expr.c

/* expr.c -- arithmetic expression evaluation. */

/* Copyright (C) 1990-2015 Free Software Foundation, Inc.

   This file is part of GNU Bash, the Bourne Again SHell.

   Bash 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 3 of the License, or
   (at your option) any later version.

   Bash 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 Bash.  If not, see <http://www.gnu.org/licenses/>.
*/

/*
 All arithmetic is done as intmax_t integers with no checking for overflow
 (though division by 0 is caught and flagged as an error).

 The following operators are handled, grouped into a set of levels in
 order of decreasing precedence.

	"id++", "id--"		[post-increment and post-decrement]
	"++id", "--id"		[pre-increment and pre-decrement]
	"-", "+"		[(unary operators)]
	"!", "~"
	"**"			[(exponentiation)]
	"*", "/", "%"
	"+", "-"
	"<<", ">>"
	"<=", ">=", "<", ">"
	"==", "!="
	"&"
	"^"
	"|"
	"&&"
	"||"
	"expr ? expr : expr"
	"=", "*=", "/=", "%=", "+=", "-=", "<<=", ">>=", "&=", "^=", "|="
	,			[comma]

 (Note that most of these operators have special meaning to bash, and an
 entire expression should be quoted, e.g. "a=$a+1" or "a=a+1" to ensure
 that it is passed intact to the evaluator when using `let'.  When using
 the $[] or $(( )) forms, the text between the `[' and `]' or `((' and `))'
 is treated as if in double quotes.)

 Sub-expressions within parentheses have a precedence level greater than
 all of the above levels and are evaluated first.  Within a single prece-
 dence group, evaluation is left-to-right, except for the arithmetic
 assignment operator (`='), which is evaluated right-to-left (as in C).

 The expression evaluator returns the value of the expression (assignment
 statements have as a value what is returned by the RHS).  The `let'
 builtin, on the other hand, returns 0 if the last expression evaluates to
 a non-zero, and 1 otherwise.

 Implementation is a recursive-descent parser.

 Chet Ramey
 chet@po.cwru.edu
*/

#include "config.h"

#include <stdio.h>
#include "bashansi.h"

#if defined (HAVE_UNISTD_H)
#  ifdef _MINIX
#    include <sys/types.h>
#  endif
#  include <unistd.h>
#endif

#include "chartypes.h"
#include "bashintl.h"

#include "shell.h"
#include "typemax.h"		/* INTMAX_MAX, INTMAX_MIN */

/* Because of the $((...)) construct, expressions may include newlines.
   Here is a macro which accepts newlines, tabs and spaces as whitespace. */
#define cr_whitespace(c) (whitespace(c) || ((c) == '\n'))

/* Size be which the expression stack grows when necessary. */
#define EXPR_STACK_GROW_SIZE 10

/* Maximum amount of recursion allowed.  This prevents a non-integer
   variable such as "num=num+2" from infinitely adding to itself when
   "let num=num+2" is given. */
#define MAX_EXPR_RECURSION_LEVEL 1024

/* The Tokens.  Singing "The Lion Sleeps Tonight". */

#define EQEQ	1	/* "==" */
#define NEQ	2	/* "!=" */
#define LEQ	3	/* "<=" */
#define GEQ	4	/* ">=" */
#define STR	5	/* string */
#define NUM	6	/* number */
#define LAND	7	/* "&&" Logical AND */
#define LOR	8	/* "||" Logical OR */
#define LSH	9	/* "<<" Left SHift */
#define RSH    10	/* ">>" Right SHift */
#define OP_ASSIGN 11	/* op= expassign as in Posix.2 */
#define COND	12	/* exp1 ? exp2 : exp3 */
#define POWER	13	/* exp1**exp2 */
#define PREINC	14	/* ++var */
#define PREDEC	15	/* --var */
#define POSTINC	16	/* var++ */
#define POSTDEC	17	/* var-- */
#define EQ	'='
#define GT	'>'
#define LT	'<'
#define PLUS	'+'
#define MINUS	'-'
#define MUL	'*'
#define DIV	'/'
#define MOD	'%'
#define NOT	'!'
#define LPAR	'('
#define RPAR	')'
#define BAND	'&'	/* Bitwise AND */
#define BOR	'|'	/* Bitwise OR. */
#define BXOR	'^'	/* Bitwise eXclusive OR. */
#define BNOT	'~'	/* Bitwise NOT; Two's complement. */
#define QUES	'?'
#define COL	':'
#define COMMA	','

