 307
#define NAME 308
#define INT 309
#define CHAR 310

#define LEFT_OPERAND_REQUIRED 1
#define RIGHT_OPERAND_REQUIRED 2
#define HAVE_VALUE 4
/* SKIP_OPERAND is set for '&&' '||' '?' and ':' when the
   following operand should be short-circuited instead of evaluated.  */
#define SKIP_OPERAND 8
/*#define UNSIGNEDP 16*/

/* Find the largest host integer type and set its size and type.
   Watch out: on some crazy hosts `long' is shorter than `int'.  */

#ifndef HOST_WIDE_INT
# if HAVE_INTTYPES_H
#  include <inttypes.h>
#  define HOST_WIDE_INT intmax_t
# else
#  if (HOST_BITS_PER_LONG <= HOST_BITS_PER_INT \
       && HOST_BITS_PER_LONGLONG <= HOST_BITS_PER_INT)
#   define HOST_WIDE_INT int
#  else
#  if (HOST_BITS_PER_LONGLONG <= HOST_BITS_PER_LONG \
       || ! (defined LONG_LONG_MAX || defined LLONG_MAX))
#   define HOST_WIDE_INT long
#  else
#   define HOST_WIDE_INT long long
#  endif
#  endif
# endif
#endif

#ifndef CHAR_BIT
#define CHAR_BIT 8
#endif

#ifndef HOST_BITS_PER_WIDE_INT
#define HOST_BITS_PER_WIDE_INT (CHAR_BIT * sizeof (HOST_WIDE_INT))
#endif

struct operation {
    short op;
    char rprio; /* Priority of op (relative to it right operand).  */
    char flags;
    char unsignedp;    /* true if value should be treated as unsigned */
    HOST_WIDE_INT value;        /* The value logically "right" of op.  */
};

/* Take care of parsing a number (anything that starts with a digit).
   LEN is the number of characters in it.  */

/* maybe needs to actually deal with floating point numbers */

struct operation
parse_number (pfile, start, olen)
     cpp_reader *pfile;
     char *start;
     int olen;
{
  struct operation op;
  register char *p = start;
  register int c;
  register unsigned long n = 0, nd, ULONG_MAX_over_base;
  register int base = 10;
  register int len = olen;
  register int overflow = 0;
  register int digit, largest_digit = 0;
  int spec_long = 0;

  op.unsignedp = 0;

  for (c = 0; c < len; c++)
    if (p[c] == '.') {
      /* It's a float since it contains a point.  */
      cpp_error (pfile,
		 "floating point numbers not allowed in #if expressions");
      op.op = ERROR;
      return op;
    }

  if (len >= 3 && (!strncmp (p, "0x", 2) || !strncmp (p, "0X", 2))) {
    p += 2;
    base = 16;
    len -= 2;
  }
  else if (*p == '0')
    base = 8;

  /* Some buggy compilers (e.g. MPW C) seem to need both casts.  */
  ULONG_MAX_over_base = ((unsigned long) -1) / ((unsigned long) base);

  for (; len > 0; len--) {
    c = *p++;

    if (c >= '0' && c <= '9')
      digit = c - '0';
    else if (base == 16 && c >= 'a' && c <= 'f')
      digit = c - 'a' + 10;
    else if (base == 16 && c >= 'A' && c <= 'F')
      digit = c - 'A' + 10;
    else {
      /* `l' means long, and `u' means unsigned.  */
      while (1) {
	if (c == 'l' || c == 'L')
	  {
	    if (spec_long)
	      cpp_error (pfile, "two `l's in integer constant");
	    spec_long = 1;
	  }
	else if (c == 'u' || c == 'U')
	  {
	    if (op.unsignedp)
	      cpp_error (pfile, "two `u's in integer constant");
	    op.unsignedp = 1;
	  }
	else
	  break;

	if (--len == 0)
	  break;
	c = *p++;
      }
      /* Don't look for any more digits after the suffixes.  */
      break;
    }
    if (largest_digit < digit)
      largest_digit = digit;
    nd = n * base + digit;
    overflow |= ULONG_MAX_over_base < n | nd < n;
    n = nd;
  }

  if (len != 0)
    {
      cpp_error (pfile, "Invalid number in #if expression");
      op.op = ERROR;
      return op;
    }

  if (base <= largest_digit)
    cpp_pedwarn (pfile, "integer constant contains digits beyond the radix");

  if (overflow)
    cpp_pedwarn (pfile, "integer constant out of range");

