* expr.c (expr): Simplify foo-foo here.

[deliverable/binutils-gdb.git] / gas / expr.c

/* expr.c -operands, expressions-
   Copyright 1987, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   1999, 2000, 2001, 2002
   Free Software Foundation, Inc.

   This file is part of GAS, the GNU Assembler.

   GAS 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.

   GAS 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 GAS; see the file COPYING.  If not, write to the Free
   Software Foundation, 59 Temple Place - Suite 330, Boston, MA
   02111-1307, USA.  */

/* This is really a branch office of as-read.c. I split it out to clearly
   distinguish the world of expressions from the world of statements.
   (It also gives smaller files to re-compile.)
   Here, "operand"s are of expressions, not instructions.  */

#include <string.h>
#define min(a, b)       ((a) < (b) ? (a) : (b))

#include "as.h"
#include "safe-ctype.h"
#include "obstack.h"

static void floating_constant PARAMS ((expressionS * expressionP));
static valueT generic_bignum_to_int32 PARAMS ((void));
#ifdef BFD64
static valueT generic_bignum_to_int64 PARAMS ((void));
#endif
static void integer_constant PARAMS ((int radix, expressionS * expressionP));
static void mri_char_constant PARAMS ((expressionS *));
static void current_location PARAMS ((expressionS *));
static void clean_up_expression PARAMS ((expressionS * expressionP));
static segT operand PARAMS ((expressionS *));
static operatorT operator PARAMS ((int *));

extern const char EXP_CHARS[], FLT_CHARS[];

/* We keep a mapping of expression symbols to file positions, so that
   we can provide better error messages.  */

struct expr_symbol_line {
  struct expr_symbol_line *next;
  symbolS *sym;
  char *file;
  unsigned int line;
};

static struct expr_symbol_line *expr_symbol_lines;
\f
/* Build a dummy symbol to hold a complex expression.  This is how we
   build expressions up out of other expressions.  The symbol is put
   into the fake section expr_section.  */

symbolS *
make_expr_symbol (expressionP)
     expressionS *expressionP;
{
  expressionS zero;
  const char *fake;
  symbolS *symbolP;
  struct expr_symbol_line *n;

  if (expressionP->X_op == O_symbol
      && expressionP->X_add_number == 0)
    return expressionP->X_add_symbol;

  if (expressionP->X_op == O_big)
    {
      /* This won't work, because the actual value is stored in
         generic_floating_point_number or generic_bignum, and we are
         going to lose it if we haven't already.  */
      if (expressionP->X_add_number > 0)
        as_bad (_("bignum invalid"));
      else
        as_bad (_("floating point number invalid"));
      zero.X_op = O_constant;
      zero.X_add_number = 0;
      zero.X_unsigned = 0;
      clean_up_expression (&zero);
      expressionP = &zero;
    }

  fake = FAKE_LABEL_NAME;

  /* Putting constant symbols in absolute_section rather than
     expr_section is convenient for the old a.out code, for which
     S_GET_SEGMENT does not always retrieve the value put in by
     S_SET_SEGMENT.  */
  symbolP = symbol_create (fake,
                           (expressionP->X_op == O_constant
                            ? absolute_section
                            : expr_section),
                           0, &zero_address_frag);
  symbol_set_value_expression (symbolP, expressionP);

  if (expressionP->X_op == O_constant)
    resolve_symbol_value (symbolP);

  n = (struct expr_symbol_line *) xmalloc (sizeof *n);
  n->sym = symbolP;
  as_where (&n->file, &n->line);
  n->next = expr_symbol_lines;
  expr_symbol_lines = n;

  return symbolP;
}

/* Return the file and line number for an expr symbol.  Return
   non-zero if something was found, 0 if no information is known for
   the symbol.  */

int
expr_symbol_where (sym, pfile, pline)
     symbolS *sym;
     char **pfile;
     unsigned int *pline;
{
  register struct expr_symbol_line *l;

  for (l = expr_symbol_lines; l != NULL; l = l->next)
    {
      if (l->sym == sym)
        {
          *pfile = l->file;
          *pline = l->line;
          return 1;
        }
    }

  return 0;
}
\f
/* Utilities for building expressions.
   Since complex expressions are recorded as symbols for use in other
   expressions these return a symbolS * and not an expressionS *.
   These explicitly do not take an "add_number" argument.  */
/* ??? For completeness' sake one might want expr_build_symbol.
   It would just return its argument.  */

/* Build an expression for an unsigned constant.
   The corresponding one for signed constants is missing because
   there's currently no need for it.  One could add an unsigned_p flag
   but that seems more clumsy.  */

symbolS *
expr_build_uconstant (value)
     offsetT value;
{
  expressionS e;

  e.X_op = O_constant;
  e.X_add_number = value;
  e.X_unsigned = 1;
  return make_expr_symbol (&e);
}

/* Build an expression for OP s1.  */

symbolS *
expr_build_unary (op, s1)
     operatorT op;
     symbolS *s1;
{
  expressionS e;

  e.X_op = op;
  e.X_add_symbol = s1;
  e.X_add_number = 0;
  return make_expr_symbol (&e);
}

/* Build an expression for s1 OP s2.  */

symbolS *
expr_build_binary (op, s1, s2)
     operatorT op;
     symbolS *s1;
     symbolS *s2;
{
  expressionS e;

  e.X_op = op;
  e.X_add_symbol = s1;
  e.X_op_symbol = s2;
  e.X_add_number = 0;
  return make_expr_symbol (&e);
}

/* Build an expression for the current location ('.').  */

symbolS *
expr_build_dot ()
{
  expressionS e;

  current_location (&e);
  return make_expr_symbol (&e);
}
\f
/* Build any floating-point literal here.
   Also build any bignum literal here.  */

/* Seems atof_machine can backscan through generic_bignum and hit whatever
   happens to be loaded before it in memory.  And its way too complicated
   for me to fix right.  Thus a hack.  JF:  Just make generic_bignum bigger,
   and never write into the early words, thus they'll always be zero.
   I hate Dean's floating-point code.  Bleh.  */
LITTLENUM_TYPE generic_bignum[SIZE_OF_LARGE_NUMBER + 6];

FLONUM_TYPE generic_floating_point_number = {
  &generic_bignum[6],           /* low.  (JF: Was 0)  */
  &generic_bignum[SIZE_OF_LARGE_NUMBER + 6 - 1], /* high.  JF: (added +6)  */
  0,                            /* leader.  */
  0,                            /* exponent.  */
  0                             /* sign.  */
};