/* This should be the function corresponding to the operator with the
   highest precedence. */
#define EXP_HIGHEST	expcomma

#ifndef MAX_INT_LEN
#  define MAX_INT_LEN 32
#endif

struct lvalue
{
  char *tokstr;		/* possibly-rewritten lvalue if not NULL */
  intmax_t tokval;	/* expression evaluated value */
  SHELL_VAR *tokvar;	/* variable described by array or var reference */
  intmax_t ind;		/* array index if not -1 */
};

/* A structure defining a single expression context. */
typedef struct {
  int curtok, lasttok;
  char *expression, *tp, *lasttp;
  intmax_t tokval;
  char *tokstr;
  int noeval;
  struct lvalue lval;
} EXPR_CONTEXT;

static char	*expression;	/* The current expression */
static char	*tp;		/* token lexical position */
static char	*lasttp;	/* pointer to last token position */
static int	curtok;		/* the current token */
static int	lasttok;	/* the previous token */
static int	assigntok;	/* the OP in OP= */
static char	*tokstr;	/* current token string */
static intmax_t	tokval;		/* current token value */
static int	noeval;		/* set to 1 if no assignment to be done */
static procenv_t evalbuf;

static struct lvalue curlval = {0, 0, 0, -1};
static struct lvalue lastlval = {0, 0, 0, -1};

static int	_is_arithop __P((int));
static void	readtok __P((void));	/* lexical analyzer */

static void	init_lvalue __P((struct lvalue *));
static struct lvalue *alloc_lvalue __P((void));
static void	free_lvalue __P((struct lvalue *));

static intmax_t	expr_streval __P((char *, int, struct lvalue *));
static intmax_t	strlong __P((char *));
static void	evalerror __P((const char *));

static void	pushexp __P((void));
static void	popexp __P((void));
static void	expr_unwind __P((void));
static void	expr_bind_variable __P((char *, char *));
#if defined (ARRAY_VARS)
static void	expr_bind_array_element __P((char *, arrayind_t, char *));
#endif

static intmax_t subexpr __P((char *));

static intmax_t	expcomma __P((void));
static intmax_t expassign __P((void));
static intmax_t	expcond __P((void));
static intmax_t explor __P((void));
static intmax_t expland __P((void));
static intmax_t	expbor __P((void));
static intmax_t	expbxor __P((void));
static intmax_t	expband __P((void));
static intmax_t exp5 __P((void));
static intmax_t exp4 __P((void));
static intmax_t expshift __P((void));
static intmax_t exp3 __P((void));
static intmax_t exp2 __P((void));
static intmax_t	exppower __P((void));
static intmax_t exp1 __P((void));
static intmax_t exp0 __P((void));

/* Global var which contains the stack of expression contexts. */
static EXPR_CONTEXT **expr_stack;
static int expr_depth;		   /* Location in the stack. */
static int expr_stack_size;	   /* Number of slots already allocated. */

extern char *this_command_name;
extern int unbound_vars_is_error, last_command_exit_value;

#if defined (ARRAY_VARS)
extern const char * const bash_badsub_errmsg;
#endif

#define SAVETOK(X) \
  do { \
    (X)->curtok = curtok; \
    (X)->lasttok = lasttok; \
    (X)->tp = tp; \
    (X)->lasttp = lasttp; \
    (X)->tokval = tokval; \
    (X)->tokstr = tokstr; \
    (X)->noeval = noeval; \
    (X)->lval = curlval; \
  } while (0)