  /* If too big to be signed, consider it unsigned.  */
  if ((long) n < 0 && ! op.unsignedp)
    {
      if (base == 10)
	cpp_warning (pfile, "integer constant is so large that it is unsigned");
      op.unsignedp = 1;
    }

  op.value = n;
  op.op = INT;
  return op;
}

struct token {
  char *operator;
  int token;
};

static struct token tokentab2[] = {
  {"&&", ANDAND},
  {"||", OROR},
  {"<<", LSH},
  {">>", RSH},
  {"==", EQUAL},
  {"!=", NOTEQUAL},
  {"<=", LEQ},
  {">=", GEQ},
  {"++", ERROR},
  {"--", ERROR},
  {NULL, ERROR}
};

/* Read one token.  */

struct operation
cpp_lex (pfile, skip_evaluation)
     cpp_reader *pfile;
     int skip_evaluation;
{
  register int c;
  register int namelen;
  register struct token *toktab;
  enum cpp_token token;
  struct operation op;
  U_CHAR *tok_start, *tok_end;
  int old_written;

 retry:

  old_written = CPP_WRITTEN (pfile);
  cpp_skip_hspace (pfile);
  c = CPP_BUF_PEEK (CPP_BUFFER (pfile));
  if (c == '#')
    return parse_number (pfile,
			 cpp_read_check_assertion (pfile) ? "1" : "0", 1);

  if (c == '\n')
    {
      op.op = 0;
      return op;
    }

  token = cpp_get_token (pfile);
  tok_start = pfile->token_buffer + old_written;
  tok_end = CPP_PWRITTEN (pfile);
  pfile->limit = tok_start;
  switch (token)
  {
    case CPP_EOF: /* Should not happen ...  */
    case CPP_VSPACE:
      op.op = 0;
      return op;
    case CPP_POP:
      if (CPP_BUFFER (pfile)->fname != NULL)
	{
	  op.op = 0;
	  return op;
	}
      cpp_pop_buffer (pfile);
      goto retry;
    case CPP_HSPACE:   case CPP_COMMENT: 
      goto retry;
    case CPP_NUMBER:
      return parse_number (pfile, tok_start, tok_end - tok_start);
    case CPP_STRING:
      cpp_error (pfile, "string constants not allowed in #if expressions");
      op.op = ERROR;
      return op;
    case CPP_CHAR:
      /* This code for reading a character constant
	 handles multicharacter constants and wide characters.
	 It is mostly copied from c-lex.c.  */
      {
        register int result = 0;
	register num_chars = 0;
	unsigned width = MAX_CHAR_TYPE_SIZE;
	int wide_flag = 0;
	int max_chars;
	U_CHAR *ptr = tok_start;
#ifdef MULTIBYTE_CHARS
	char token_buffer[MAX_LONG_TYPE_SIZE/MAX_CHAR_TYPE_SIZE + MB_CUR_MAX];
#else
	char token_buffer[MAX_LONG_TYPE_SIZE/MAX_CHAR_TYPE_SIZE + 1];
#endif

	if (*ptr == 'L')
	  {
	    ptr++;
	    wide_flag = 1;
	    width = MAX_WCHAR_TYPE_SIZE;
#ifdef MULTIBYTE_CHARS
	    max_chars = MB_CUR_MAX;
#else
	    max_chars = 1;
#endif
	  }
	else
	    max_chars = MAX_LONG_TYPE_SIZE / width;

	++ptr;
	while (ptr < tok_end && ((c = *ptr++) != '\''))
	  {
	    if (c == '\\')
	      {
		c = cpp_parse_escape (pfile, (char **) &ptr);
		if (width < HOST_BITS_PER_INT
		  && (unsigned) c >= (1 << width))
		    cpp_pedwarn (pfile,
				 "escape sequence out of range for character");
	      }

	    num_chars++;