/* If nonzero, we've been asked to assemble nan, +inf or -inf.  */
int generic_floating_point_magic;
\f
static void
floating_constant (expressionP)
     expressionS *expressionP;
{
  /* input_line_pointer -> floating-point constant.  */
  int error_code;

  error_code = atof_generic (&input_line_pointer, ".", EXP_CHARS,
                             &generic_floating_point_number);

  if (error_code)
    {
      if (error_code == ERROR_EXPONENT_OVERFLOW)
        {
          as_bad (_("bad floating-point constant: exponent overflow"));
        }
      else
        {
          as_bad (_("bad floating-point constant: unknown error code=%d"),
                  error_code);
        }
    }
  expressionP->X_op = O_big;
  /* input_line_pointer -> just after constant, which may point to
     whitespace.  */
  expressionP->X_add_number = -1;
}

static valueT
generic_bignum_to_int32 ()
{
  valueT number =
           ((generic_bignum[1] & LITTLENUM_MASK) << LITTLENUM_NUMBER_OF_BITS)
           | (generic_bignum[0] & LITTLENUM_MASK);
  number &= 0xffffffff;
  return number;
}

#ifdef BFD64
static valueT
generic_bignum_to_int64 ()
{
  valueT number =
    ((((((((valueT) generic_bignum[3] & LITTLENUM_MASK)
          << LITTLENUM_NUMBER_OF_BITS)
         | ((valueT) generic_bignum[2] & LITTLENUM_MASK))
        << LITTLENUM_NUMBER_OF_BITS)
       | ((valueT) generic_bignum[1] & LITTLENUM_MASK))
      << LITTLENUM_NUMBER_OF_BITS)
     | ((valueT) generic_bignum[0] & LITTLENUM_MASK));
  return number;
}
#endif

static void
integer_constant (radix, expressionP)
     int radix;
     expressionS *expressionP;
{
  char *start;          /* Start of number.  */
  char *suffix = NULL;
  char c;
  valueT number;        /* Offset or (absolute) value.  */
  short int digit;      /* Value of next digit in current radix.  */
  short int maxdig = 0; /* Highest permitted digit value.  */
  int too_many_digits = 0;      /* If we see >= this number of.  */
  char *name;           /* Points to name of symbol.  */
  symbolS *symbolP;     /* Points to symbol.  */

  int small;                    /* True if fits in 32 bits.  */

  /* May be bignum, or may fit in 32 bits.  */
  /* Most numbers fit into 32 bits, and we want this case to be fast.
     so we pretend it will fit into 32 bits.  If, after making up a 32
     bit number, we realise that we have scanned more digits than
     comfortably fit into 32 bits, we re-scan the digits coding them
     into a bignum.  For decimal and octal numbers we are
     conservative: Some numbers may be assumed bignums when in fact
     they do fit into 32 bits.  Numbers of any radix can have excess
     leading zeros: We strive to recognise this and cast them back
     into 32 bits.  We must check that the bignum really is more than
     32 bits, and change it back to a 32-bit number if it fits.  The
     number we are looking for is expected to be positive, but if it
     fits into 32 bits as an unsigned number, we let it be a 32-bit
     number.  The cavalier approach is for speed in ordinary cases.  */
  /* This has been extended for 64 bits.  We blindly assume that if
     you're compiling in 64-bit mode, the target is a 64-bit machine.
     This should be cleaned up.  */

#ifdef BFD64
#define valuesize 64
#else /* includes non-bfd case, mostly */
#define valuesize 32
#endif

  if ((NUMBERS_WITH_SUFFIX || flag_m68k_mri) && radix == 0)
    {
      int flt = 0;

      /* In MRI mode, the number may have a suffix indicating the
         radix.  For that matter, it might actually be a floating
         point constant.  */
      for (suffix = input_line_pointer; ISALNUM (*suffix); suffix++)
        {
          if (*suffix == 'e' || *suffix == 'E')
            flt = 1;
        }

      if (suffix == input_line_pointer)
        {
          radix = 10;
          suffix = NULL;
        }
      else
        {
          c = *--suffix;
          c = TOUPPER (c);
          if (c == 'B')
            radix = 2;
          else if (c == 'D')
            radix = 10;
          else if (c == 'O' || c == 'Q')
            radix = 8;
          else if (c == 'H')
            radix = 16;
          else if (suffix[1] == '.' || c == 'E' || flt)
            {
              floating_constant (expressionP);
              return;
            }
          else
            {
              radix = 10;
              suffix = NULL;
            }
        }
    }

  switch (radix)
    {
    case 2:
      maxdig = 2;
      too_many_digits = valuesize + 1;
      break;
    case 8:
      maxdig = radix = 8;
      too_many_digits = (valuesize + 2) / 3 + 1;
      break;
    case 16:
      maxdig = radix = 16;
      too_many_digits = (valuesize + 3) / 4 + 1;
      break;
    case 10:
      maxdig = radix = 10;
      too_many_digits = (valuesize + 11) / 4; /* Very rough.  */
    }
#undef valuesize
  start = input_line_pointer;
  c = *input_line_pointer++;
  for (number = 0;
       (digit = hex_value (c)) < maxdig;
       c = *input_line_pointer++)
    {
      number = number * radix + digit;
    }
  /* c contains character after number.  */
  /* input_line_pointer->char after c.  */
  small = (input_line_pointer - start - 1) < too_many_digits;

  if (radix == 16 && c == '_')
    {
      /* This is literal of the form 0x333_0_12345678_1.
         This example is equivalent to 0x00000333000000001234567800000001.  */

      int num_little_digits = 0;
      int i;
      input_line_pointer = start;       /* -> 1st digit.  */

      know (LITTLENUM_NUMBER_OF_BITS == 16);

      for (c = '_'; c == '_'; num_little_digits += 2)
        {

          /* Convert one 64-bit word.  */
          int ndigit = 0;
          number = 0;
          for (c = *input_line_pointer++;
               (digit = hex_value (c)) < maxdig;
               c = *(input_line_pointer++))
            {
              number = number * radix + digit;
              ndigit++;
            }

          /* Check for 8 digit per word max.  */
          if (ndigit > 8)
            as_bad (_("a bignum with underscores may not have more than 8 hex digits in any word"));

          /* Add this chunk to the bignum.
             Shift things down 2 little digits.  */
          know (LITTLENUM_NUMBER_OF_BITS == 16);
          for (i = min (num_little_digits + 1, SIZE_OF_LARGE_NUMBER - 1);
               i >= 2;
               i--)
            generic_bignum[i] = generic_bignum[i - 2];

          /* Add the new digits as the least significant new ones.  */
          generic_bignum[0] = number & 0xffffffff;
          generic_bignum[1] = number >> 16;
        }

      /* Again, c is char after number, input_line_pointer->after c.  */

      if (num_little_digits > SIZE_OF_LARGE_NUMBER - 1)
        num_little_digits = SIZE_OF_LARGE_NUMBER - 1;

      assert (num_little_digits >= 4);

      if (num_little_digits != 8)
        as_bad (_("a bignum with underscores must have exactly 4 words"));