#define RESTORETOK(X) \
  do { \
    curtok = (X)->curtok; \
    lasttok = (X)->lasttok; \
    tp = (X)->tp; \
    lasttp = (X)->lasttp; \
    tokval = (X)->tokval; \
    tokstr = (X)->tokstr; \
    noeval = (X)->noeval; \
    curlval = (X)->lval; \
  } while (0)

/* Push and save away the contents of the globals describing the
   current expression context. */
static void
pushexp ()
{
  EXPR_CONTEXT *context;

  if (expr_depth >= MAX_EXPR_RECURSION_LEVEL)
    evalerror (_("expression recursion level exceeded"));

  if (expr_depth >= expr_stack_size)
    {
      expr_stack_size += EXPR_STACK_GROW_SIZE;
      expr_stack = (EXPR_CONTEXT **)xrealloc (expr_stack, expr_stack_size * sizeof (EXPR_CONTEXT *));
    }

  context = (EXPR_CONTEXT *)xmalloc (sizeof (EXPR_CONTEXT));

  context->expression = expression;
  SAVETOK(context);

  expr_stack[expr_depth++] = context;
}

/* Pop the the contents of the expression context stack into the
   globals describing the current expression context. */
static void
popexp ()
{
  EXPR_CONTEXT *context;

  if (expr_depth == 0)
    evalerror (_("recursion stack underflow"));

  context = expr_stack[--expr_depth];

  expression = context->expression;
  RESTORETOK (context);

  free (context);
}

static void
expr_unwind ()
{
  while (--expr_depth > 0)
    {
      if (expr_stack[expr_depth]->tokstr)
	free (expr_stack[expr_depth]->tokstr);

      if (expr_stack[expr_depth]->expression)
	free (expr_stack[expr_depth]->expression);

      free (expr_stack[expr_depth]);
    }
  free (expr_stack[expr_depth]);	/* free the allocated EXPR_CONTEXT */

  noeval = 0;	/* XXX */
}

static void
expr_bind_variable (lhs, rhs)
     char *lhs, *rhs;
{
  SHELL_VAR *v;

  v = bind_int_variable (lhs, rhs);
  if (v && (readonly_p (v) || noassign_p (v)))
    sh_longjmp (evalbuf, 1);	/* variable assignment error */
  stupidly_hack_special_variables (lhs);
}

#if defined (ARRAY_VARS)
/* Rewrite tok, which is of the form vname[expression], to vname[ind], where
   IND is the already-calculated value of expression. */
static void
expr_bind_array_element (tok, ind, rhs)
     char *tok;
     arrayind_t ind;
     char *rhs;
{
  char *lhs, *vname;
  size_t llen;
  char ibuf[INT_STRLEN_BOUND (arrayind_t) + 1], *istr;

  istr = fmtumax (ind, 10, ibuf, sizeof (ibuf), 0);
  vname = array_variable_name (tok, (char **)NULL, (int *)NULL);

  llen = strlen (vname) + sizeof (ibuf) + 3;
  lhs = xmalloc (llen);

  sprintf (lhs, "%s[%s]", vname, istr);		/* XXX */
  
/*itrace("expr_bind_array_element: %s=%s", lhs, rhs);*/
  expr_bind_variable (lhs, rhs);
  free (vname);
  free (lhs);
}
#endif /* ARRAY_VARS */

/* Evaluate EXPR, and return the arithmetic result.  If VALIDP is
   non-null, a zero is stored into the location to which it points
   if the expression is invalid, non-zero otherwise.  If a non-zero
   value is returned in *VALIDP, the return value of evalexp() may
   be used.