	    /* Merge character into result; ignore excess chars.  */
	    if (num_chars < max_chars + 1)
	      {
	        if (width < HOST_BITS_PER_INT)
		  result = (result << width) | (c & ((1 << width) - 1));
		else
		  result = c;
		token_buffer[num_chars - 1] = c;
	      }
	  }

	token_buffer[num_chars] = 0;

	if (c != '\'')
	  cpp_error (pfile, "malformatted character constant");
	else if (num_chars == 0)
	  cpp_error (pfile, "empty character constant");
	else if (num_chars > max_chars)
	  {
	    num_chars = max_chars;
	    cpp_error (pfile, "character constant too long");
	  }
	else if (num_chars != 1 && ! CPP_TRADITIONAL (pfile))
	  cpp_warning (pfile, "multi-character character constant");

	/* If char type is signed, sign-extend the constant.  */
	if (! wide_flag)
	  {
	    int num_bits = num_chars * width;

	    if (cpp_lookup (pfile, (U_CHAR *)"__CHAR_UNSIGNED__",
			    sizeof ("__CHAR_UNSIGNED__")-1, -1)
		|| ((result >> (num_bits - 1)) & 1) == 0)
		op.value
		    = result & ((unsigned long) ~0 >> (HOST_BITS_PER_LONG - num_bits));
	    else
		op.value
		    = result | ~((unsigned long) ~0 >> (HOST_BITS_PER_LONG - num_bits));
	  }
	else
	  {
#ifdef MULTIBYTE_CHARS
	    /* Set the initial shift state and convert the next sequence.  */
	      result = 0;
	      /* In all locales L'\0' is zero and mbtowc will return zero,
		 so don't use it.  */
	      if (num_chars > 1
		  || (num_chars == 1 && token_buffer[0] != '\0'))
	        {
		  wchar_t wc;
		  (void) mbtowc (NULL_PTR, NULL_PTR, 0);
		  if (mbtowc (& wc, token_buffer, num_chars) == num_chars)
		    result = wc;
		  else
		    cpp_pedwarn (pfile,"Ignoring invalid multibyte character");
	        }
#endif
	      op.value = result;
	    }
        }

      /* This is always a signed type.  */
      op.unsignedp = 0;
      op.op = CHAR;
    
      return op;

    case CPP_NAME:
      if (CPP_WARN_UNDEF (pfile) && !skip_evaluation)
	cpp_warning (pfile, "`%.*s' is not defined",
		     (int) (tok_end - tok_start), tok_start);
      return parse_number (pfile, "0", 0);

    case CPP_OTHER:
      /* See if it is a special token of length 2.  */
      if (tok_start + 2 == tok_end)
        {
	  for (toktab = tokentab2; toktab->operator != NULL; toktab++)
	    if (tok_start[0] == toktab->operator[0]
		&& tok_start[1] == toktab->operator[1])
		break;
	  if (toktab->token == ERROR)
	    {
	      char *buf = (char *) alloca (40);
	      sprintf (buf, "`%s' not allowed in operand of `#if'", tok_start);
	      cpp_error (pfile, buf);
	    }
	  op.op = toktab->token; 
	  return op;
	}
      /* fall through */
    default:
      op.op = *tok_start;
      return op;
  }
}


/* Parse a C escape sequence.  STRING_PTR points to a variable
   containing a pointer to the string to parse.  That pointer
   is updated past the characters we use.  The value of the
   escape sequence is returned.

   A negative value means the sequence \ newline was seen,
   which is supposed to be equivalent to nothing at all.

   If \ is followed by a null character, we return a negative
   value and leave the string pointer pointing at the null character.

   If \ is followed by 000, we return 0 and leave the string pointer
   after the zeros.  A value of 0 does not mean end of string.  */

int
cpp_parse_escape (pfile, string_ptr)
     cpp_reader *pfile;
     char **string_ptr;
{
  register int c = *(*string_ptr)++;
  switch (c)
    {
    case 'a':
      return TARGET_BELL;
    case 'b':
      return TARGET_BS;
    case 'e':
    case 'E':
      if (CPP_PEDANTIC (pfile))
	cpp_pedwarn (pfile, "non-ANSI-standard escape sequence, `\\%c'", c);
      return 033;
    case 'f':
      return TARGET_FF;
    case 'n':
      return TARGET_NEWLINE;
    case 'r':
      return TARGET_CR;
    case 't':
      return TARGET_TAB;
    case 'v':
      return TARGET_VT;
    case '\n':
      return -2;
    case 0:
      (*string_ptr)--;
      return 0;
      