      /* We might have some leading zeros.  These can be trimmed to give
         us a change to fit this constant into a small number.  */
      while (generic_bignum[num_little_digits - 1] == 0
             && num_little_digits > 1)
        num_little_digits--;

      if (num_little_digits <= 2)
        {
          /* will fit into 32 bits.  */
          number = generic_bignum_to_int32 ();
          small = 1;
        }
#ifdef BFD64
      else if (num_little_digits <= 4)
        {
          /* Will fit into 64 bits.  */
          number = generic_bignum_to_int64 ();
          small = 1;
        }
#endif
      else
        {
          small = 0;

          /* Number of littlenums in the bignum.  */
          number = num_little_digits;
        }
    }
  else if (!small)
    {
      /* We saw a lot of digits. manufacture a bignum the hard way.  */
      LITTLENUM_TYPE *leader;   /* -> high order littlenum of the bignum.  */
      LITTLENUM_TYPE *pointer;  /* -> littlenum we are frobbing now.  */
      long carry;

      leader = generic_bignum;
      generic_bignum[0] = 0;
      generic_bignum[1] = 0;
      generic_bignum[2] = 0;
      generic_bignum[3] = 0;
      input_line_pointer = start;       /* -> 1st digit.  */
      c = *input_line_pointer++;
      for (; (carry = hex_value (c)) < maxdig; c = *input_line_pointer++)
        {
          for (pointer = generic_bignum; pointer <= leader; pointer++)
            {
              long work;

              work = carry + radix * *pointer;
              *pointer = work & LITTLENUM_MASK;
              carry = work >> LITTLENUM_NUMBER_OF_BITS;
            }
          if (carry)
            {
              if (leader < generic_bignum + SIZE_OF_LARGE_NUMBER - 1)
                {
                  /* Room to grow a longer bignum.  */
                  *++leader = carry;
                }
            }
        }
      /* Again, c is char after number.  */
      /* input_line_pointer -> after c.  */
      know (LITTLENUM_NUMBER_OF_BITS == 16);
      if (leader < generic_bignum + 2)
        {
          /* Will fit into 32 bits.  */
          number = generic_bignum_to_int32 ();
          small = 1;
        }
#ifdef BFD64
      else if (leader < generic_bignum + 4)
        {
          /* Will fit into 64 bits.  */
          number = generic_bignum_to_int64 ();
          small = 1;
        }
#endif
      else
        {
          /* Number of littlenums in the bignum.  */
          number = leader - generic_bignum + 1;
        }
    }

  if ((NUMBERS_WITH_SUFFIX || flag_m68k_mri)
      && suffix != NULL
      && input_line_pointer - 1 == suffix)
    c = *input_line_pointer++;

  if (small)
    {
      /* Here with number, in correct radix. c is the next char.
         Note that unlike un*x, we allow "011f" "0x9f" to both mean
         the same as the (conventional) "9f".
         This is simply easier than checking for strict canonical
         form.  Syntax sux!  */

      if (LOCAL_LABELS_FB && c == 'b')
        {
          /* Backward ref to local label.
             Because it is backward, expect it to be defined.  */
          /* Construct a local label.  */
          name = fb_label_name ((int) number, 0);

          /* Seen before, or symbol is defined: OK.  */
          symbolP = symbol_find (name);
          if ((symbolP != NULL) && (S_IS_DEFINED (symbolP)))
            {
              /* Local labels are never absolute.  Don't waste time
                 checking absoluteness.  */
              know (SEG_NORMAL (S_GET_SEGMENT (symbolP)));

              expressionP->X_op = O_symbol;
              expressionP->X_add_symbol = symbolP;
            }
          else
            {
              /* Either not seen or not defined.  */
              /* @@ Should print out the original string instead of
                 the parsed number.  */
              as_bad (_("backward ref to unknown label \"%d:\""),
                      (int) number);
              expressionP->X_op = O_constant;
            }

          expressionP->X_add_number = 0;
        }                       /* case 'b' */
      else if (LOCAL_LABELS_FB && c == 'f')
        {
          /* Forward reference.  Expect symbol to be undefined or
             unknown.  undefined: seen it before.  unknown: never seen
             it before.

             Construct a local label name, then an undefined symbol.
             Don't create a xseg frag for it: caller may do that.
             Just return it as never seen before.  */
          name = fb_label_name ((int) number, 1);
          symbolP = symbol_find_or_make (name);
          /* We have no need to check symbol properties.  */
#ifndef many_segments
          /* Since "know" puts its arg into a "string", we
             can't have newlines in the argument.  */
          know (S_GET_SEGMENT (symbolP) == undefined_section || S_GET_SEGMENT (symbolP) == text_section || S_GET_SEGMENT (symbolP) == data_section);
#endif
          expressionP->X_op = O_symbol;
          expressionP->X_add_symbol = symbolP;
          expressionP->X_add_number = 0;
        }                       /* case 'f' */
      else if (LOCAL_LABELS_DOLLAR && c == '$')
        {
          /* If the dollar label is *currently* defined, then this is just
             another reference to it.  If it is not *currently* defined,
             then this is a fresh instantiation of that number, so create
             it.  */

          if (dollar_label_defined ((long) number))
            {
              name = dollar_label_name ((long) number, 0);
              symbolP = symbol_find (name);
              know (symbolP != NULL);
            }
          else
            {
              name = dollar_label_name ((long) number, 1);
              symbolP = symbol_find_or_make (name);
            }

          expressionP->X_op = O_symbol;
          expressionP->X_add_symbol = symbolP;
          expressionP->X_add_number = 0;
        }                       /* case '$' */
      else
        {
          expressionP->X_op = O_constant;
#ifdef TARGET_WORD_SIZE
          /* Sign extend NUMBER.  */
          number |= (-(number >> (TARGET_WORD_SIZE - 1))) << (TARGET_WORD_SIZE - 1);
#endif
          expressionP->X_add_number = number;
          input_line_pointer--; /* Restore following character.  */
        }                       /* Really just a number.  */
    }
  else
    {
      /* Not a small number.  */
      expressionP->X_op = O_big;
      expressionP->X_add_number = number;       /* Number of littlenums.  */
      input_line_pointer--;     /* -> char following number.  */
    }
}

/* Parse an MRI multi character constant.  */

static void
mri_char_constant (expressionP)
     expressionS *expressionP;
{
  int i;

  if (*input_line_pointer == '\''
      && input_line_pointer[1] != '\'')
    {
      expressionP->X_op = O_constant;
      expressionP->X_add_number = 0;
      return;
    }

