cppexp.c

gcc库的原代码,对编程有很大帮助.

    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_warning (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_warning (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;

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

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

      /* 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:
	  top->value = 0, top->unsignedp = 0;
	  goto set_value;
	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
		      && ! possible_sum_sign (v1, v2, top->value))
		    integer_overflow (pfile);
		}
	      break;
	    case '-':
	      if (!(top->flags & HAVE_VALUE))
		{ /* Unary '-' */
		  top->value = - v2;
		  if ((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
		      && ! 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
		{
		  top->value = v1 * v2;
		  if (v1
		      && (top->value / v1 != v2
			  || (top->value & v1 & v2) < 0))
		    integer_overflow (pfile);
		}
	      break;
	    case '/':
	      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 (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:
	      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:
	      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;  break;
	    case OROR:
	      top->value = v1 || v2;  top->unsignedp = 0;  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--;
		  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;
    }
 syntax_error:
  if (stack != init_stack)
    free (stack);
  skip_rest_of_line (pfile);
  return 0;
}