    case '0':
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
      {
	register int i = c - '0';
	register int count = 0;
	while (++count < 3)
	  {
	    c = *(*string_ptr)++;
	    if (c >= '0' && c <= '7')
	      i = (i << 3) + c - '0';
	    else
	      {
		(*string_ptr)--;
		break;
	      }
	  }
	if ((i & ~((1 << MAX_CHAR_TYPE_SIZE) - 1)) != 0)
	  {
	    i &= (1 << MAX_CHAR_TYPE_SIZE) - 1;
	    cpp_pedwarn (pfile,
			  "octal character constant does not fit in a byte");
	  }
	return i;
      }
    case 'x':
      {
	register unsigned i = 0, overflow = 0, digits_found = 0, digit;
	for (;;)
	  {
	    c = *(*string_ptr)++;
	    if (c >= '0' && c <= '9')
	      digit = c - '0';
	    else if (c >= 'a' && c <= 'f')
	      digit = c - 'a' + 10;
	    else if (c >= 'A' && c <= 'F')
	      digit = c - 'A' + 10;
	    else
	      {
		(*string_ptr)--;
		break;
	      }
	    overflow |= i ^ (i << 4 >> 4);
	    i = (i << 4) + digit;
	    digits_found = 1;
	  }
	if (!digits_found)
	  cpp_error (pfile, "\\x used with no following hex digits");
	if (overflow | (i & ~((1 << BITS_PER_UNIT) - 1)))
	  {
	    i &= (1 << BITS_PER_UNIT) - 1;
	    cpp_pedwarn (pfile,
			 "hex character constant does not fit in a byte");
	  }
	return i;
      }
    default:
      return c;
    }
}

static void
integer_overflow (pfile)
     cpp_reader *pfile;
{
  if (CPP_PEDANTIC (pfile))
    cpp_pedwarn (pfile, "integer overflow in preprocessor expression");
}

static long
left_shift (pfile, a, unsignedp, b)
     cpp_reader *pfile;
     long a;
     int unsignedp;
     unsigned long b;
{
  if (b >= HOST_BITS_PER_LONG)
    {
      if (! unsignedp && a != 0)
	integer_overflow (pfile);
      return 0;
    }
  else if (unsignedp)
    return (unsigned long) a << b;
  else
    {
      long l = a << b;
      if (l >> b != a)
	integer_overflow (pfile);
      return l;
    }
}

static long
right_shift (pfile, a, unsignedp, b)
     cpp_reader *pfile;
     long a;
     int unsignedp;
     unsigned long b;
{
  if (b >= HOST_BITS_PER_LONG)
    return unsignedp ? 0 : a >> (HOST_BITS_PER_LONG - 1);
  else if (unsignedp)
    return (unsigned long) a >> b;
  else
    return a >> b;
}

/* These priorities are all even, so we can handle associatively.  */
#define PAREN_INNER_PRIO 0
#define COMMA_PRIO 4
#define COND_PRIO (COMMA_PRIO+2)
#define OROR_PRIO (COND_PRIO+2)
#define ANDAND_PRIO (OROR_PRIO+2)
#define OR_PRIO (ANDAND_PRIO+2)
#define XOR_PRIO (OR_PRIO+2)
#define AND_PRIO (XOR_PRIO+2)
#define EQUAL_PRIO (AND_PRIO+2)
#define LESS_PRIO (EQUAL_PRIO+2)
#define SHIFT_PRIO (LESS_PRIO+2)
#define PLUS_PRIO (SHIFT_PRIO+2)
#define MUL_PRIO (PLUS_PRIO+2)
#define UNARY_PRIO (MUL_PRIO+2)
#define PAREN_OUTER_PRIO (UNARY_PRIO+2)

#define COMPARE(OP) \
  top->unsignedp = 0;\
  top->value = (unsigned1 || unsigned2) ? (unsigned long) v1 OP v2 : (v1 OP v2)

/* Parse and evaluate a C expression, reading from PFILE.
   Returns the value of the expression.  */

HOST_WIDE_INT
cpp_parse_expr (pfile)
     cpp_reader *pfile;
{
  /* The implementation is an operator precedence parser,
     i.e. a bottom-up parser, using a stack for not-yet-reduced tokens.