  /* In order to get the correct byte ordering, we must build the
     number in reverse.  */
  for (i = SIZE_OF_LARGE_NUMBER - 1; i >= 0; i--)
    {
      int j;

      generic_bignum[i] = 0;
      for (j = 0; j < CHARS_PER_LITTLENUM; j++)
        {
          if (*input_line_pointer == '\'')
            {
              if (input_line_pointer[1] != '\'')
                break;
              ++input_line_pointer;
            }
          generic_bignum[i] <<= 8;
          generic_bignum[i] += *input_line_pointer;
          ++input_line_pointer;
        }

      if (i < SIZE_OF_LARGE_NUMBER - 1)
        {
          /* If there is more than one littlenum, left justify the
             last one to make it match the earlier ones.  If there is
             only one, we can just use the value directly.  */
          for (; j < CHARS_PER_LITTLENUM; j++)
            generic_bignum[i] <<= 8;
        }

      if (*input_line_pointer == '\''
          && input_line_pointer[1] != '\'')
        break;
    }

  if (i < 0)
    {
      as_bad (_("character constant too large"));
      i = 0;
    }

  if (i > 0)
    {
      int c;
      int j;

      c = SIZE_OF_LARGE_NUMBER - i;
      for (j = 0; j < c; j++)
        generic_bignum[j] = generic_bignum[i + j];
      i = c;
    }

  know (LITTLENUM_NUMBER_OF_BITS == 16);
  if (i > 2)
    {
      expressionP->X_op = O_big;
      expressionP->X_add_number = i;
    }
  else
    {
      expressionP->X_op = O_constant;
      if (i < 2)
        expressionP->X_add_number = generic_bignum[0] & LITTLENUM_MASK;
      else
        expressionP->X_add_number =
          (((generic_bignum[1] & LITTLENUM_MASK)
            << LITTLENUM_NUMBER_OF_BITS)
           | (generic_bignum[0] & LITTLENUM_MASK));
    }

  /* Skip the final closing quote.  */
  ++input_line_pointer;
}

/* Return an expression representing the current location.  This
   handles the magic symbol `.'.  */

static void
current_location (expressionp)
     expressionS *expressionp;
{
  if (now_seg == absolute_section)
    {
      expressionp->X_op = O_constant;
      expressionp->X_add_number = abs_section_offset;
    }
  else
    {
      symbolS *symbolp;

      symbolp = symbol_new (FAKE_LABEL_NAME, now_seg,
                            (valueT) frag_now_fix (),
                            frag_now);
      expressionp->X_op = O_symbol;
      expressionp->X_add_symbol = symbolp;
      expressionp->X_add_number = 0;
    }
}

/* In:  Input_line_pointer points to 1st char of operand, which may
        be a space.

   Out: An expressionS.
        The operand may have been empty: in this case X_op == O_absent.
        Input_line_pointer->(next non-blank) char after operand.  */

static segT
operand (expressionP)
     expressionS *expressionP;
{
  char c;
  symbolS *symbolP;     /* Points to symbol.  */
  char *name;           /* Points to name of symbol.  */
  segT segment;

  /* All integers are regarded as unsigned unless they are negated.
     This is because the only thing which cares whether a number is
     unsigned is the code in emit_expr which extends constants into
     bignums.  It should only sign extend negative numbers, so that
     something like ``.quad 0x80000000'' is not sign extended even
     though it appears negative if valueT is 32 bits.  */
  expressionP->X_unsigned = 1;

  /* Digits, assume it is a bignum.  */

  SKIP_WHITESPACE ();           /* Leading whitespace is part of operand.  */
  c = *input_line_pointer++;    /* input_line_pointer -> past char in c.  */

  if (is_end_of_line[(unsigned char) c])
    goto eol;

  switch (c)
    {
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
    case '8':
    case '9':
      input_line_pointer--;

      integer_constant ((NUMBERS_WITH_SUFFIX || flag_m68k_mri)
                        ? 0 : 10,
                        expressionP);
      break;

#ifdef LITERAL_PREFIXDOLLAR_HEX
    case '$':
      /* $L is the start of a local label, not a hex constant.  */
      if (* input_line_pointer == 'L')
      goto isname;
      integer_constant (16, expressionP);
      break;
#endif

#ifdef LITERAL_PREFIXPERCENT_BIN
    case '%':
      integer_constant (2, expressionP);
      break;
#endif

    case '0':
      /* Non-decimal radix.  */

      if (NUMBERS_WITH_SUFFIX || flag_m68k_mri)
        {
          char *s;

          /* Check for a hex constant.  */
          for (s = input_line_pointer; hex_p (*s); s++)
            ;
          if (*s == 'h' || *s == 'H')
            {
              --input_line_pointer;
              integer_constant (0, expressionP);
              break;
            }
        }
      c = *input_line_pointer;
      switch (c)
        {
        case 'o':
        case 'O':
        case 'q':
        case 'Q':
        case '8':
        case '9':
          if (NUMBERS_WITH_SUFFIX || flag_m68k_mri)
            {
              integer_constant (0, expressionP);
              break;
            }
          /* Fall through.  */
        default:
        default_case:
          if (c && strchr (FLT_CHARS, c))
            {
              input_line_pointer++;
              floating_constant (expressionP);
              expressionP->X_add_number = - TOLOWER (c);
            }
          else
            {
              /* The string was only zero.  */
              expressionP->X_op = O_constant;
              expressionP->X_add_number = 0;
            }

          break;

        case 'x':
        case 'X':
          if (flag_m68k_mri)
            goto default_case;
          input_line_pointer++;
          integer_constant (16, expressionP);
          break;

        case 'b':
          if (LOCAL_LABELS_FB && ! (flag_m68k_mri || NUMBERS_WITH_SUFFIX))
            {
              /* This code used to check for '+' and '-' here, and, in
                 some conditions, fall through to call
                 integer_constant.  However, that didn't make sense,
                 as integer_constant only accepts digits.  */
              /* Some of our code elsewhere does permit digits greater
                 than the expected base; for consistency, do the same
                 here.  */
              if (input_line_pointer[1] < '0'
                  || input_line_pointer[1] > '9')
                {
                  /* Parse this as a back reference to label 0.  */
                  input_line_pointer--;
                  integer_constant (10, expressionP);
                  break;
                }
              /* Otherwise, parse this as a binary number.  */
            }
          /* Fall through.  */
        case 'B':
          input_line_pointer++;
          if (flag_m68k_mri || NUMBERS_WITH_SUFFIX)
            goto default_case;
          integer_constant (2, expressionP);
          break;

        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
          integer_constant ((flag_m68k_mri || NUMBERS_WITH_SUFFIX)
                            ? 0 : 8,
                            expressionP);
          break;

        case 'f':
          if (LOCAL_LABELS_FB)
            {
              /* If it says "0f" and it could possibly be a floating point
                 number, make it one.  Otherwise, make it a local label,
                 and try to deal with parsing the rest later.  */
              if (!input_line_pointer[1]
                  || (is_end_of_line[0xff & input_line_pointer[1]])
                  || strchr (FLT_CHARS, 'f') == NULL)
                goto is_0f_label;
              {
                char *cp = input_line_pointer + 1;
                int r = atof_generic (&cp, ".", EXP_CHARS,
                                      &generic_floating_point_number);
                switch (r)
                  {
                  case 0:
                  case ERROR_EXPONENT_OVERFLOW:
                    if (*cp == 'f' || *cp == 'b')
                      /* Looks like a difference expression.  */
                      goto is_0f_label;
                    else if (cp == input_line_pointer + 1)
                      /* No characters has been accepted -- looks like
                         end of operand.  */
                      goto is_0f_label;
                    else
                      goto is_0f_float;
                  default:
                    as_fatal (_("expr.c(operand): bad atof_generic return val %d"),
                              r);
                  }
              }