     The stack base is 'stack', and the current stack pointer is 'top'.
     There is a stack element for each operator (only),
     and the most recently pushed operator is 'top->op'.
     An operand (value) is stored in the 'value' field of the stack
     element of the operator that precedes it.
     In that case the 'flags' field has the HAVE_VALUE flag set.  */

#define INIT_STACK_SIZE 20
  struct operation init_stack[INIT_STACK_SIZE];
  struct operation *stack = init_stack;
  struct operation *limit = stack + INIT_STACK_SIZE;
  register struct operation *top = stack;
  int lprio, rprio;
  int skip_evaluation = 0;

  top->rprio = 0;
  top->flags = 0;
  for (;;)
    {
      struct operation op;
      char flags = 0;

      /* Read a token */
      op =  cpp_lex (pfile, skip_evaluation);

      /* See if the token is an operand, in which case go to set_value.
	 If the token is an operator, figure out its left and right
	 priorities, and then goto maybe_reduce.  */

      switch (op.op)
	{
	case NAME:
	  abort ();
	case INT:  case CHAR:
	  top->value = op.value;
	  top->unsignedp = op.unsignedp;
	  goto set_value;
	case 0:
	  lprio = 0;  goto maybe_reduce;
	case '+':  case '-':
	  /* Is this correct if unary ? FIXME */
	  flags = RIGHT_OPERAND_REQUIRED;
	  lprio = PLUS_PRIO;  rprio = lprio + 1;  goto maybe_reduce;
	case '!':  case '~':
	  flags = RIGHT_OPERAND_REQUIRED;
	  rprio = UNARY_PRIO;  lprio = rprio + 1;  goto maybe_reduce;
	case '*':  case '/':  case '%':
	  lprio = MUL_PRIO;  goto binop;
	case '<':  case '>':  case LEQ:  case GEQ:
	  lprio = LESS_PRIO;  goto binop;
	case EQUAL:  case NOTEQUAL:
	  lprio = EQUAL_PRIO;  goto binop;
	case LSH:  case RSH:
	  lprio = SHIFT_PRIO;  goto binop;
	case '&':  lprio = AND_PRIO;  goto binop;
	case '^':  lprio = XOR_PRIO;  goto binop;
	case '|':  lprio = OR_PRIO;  goto binop;
	case ANDAND:  lprio = ANDAND_PRIO;  goto binop;
	case OROR:  lprio = OROR_PRIO;  goto binop;
	case ',':
	  lprio = COMMA_PRIO;  goto binop;
	case '(':
	  lprio = PAREN_OUTER_PRIO;  rprio = PAREN_INNER_PRIO;
	  goto maybe_reduce;
	case ')':
	  lprio = PAREN_INNER_PRIO;  rprio = PAREN_OUTER_PRIO;
	  goto maybe_reduce;
        case ':':
	  lprio = COND_PRIO;  rprio = COND_PRIO;
	  goto maybe_reduce;
        case '?':
	  lprio = COND_PRIO + 1;  rprio = COND_PRIO;
	  goto maybe_reduce;
	binop:
	  flags = LEFT_OPERAND_REQUIRED|RIGHT_OPERAND_REQUIRED;
	  rprio = lprio + 1;
	  goto maybe_reduce;
	default:
	  cpp_error (pfile, "invalid character in #if");
	  goto syntax_error;
	}

    set_value:
      /* Push a value onto the stack.  */
      if (top->flags & HAVE_VALUE)
	{
	  cpp_error (pfile, "syntax error in #if");
	  goto syntax_error;
	}
      top->flags |= HAVE_VALUE;
      continue;