              /* Okay, now we've sorted it out.  We resume at one of these
                 two labels, depending on what we've decided we're probably
                 looking at.  */
            is_0f_label:
              input_line_pointer--;
              integer_constant (10, expressionP);
              break;

            is_0f_float:
              /* Fall through.  */
              ;
            }

        case 'd':
        case 'D':
          if (flag_m68k_mri || NUMBERS_WITH_SUFFIX)
            {
              integer_constant (0, expressionP);
              break;
            }
          /* Fall through.  */
        case 'F':
        case 'r':
        case 'e':
        case 'E':
        case 'g':
        case 'G':
          input_line_pointer++;
          floating_constant (expressionP);
          expressionP->X_add_number = - TOLOWER (c);
          break;

        case '$':
          if (LOCAL_LABELS_DOLLAR)
            {
              integer_constant (10, expressionP);
              break;
            }
          else
            goto default_case;
        }

      break;

    case '(':
#ifndef NEED_INDEX_OPERATOR
    case '[':
#endif
      /* Didn't begin with digit & not a name.  */
      segment = expression (expressionP);
      /* expression () will pass trailing whitespace.  */
      if ((c == '(' && *input_line_pointer != ')')
          || (c == '[' && *input_line_pointer != ']'))
        {
#ifdef RELAX_PAREN_GROUPING
          if (c != '(')
#endif
            as_bad (_("missing '%c'"), c == '(' ? ')' : ']');
        }
      else
        input_line_pointer++;
      SKIP_WHITESPACE ();
      /* Here with input_line_pointer -> char after "(...)".  */
      return segment;

#ifdef TC_M68K
    case 'E':
      if (! flag_m68k_mri || *input_line_pointer != '\'')
        goto de_fault;
      as_bad (_("EBCDIC constants are not supported"));
      /* Fall through.  */
    case 'A':
      if (! flag_m68k_mri || *input_line_pointer != '\'')
        goto de_fault;
      ++input_line_pointer;
      /* Fall through.  */
#endif
    case '\'':
      if (! flag_m68k_mri)
        {
          /* Warning: to conform to other people's assemblers NO
             ESCAPEMENT is permitted for a single quote.  The next
             character, parity errors and all, is taken as the value
             of the operand.  VERY KINKY.  */
          expressionP->X_op = O_constant;
          expressionP->X_add_number = *input_line_pointer++;
          break;
        }

      mri_char_constant (expressionP);
      break;

    case '+':
      (void) operand (expressionP);
      break;

#ifdef TC_M68K
    case '"':
      /* Double quote is the bitwise not operator in MRI mode.  */
      if (! flag_m68k_mri)
        goto de_fault;
      /* Fall through.  */
#endif
    case '~':
      /* '~' is permitted to start a label on the Delta.  */
      if (is_name_beginner (c))
        goto isname;
    case '!':
    case '-':
      {
        operand (expressionP);
        if (expressionP->X_op == O_constant)
          {
            /* input_line_pointer -> char after operand.  */
            if (c == '-')
              {
                expressionP->X_add_number = - expressionP->X_add_number;
                /* Notice: '-' may overflow: no warning is given.
                   This is compatible with other people's
                   assemblers.  Sigh.  */
                expressionP->X_unsigned = 0;
              }
            else if (c == '~' || c == '"')
              expressionP->X_add_number = ~ expressionP->X_add_number;
            else
              expressionP->X_add_number = ! expressionP->X_add_number;
          }
        else if (expressionP->X_op != O_illegal
                 && expressionP->X_op != O_absent)
          {
            expressionP->X_add_symbol = make_expr_symbol (expressionP);
            if (c == '-')
              expressionP->X_op = O_uminus;
            else if (c == '~' || c == '"')
              expressionP->X_op = O_bit_not;
            else
              expressionP->X_op = O_logical_not;
            expressionP->X_add_number = 0;
          }
        else
          as_warn (_("Unary operator %c ignored because bad operand follows"),
                   c);
      }
      break;

#if defined (DOLLAR_DOT) || defined (TC_M68K)
    case '$':
      /* '$' is the program counter when in MRI mode, or when
         DOLLAR_DOT is defined.  */
#ifndef DOLLAR_DOT
      if (! flag_m68k_mri)
        goto de_fault;
#endif
      if (flag_m68k_mri && hex_p (*input_line_pointer))
        {
          /* In MRI mode, '$' is also used as the prefix for a
             hexadecimal constant.  */
          integer_constant (16, expressionP);
          break;
        }

      if (is_part_of_name (*input_line_pointer))
        goto isname;

      current_location (expressionP);
      break;
#endif

    case '.':
      if (!is_part_of_name (*input_line_pointer))
        {
          current_location (expressionP);
          break;
        }
      else if ((strncasecmp (input_line_pointer, "startof.", 8) == 0
                && ! is_part_of_name (input_line_pointer[8]))
               || (strncasecmp (input_line_pointer, "sizeof.", 7) == 0
                   && ! is_part_of_name (input_line_pointer[7])))
        {
          int start;

          start = (input_line_pointer[1] == 't'
                   || input_line_pointer[1] == 'T');
          input_line_pointer += start ? 8 : 7;
          SKIP_WHITESPACE ();
          if (*input_line_pointer != '(')
            as_bad (_("syntax error in .startof. or .sizeof."));
          else
            {
              char *buf;

              ++input_line_pointer;
              SKIP_WHITESPACE ();
              name = input_line_pointer;
              c = get_symbol_end ();

              buf = (char *) xmalloc (strlen (name) + 10);
              if (start)
                sprintf (buf, ".startof.%s", name);
              else
                sprintf (buf, ".sizeof.%s", name);
              symbolP = symbol_make (buf);
              free (buf);

              expressionP->X_op = O_symbol;
              expressionP->X_add_symbol = symbolP;
              expressionP->X_add_number = 0;

              *input_line_pointer = c;
              SKIP_WHITESPACE ();
              if (*input_line_pointer != ')')
                as_bad (_("syntax error in .startof. or .sizeof."));
              else
                ++input_line_pointer;
            }
          break;
        }
      else
        {
          goto isname;
        }

    case ',':
    eol:
      /* Can't imagine any other kind of operand.  */
      expressionP->X_op = O_absent;
      input_line_pointer--;
      break;

#ifdef TC_M68K
    case '%':
      if (! flag_m68k_mri)
        goto de_fault;
      integer_constant (2, expressionP);
      break;

    case '@':
      if (! flag_m68k_mri)
        goto de_fault;
      integer_constant (8, expressionP);
      break;

    case ':':
      if (! flag_m68k_mri)
        goto de_fault;

      /* In MRI mode, this is a floating point constant represented
         using hexadecimal digits.  */

      ++input_line_pointer;
      integer_constant (16, expressionP);
      break;

    case '*':
      if (! flag_m68k_mri || is_part_of_name (*input_line_pointer))
        goto de_fault;

      current_location (expressionP);
      break;
#endif

    default:
#ifdef TC_M68K
    de_fault:
#endif
      if (is_name_beginner (c)) /* Here if did not begin with a digit.  */
        {
          /* Identifier begins here.
             This is kludged for speed, so code is repeated.  */
        isname:
          name = --input_line_pointer;
          c = get_symbol_end ();

#ifdef md_parse_name
          /* This is a hook for the backend to parse certain names
             specially in certain contexts.  If a name always has a
             specific value, it can often be handled by simply
             entering it in the symbol table.  */
          if (md_parse_name (name, expressionP, &c))
            {
              *input_line_pointer = c;
              break;
            }
#endif

#ifdef TC_I960
          /* The MRI i960 assembler permits
                 lda sizeof code,g13
             FIXME: This should use md_parse_name.  */
          if (flag_mri
              && (strcasecmp (name, "sizeof") == 0
                  || strcasecmp (name, "startof") == 0))
            {
              int start;
              char *buf;

              start = (name[1] == 't'
                       || name[1] == 'T');

              *input_line_pointer = c;
              SKIP_WHITESPACE ();

              name = input_line_pointer;
              c = get_symbol_end ();

              buf = (char *) xmalloc (strlen (name) + 10);
              if (start)
                sprintf (buf, ".startof.%s", name);
              else
                sprintf (buf, ".sizeof.%s", name);
              symbolP = symbol_make (buf);
              free (buf);

              expressionP->X_op = O_symbol;
              expressionP->X_add_symbol = symbolP;
              expressionP->X_add_number = 0;

              *input_line_pointer = c;
              SKIP_WHITESPACE ();

              break;
            }
#endif

          symbolP = symbol_find_or_make (name);

          /* If we have an absolute symbol or a reg, then we know its
             value now.  */
          segment = S_GET_SEGMENT (symbolP);
          if (segment == absolute_section)
            {
              expressionP->X_op = O_constant;
              expressionP->X_add_number = S_GET_VALUE (symbolP);
            }
          else if (segment == reg_section)
            {
              expressionP->X_op = O_register;
              expressionP->X_add_number = S_GET_VALUE (symbolP);
            }
          else
            {
              expressionP->X_op = O_symbol;
              expressionP->X_add_symbol = symbolP;
              expressionP->X_add_number = 0;
            }
          *input_line_pointer = c;
        }
      else
        {
          /* Let the target try to parse it.  Success is indicated by changing
             the X_op field to something other than O_absent and pointing
             input_line_pointer past the expression.  If it can't parse the
             expression, X_op and input_line_pointer should be unchanged.  */
          expressionP->X_op = O_absent;
          --input_line_pointer;
          md_operand (expressionP);
          if (expressionP->X_op == O_absent)
            {
              ++input_line_pointer;
              as_bad (_("bad expression"));
              expressionP->X_op = O_constant;
              expressionP->X_add_number = 0;
            }
        }
      break;
    }

  /* It is more 'efficient' to clean up the expressionS when they are
     created.  Doing it here saves lines of code.  */
  clean_up_expression (expressionP);
  SKIP_WHITESPACE ();           /* -> 1st char after operand.  */
  know (*input_line_pointer != ' ');

  /* The PA port needs this information.  */
  if (expressionP->X_add_symbol)
    symbol_mark_used (expressionP->X_add_symbol);

  switch (expressionP->X_op)
    {
    default:
      return absolute_section;
    case O_symbol:
      return S_GET_SEGMENT (expressionP->X_add_symbol);
    case O_register:
      return reg_section;
    }
}
\f
/* Internal.  Simplify a struct expression for use by expr ().  */

/* In:  address of an expressionS.
        The X_op field of the expressionS may only take certain values.
        Elsewise we waste time special-case testing. Sigh. Ditto SEG_ABSENT.

   Out: expressionS may have been modified:
        Unused fields zeroed to help expr ().  */

static void
clean_up_expression (expressionP)
     expressionS *expressionP;
{
  switch (expressionP->X_op)
    {
    case O_illegal:
    case O_absent:
      expressionP->X_add_number = 0;
      /* Fall through.  */
    case O_big:
    case O_constant:
    case O_register:
      expressionP->X_add_symbol = NULL;
      /* Fall through.  */
    case O_symbol:
    case O_uminus:
    case O_bit_not:
      expressionP->X_op_symbol = NULL;
      break;
    default:
      break;
    }
}
\f
/* Expression parser.  */

/* We allow an empty expression, and just assume (absolute,0) silently.
   Unary operators and parenthetical expressions are treated as operands.
   As usual, Q==quantity==operand, O==operator, X==expression mnemonics.

   We used to do an aho/ullman shift-reduce parser, but the logic got so
   warped that I flushed it and wrote a recursive-descent parser instead.
   Now things are stable, would anybody like to write a fast parser?
   Most expressions are either register (which does not even reach here)
   or 1 symbol. Then "symbol+constant" and "symbol-symbol" are common.
   So I guess it doesn't really matter how inefficient more complex expressions
   are parsed.

   After expr(RANK,resultP) input_line_pointer->operator of rank <= RANK.
   Also, we have consumed any leading or trailing spaces (operand does that)
   and done all intervening operators.