    maybe_reduce:
      /* Push an operator, and check if we can reduce now.  */
      while (top->rprio > lprio)
	{
	  long v1 = top[-1].value, v2 = top[0].value;
	  int unsigned1 = top[-1].unsignedp, unsigned2 = top[0].unsignedp;
	  top--;
	  if ((top[1].flags & LEFT_OPERAND_REQUIRED)
	      && ! (top[0].flags & HAVE_VALUE))
	    {
	      cpp_error (pfile, "syntax error - missing left operand");
	      goto syntax_error;
	    }
	  if ((top[1].flags & RIGHT_OPERAND_REQUIRED)
	      && ! (top[1].flags & HAVE_VALUE))
	    {
	      cpp_error (pfile, "syntax error - missing right operand");
	      goto syntax_error;
	    }
	  /* top[0].value = (top[1].op)(v1, v2);*/
	  switch (top[1].op)
	    {
	    case '+':
	      if (!(top->flags & HAVE_VALUE))
		{ /* Unary '+' */
		  top->value = v2;
		  top->unsignedp = unsigned2;
		  top->flags |= HAVE_VALUE;
		}
	      else
		{
		  top->value = v1 + v2;
		  top->unsignedp = unsigned1 || unsigned2;
		  if (! top->unsignedp && ! skip_evaluation
		      && ! possible_sum_sign (v1, v2, top->value))
		    integer_overflow (pfile);
		}
	      break;
	    case '-':
	      if (!(top->flags & HAVE_VALUE))
		{ /* Unary '-' */
		  top->value = - v2;
		  if (!skip_evaluation && (top->value & v2) < 0 && !unsigned2)
		    integer_overflow (pfile);
		  top->unsignedp = unsigned2;
		  top->flags |= HAVE_VALUE;
		}
	      else
		{ /* Binary '-' */
		  top->value = v1 - v2;
		  top->unsignedp = unsigned1 || unsigned2;
		  if (! top->unsignedp && ! skip_evaluation
		      && ! possible_sum_sign (top->value, v2, v1))
		    integer_overflow (pfile);
		}
	      break;
	    case '*':
	      top->unsignedp = unsigned1 || unsigned2;
	      if (top->unsignedp)
		top->value = (unsigned long) v1 * v2;
	      else if (!skip_evaluation)
		{
		  top->value = v1 * v2;
		  if (v1
		      && (top->value / v1 != v2
			  || (top->value & v1 & v2) < 0))
		    integer_overflow (pfile);
		}
	      break;
	    case '/':
	      if (skip_evaluation)
		break;
	      if (v2 == 0)
		{
		  cpp_error (pfile, "division by zero in #if");
		  v2 = 1;
		}
	      top->unsignedp = unsigned1 || unsigned2;
	      if (top->unsignedp)
		top->value = (unsigned long) v1 / v2;
	      else
		{
		  top->value = v1 / v2;
		  if ((top->value & v1 & v2) < 0)
		    integer_overflow (pfile);
		}
	      break;
	    case '%':
	      if (skip_evaluation)
		break;
	      if (v2 == 0)
		{
		  cpp_error (pfile, "division by zero in #if");
		  v2 = 1;
		}
	      top->unsignedp = unsigned1 || unsigned2;
	      if (top->unsignedp)
		top->value = (unsigned long) v1 % v2;
	      else
		top->value = v1 % v2;
	      break;
	    case '!':
	      if (top->flags & HAVE_VALUE)
		{
		  cpp_error (pfile, "syntax error");
		  goto syntax_error;
		}
	      top->value = ! v2;
	      top->unsignedp = 0;
	      top->flags |= HAVE_VALUE;
	      break;
	    case '~':
	      if (top->flags & HAVE_VALUE)
		{
		  cpp_error (pfile, "syntax error");
		  goto syntax_error;
		}
	      top->value = ~ v2;
	      top->unsignedp = unsigned2;
	      top->flags |= HAVE_VALUE;
	      break;
	    case '<':  COMPARE(<);  break;
	    case '>':  COMPARE(>);  break;
	    case LEQ:  COMPARE(<=); break;
	    case GEQ:  COMPARE(>=); break;
	    case EQUAL:
	      top->value = (v1 == v2);
	      top->unsignedp = 0;
	      break;
	    case NOTEQUAL:
	      top->value = (v1 != v2);
	      top->unsignedp = 0;
	      break;
	    case LSH:
	      if (skip_evaluation)
		break;
	      top->unsignedp = unsigned1;