   This returns the segment of the result, which will be
   absolute_section or the segment of a symbol.  */

#undef __
#define __ O_illegal

/* Maps ASCII -> operators.  */
static const operatorT op_encoding[256] = {
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,

  __, O_bit_or_not, __, __, __, O_modulus, O_bit_and, __,
  __, __, O_multiply, O_add, __, O_subtract, __, O_divide,
  __, __, __, __, __, __, __, __,
  __, __, __, __, O_lt, __, O_gt, __,
  __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __,
  __, __, __,
#ifdef NEED_INDEX_OPERATOR
  O_index,
#else
  __,
#endif
  __, __, O_bit_exclusive_or, __,
  __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __,
  __, __, __, __, O_bit_inclusive_or, __, __, __,

  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
  __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __
};

/* Rank Examples
   0    operand, (expression)
   1    ||
   2    &&
   3    == <> < <= >= >
   4    + -
   5    used for * / % in MRI mode
   6    & ^ ! |
   7    * / % << >>
   8    unary - unary ~
*/
static operator_rankT op_rank[] = {
  0,    /* O_illegal */
  0,    /* O_absent */
  0,    /* O_constant */
  0,    /* O_symbol */
  0,    /* O_symbol_rva */
  0,    /* O_register */
  0,    /* O_big */
  9,    /* O_uminus */
  9,    /* O_bit_not */
  9,    /* O_logical_not */
  8,    /* O_multiply */
  8,    /* O_divide */
  8,    /* O_modulus */
  8,    /* O_left_shift */
  8,    /* O_right_shift */
  7,    /* O_bit_inclusive_or */
  7,    /* O_bit_or_not */
  7,    /* O_bit_exclusive_or */
  7,    /* O_bit_and */
  5,    /* O_add */
  5,    /* O_subtract */
  4,    /* O_eq */
  4,    /* O_ne */
  4,    /* O_lt */
  4,    /* O_le */
  4,    /* O_ge */
  4,    /* O_gt */
  3,    /* O_logical_and */
  2,    /* O_logical_or */
  1,    /* O_index */
  0,    /* O_md1 */
  0,    /* O_md2 */
  0,    /* O_md3 */
  0,    /* O_md4 */
  0,    /* O_md5 */
  0,    /* O_md6 */
  0,    /* O_md7 */
  0,    /* O_md8 */
  0,    /* O_md9 */
  0,    /* O_md10 */
  0,    /* O_md11 */
  0,    /* O_md12 */
  0,    /* O_md13 */
  0,    /* O_md14 */
  0,    /* O_md15 */
  0,    /* O_md16 */
};

/* Unfortunately, in MRI mode for the m68k, multiplication and
   division have lower precedence than the bit wise operators.  This
   function sets the operator precedences correctly for the current
   mode.  Also, MRI uses a different bit_not operator, and this fixes
   that as well.  */

#define STANDARD_MUL_PRECEDENCE 8
#define MRI_MUL_PRECEDENCE 6

void
expr_set_precedence ()
{
  if (flag_m68k_mri)
    {
      op_rank[O_multiply] = MRI_MUL_PRECEDENCE;
      op_rank[O_divide] = MRI_MUL_PRECEDENCE;
      op_rank[O_modulus] = MRI_MUL_PRECEDENCE;
    }
  else
    {
      op_rank[O_multiply] = STANDARD_MUL_PRECEDENCE;
      op_rank[O_divide] = STANDARD_MUL_PRECEDENCE;
      op_rank[O_modulus] = STANDARD_MUL_PRECEDENCE;
    }
}

/* Initialize the expression parser.  */

void
expr_begin ()
{
  expr_set_precedence ();

  /* Verify that X_op field is wide enough.  */
  {
    expressionS e;
    e.X_op = O_max;
    assert (e.X_op == O_max);
  }
}
\f
/* Return the encoding for the operator at INPUT_LINE_POINTER, and
   sets NUM_CHARS to the number of characters in the operator.
   Does not advance INPUT_LINE_POINTER.  */

static inline operatorT
operator (num_chars)
     int *num_chars;
{
  int c;
  operatorT ret;

  c = *input_line_pointer & 0xff;
  *num_chars = 1;

  if (is_end_of_line[c])
    return O_illegal;

  switch (c)
    {
    default:
      return op_encoding[c];

    case '<':
      switch (input_line_pointer[1])
        {
        default:
          return op_encoding[c];
        case '<':
          ret = O_left_shift;
          break;
        case '>':
          ret = O_ne;
          break;
        case '=':
          ret = O_le;
          break;
        }
      *num_chars = 2;
      return ret;

    case '=':
      if (input_line_pointer[1] != '=')
        return op_encoding[c];

      *num_chars = 2;
      return O_eq;

    case '>':
      switch (input_line_pointer[1])
        {
        default:
          return op_encoding[c];
        case '>':
          ret = O_right_shift;
          break;
        case '=':
          ret = O_ge;
          break;
        }
      *num_chars = 2;
      return ret;

    case '!':
      /* We accept !! as equivalent to ^ for MRI compatibility.  */
      if (input_line_pointer[1] != '!')
        {
          if (flag_m68k_mri)
            return O_bit_inclusive_or;
          return op_encoding[c];
        }
      *num_chars = 2;
      return O_bit_exclusive_or;

    case '|':
      if (input_line_pointer[1] != '|')
        return op_encoding[c];

      *num_chars = 2;
      return O_logical_or;

    case '&':
      if (input_line_pointer[1] != '&')
        return op_encoding[c];

      *num_chars = 2;
      return O_logical_and;
    }

  /* NOTREACHED  */
}

/* Parse an expression.  */

segT
expr (rankarg, resultP)
     int rankarg;       /* Larger # is higher rank.  */
     expressionS *resultP;      /* Deliver result here.  */
{
  operator_rankT rank = (operator_rankT) rankarg;
  segT retval;
  expressionS right;
  operatorT op_left;
  operatorT op_right;
  int op_chars;

  know (rank >= 0);

  /* Save the value of dot for the fixup code.  */
  if (rank == 0)
    dot_value = frag_now_fix ();

  retval = operand (resultP);

  /* operand () gobbles spaces.  */
  know (*input_line_pointer != ' ');

  op_left = operator (&op_chars);
  while (op_left != O_illegal && op_rank[(int) op_left] > rank)
    {
      segT rightseg;

      input_line_pointer += op_chars;   /* -> after operator.  */

      rightseg = expr (op_rank[(int) op_left], &right);
      if (right.X_op == O_absent)
        {
          as_warn (_("missing operand; zero assumed"));
          right.X_op = O_constant;
          right.X_add_number = 0;
          right.X_add_symbol = NULL;
          right.X_op_symbol = NULL;
        }

      know (*input_line_pointer != ' ');

      if (op_left == O_index)
        {
          if (*input_line_pointer != ']')
            as_bad ("missing right bracket");
          else
            {
              ++input_line_pointer;
              SKIP_WHITESPACE ();
            }
        }

      op_right = operator (&op_chars);

      know (op_right == O_illegal
            || op_rank[(int) op_right] <= op_rank[(int) op_left]);
      know ((int) op_left >= (int) O_multiply
            && (int) op_left <= (int) O_logical_or);

      /* input_line_pointer->after right-hand quantity.  */
      /* left-hand quantity in resultP.  */
      /* right-hand quantity in right.  */
      /* operator in op_left.  */

      if (resultP->X_op == O_big)
        {
          if (resultP->X_add_number > 0)
            as_warn (_("left operand is a bignum; integer 0 assumed"));
          else
            as_warn (_("left operand is a float; integer 0 assumed"));
          resultP->X_op = O_constant;
          resultP->X_add_number = 0;
          resultP->X_add_symbol = NULL;
          resultP->X_op_symbol = NULL;
        }
      if (right.X_op == O_big)
        {
          if (right.X_add_number > 0)
            as_warn (_("right operand is a bignum; integer 0 assumed"));
          else
            as_warn (_("right operand is a float; integer 0 assumed"));
          right.X_op = O_constant;
          right.X_add_number = 0;
          right.X_add_symbol = NULL;
          right.X_op_symbol = NULL;
        }

      /* Optimize common cases.  */
#ifdef md_optimize_expr
      if (md_optimize_expr (resultP, op_left, &right))
        {
          /* Skip.  */
          ;
        }
      else
#endif
      if (op_left == O_add && right.X_op == O_constant)
        {
          /* X + constant.  */
          resultP->X_add_number += right.X_add_number;
        }
      /* This case comes up in PIC code.  */
      else if (op_left == O_subtract
               && right.X_op == O_symbol
               && resultP->X_op == O_symbol
               && (symbol_get_frag (right.X_add_symbol)
                   == symbol_get_frag (resultP->X_add_symbol))
               && (SEG_NORMAL (rightseg)
                   || right.X_add_symbol == resultP->X_add_symbol))
        {
          resultP->X_add_number -= right.X_add_number;
          resultP->X_add_number += (S_GET_VALUE (resultP->X_add_symbol)
                                    - S_GET_VALUE (right.X_add_symbol));
          resultP->X_op = O_constant;
          resultP->X_add_symbol = 0;
        }
      else if (op_left == O_subtract && right.X_op == O_constant)
        {
          /* X - constant.  */
          resultP->X_add_number -= right.X_add_number;
        }
      else if (op_left == O_add && resultP->X_op == O_constant)
        {
          /* Constant + X.  */
          resultP->X_op = right.X_op;
          resultP->X_add_symbol = right.X_add_symbol;
          resultP->X_op_symbol = right.X_op_symbol;
          resultP->X_add_number += right.X_add_number;
          retval = rightseg;
        }
      else if (resultP->X_op == O_constant && right.X_op == O_constant)
        {
          /* Constant OP constant.  */
          offsetT v = right.X_add_number;
          if (v == 0 && (op_left == O_divide || op_left == O_modulus))
            {
              as_warn (_("division by zero"));
              v = 1;
            }
          switch (op_left)
            {
            default:                    abort ();
            case O_multiply:            resultP->X_add_number *= v; break;
            case O_divide:              resultP->X_add_number /= v; break;
            case O_modulus:             resultP->X_add_number %= v; break;
            case O_left_shift:          resultP->X_add_number <<= v; break;
            case O_right_shift:
              /* We always use unsigned shifts, to avoid relying on
                 characteristics of the compiler used to compile gas.  */
              resultP->X_add_number =
                (offsetT) ((valueT) resultP->X_add_number >> (valueT) v);
              break;
            case O_bit_inclusive_or:    resultP->X_add_number |= v; break;
            case O_bit_or_not:          resultP->X_add_number |= ~v; break;
            case O_bit_exclusive_or:    resultP->X_add_number ^= v; break;
            case O_bit_and:             resultP->X_add_number &= v; break;
            case O_add:                 resultP->X_add_number += v; break;
            case O_subtract:            resultP->X_add_number -= v; break;
            case O_eq:
              resultP->X_add_number =
                resultP->X_add_number == v ? ~ (offsetT) 0 : 0;
              break;
            case O_ne:
              resultP->X_add_number =
                resultP->X_add_number != v ? ~ (offsetT) 0 : 0;
              break;
            case O_lt:
              resultP->X_add_number =
                resultP->X_add_number <  v ? ~ (offsetT) 0 : 0;
              break;
            case O_le:
              resultP->X_add_number =
                resultP->X_add_number <= v ? ~ (offsetT) 0 : 0;
              break;
            case O_ge:
              resultP->X_add_number =
                resultP->X_add_number >= v ? ~ (offsetT) 0 : 0;
              break;
            case O_gt:
              resultP->X_add_number =
                resultP->X_add_number >  v ? ~ (offsetT) 0 : 0;
              break;
            case O_logical_and:
              resultP->X_add_number = resultP->X_add_number && v;
              break;
            case O_logical_or:
              resultP->X_add_number = resultP->X_add_number || v;
              break;
            }
        }
      else if (resultP->X_op == O_symbol
               && right.X_op == O_symbol
               && (op_left == O_add
                   || op_left == O_subtract
                   || (resultP->X_add_number == 0
                       && right.X_add_number == 0)))
        {
          /* Symbol OP symbol.  */
          resultP->X_op = op_left;
          resultP->X_op_symbol = right.X_add_symbol;
          if (op_left == O_add)
            resultP->X_add_number += right.X_add_number;
          else if (op_left == O_subtract)
            {
              resultP->X_add_number -= right.X_add_number;
              if (retval == rightseg && SEG_NORMAL (retval))
                {
                  retval = absolute_section;
                  rightseg = absolute_section;
                }
            }
        }
      else
        {
          /* The general case.  */
          resultP->X_add_symbol = make_expr_symbol (resultP);
          resultP->X_op_symbol = make_expr_symbol (&right);
          resultP->X_op = op_left;
          resultP->X_add_number = 0;
          resultP->X_unsigned = 1;
        }

      if (retval != rightseg)
        {
          if (! SEG_NORMAL (retval))
            {
              if (retval != undefined_section || SEG_NORMAL (rightseg))
                retval = rightseg;
            }
          else if (SEG_NORMAL (rightseg)
#ifdef DIFF_EXPR_OK
                   && op_left != O_subtract
#endif
                   )
            as_bad (_("operation combines symbols in different segments"));
        }

      op_left = op_right;
    }                           /* While next operator is >= this rank.  */

  /* The PA port needs this information.  */
  if (resultP->X_add_symbol)
    symbol_mark_used (resultP->X_add_symbol);

  return resultP->X_op == O_constant ? absolute_section : retval;
}
\f
/* This lives here because it belongs equally in expr.c & read.c.
   expr.c is just a branch office read.c anyway, and putting it
   here lessens the crowd at read.c.

   Assume input_line_pointer is at start of symbol name.
   Advance input_line_pointer past symbol name.
   Turn that character into a '\0', returning its former value.
   This allows a string compare (RMS wants symbol names to be strings)
   of the symbol name.
   There will always be a char following symbol name, because all good
   lines end in end-of-line.  */

char
get_symbol_end ()
{
  char c;

  /* We accept \001 in a name in case this is being called with a
     constructed string.  */
  if (is_name_beginner (c = *input_line_pointer++) || c == '\001')
    {
      while (is_part_of_name (c = *input_line_pointer++)
             || c == '\001')
        ;
      if (is_name_ender (c))
        c = *input_line_pointer++;
    }
  *--input_line_pointer = 0;
  return (c);
}

unsigned int
get_single_number ()
{
  expressionS exp;
  operand (&exp);
  return exp.X_add_number;
}