	      if (v2 < 0 && ! unsigned2)
		top->value = right_shift (pfile, v1, unsigned1, -v2);
	      else
		top->value = left_shift (pfile, v1, unsigned1, v2);
	      break;
	    case RSH:
	      if (skip_evaluation)
		break;
	      top->unsignedp = unsigned1;
	      if (v2 < 0 && ! unsigned2)
		top->value = left_shift (pfile, v1, unsigned1, -v2);
	      else
		top->value = right_shift (pfile, v1, unsigned1, v2);
	      break;
#define LOGICAL(OP) \
	      top->value = v1 OP v2;\
	      top->unsignedp = unsigned1 || unsigned2;
	    case '&':  LOGICAL(&); break;
	    case '^':  LOGICAL(^);  break;
	    case '|':  LOGICAL(|);  break;
	    case ANDAND:
	      top->value = v1 && v2;  top->unsignedp = 0;
	      if (!v1) skip_evaluation--;
	      break;
	    case OROR:
	      top->value = v1 || v2;  top->unsignedp = 0;
	      if (v1) skip_evaluation--;
	      break;
	    case ',':
	      if (CPP_PEDANTIC (pfile))
		cpp_pedwarn (pfile, "comma operator in operand of `#if'");
	      top->value = v2;
	      top->unsignedp = unsigned2;
	      break;
	    case '(':  case '?':
	      cpp_error (pfile, "syntax error in #if");
	      goto syntax_error;
	    case ':':
	      if (top[0].op != '?')
		{
		  cpp_error (pfile,
			     "syntax error ':' without preceding '?'");
		  goto syntax_error;
		}
	      else if (! (top[1].flags & HAVE_VALUE)
		       || !(top[-1].flags & HAVE_VALUE)
		       || !(top[0].flags & HAVE_VALUE))
		{
		  cpp_error (pfile, "bad syntax for ?: operator");
		  goto syntax_error;
		}
	      else
		{
		  top--;
		  if (top->value) skip_evaluation--;
		  top->value = top->value ? v1 : v2;
		  top->unsignedp = unsigned1 || unsigned2;
		}
	      break;
	    case ')':
	      if ((top[1].flags & HAVE_VALUE)
		  || ! (top[0].flags & HAVE_VALUE)
		  || top[0].op != '('
		  || (top[-1].flags & HAVE_VALUE))
		{
		  cpp_error (pfile, "mismatched parentheses in #if");
		  goto syntax_error;
		}
	      else
		{
		  top--;
		  top->value = v1;
		  top->unsignedp = unsigned1;
		  top->flags |= HAVE_VALUE;
		}
	      break;
	    default:
	      fprintf (stderr,
		       top[1].op >= ' ' && top[1].op <= '~'
		       ? "unimplemented operator '%c'\n"
		       : "unimplemented operator '\\%03o'\n",
		       top[1].op);
	    }
	}
      if (op.op == 0)
	{
	  if (top != stack)
	    cpp_error (pfile, "internal error in #if expression");
	  if (stack != init_stack)
	    free (stack);
	  return top->value;
	}
      top++;
      
      /* Check for and handle stack overflow.  */
      if (top == limit)
	{
	  struct operation *new_stack;
	  int old_size = (char *) limit - (char *) stack;
	  int new_size = 2 * old_size;
	  if (stack != init_stack)
	    new_stack = (struct operation *) xrealloc (stack, new_size);
	  else
	    {
	      new_stack = (struct operation *) xmalloc (new_size);
	      bcopy ((char *) stack, (char *) new_stack, old_size);
	    }
	  stack = new_stack;
	  top = (struct operation *) ((char *) new_stack + old_size);
	  limit = (struct operation *) ((char *) new_stack + new_size);
	}
      
      top->flags = flags;
      top->rprio = rprio;
      top->op = op.op;
      if ((op.op == OROR && top[-1].value)
	  || (op.op == ANDAND && !top[-1].value)
	  || (op.op == '?' && !top[-1].value))
	{
	  skip_evaluation++;
	}
      else if (op.op == ':')
	{
	  if (top[-2].value) /* Was condition true? */
	    skip_evaluation++;
	  else
	    skip_evaluation--;
	}
    }
 syntax_error:
  if (stack != init_stack)
    free (stack);
  skip_rest_of_line (pfile);
  return 0;
}