   The `while' loop after the longjmp is caught relies on the above
   implementation of pushexp and popexp leaving in expr_stack[0] the
   values that the variables had when the program started.  That is,
   the first things saved are the initial values of the variables that
   were assigned at program startup or by the compiler.  Therefore, it is
   safe to let the loop terminate when expr_depth == 0, without freeing up
   any of the expr_depth[0] stuff. */
intmax_t
evalexp (expr, validp)
     char *expr;
     int *validp;
{
  intmax_t val;
  int c;
  procenv_t oevalbuf;

  val = 0;
  noeval = 0;

  FASTCOPY (evalbuf, oevalbuf, sizeof (evalbuf));

  c = setjmp_nosigs (evalbuf);

  if (c)
    {
      FREE (tokstr);
      FREE (expression);
      tokstr = expression = (char *)NULL;

      expr_unwind ();

      if (validp)
	*validp = 0;
      return (0);
    }

  val = subexpr (expr);

  if (validp)
    *validp = 1;

  FASTCOPY (oevalbuf, evalbuf, sizeof (evalbuf));

  return (val);
}

static intmax_t
subexpr (expr)
     char *expr;
{
  intmax_t val;
  char *p;

  for (p = expr; p && *p && cr_whitespace (*p); p++)
    ;

  if (p == NULL || *p == '\0')
    return (0);

  pushexp ();
  expression = savestring (expr);
  tp = expression;

  curtok = lasttok = 0;
  tokstr = (char *)NULL;
  tokval = 0;
  init_lvalue (&curlval);
  lastlval = curlval;

  readtok ();

  val = EXP_HIGHEST ();

  if (curtok != 0)
    evalerror (_("syntax error in expression"));

  FREE (tokstr);
  FREE (expression);

  popexp ();

  return val;
}

static intmax_t
expcomma ()
{
  register intmax_t value;

  value = expassign ();
  while (curtok == COMMA)
    {
      readtok ();
      value = expassign ();
    }

  return value;
}
  
static intmax_t
expassign ()
{
  register intmax_t value;
  char *lhs, *rhs;
  arrayind_t lind;
#if defined (HAVE_IMAXDIV)
  imaxdiv_t idiv;
#endif

  value = expcond ();
  if (curtok == EQ || curtok == OP_ASSIGN)
    {
      int special, op;
      intmax_t lvalue;

      special = curtok == OP_ASSIGN;

      if (lasttok != STR)
	evalerror (_("attempted assignment to non-variable"));

      if (special)
	{
	  op = assigntok;		/* a OP= b */
	  lvalue = value;
	}

      /* XXX - watch out for pointer aliasing issues here */
      lhs = savestring (tokstr);
      /* save ind in case rhs is string var and evaluation overwrites it */
      lind = curlval.ind;
      readtok ();
      value = expassign ();

      if (special)
	{
	  if ((op == DIV || op == MOD) && value == 0)
	    {
	      if (noeval == 0)
		evalerror (_("division by 0"));
	      else
	        value = 1;
	    }

	  switch (op)
	    {
	    case MUL:
	      lvalue *= value;
	      break;
	    case DIV:
	    case MOD:
	      if (lvalue == INTMAX_MIN && value == -1)
		lvalue = (op == DIV) ? INTMAX_MIN : 0;
	      else
#if HAVE_IMAXDIV
		{
		  idiv = imaxdiv (lvalue, value);
		  lvalue = (op == DIV) ? idiv.quot : idiv.rem;
		}
#else
	        lvalue = (op == DIV) ? lvalue / value : lvalue % value;
#endif
	      break;
	    case PLUS:
	      lvalue += value;
	      break;
	    case MINUS:
	      lvalue -= value;
	      break;
	    case LSH:
	      lvalue <<= value;
	      break;
	    case RSH:
	      lvalue >>= value;
	      break;
	    case BAND:
	      lvalue &= value;
	      break;
	    case BOR:
	      lvalue |= value;
	      break;
	    case BXOR:
	      lvalue ^= value;
	      break;
	    default:
	      free (lhs);
	      evalerror (_("bug: bad expassign token"));
	      break;
	    }
	  value = lvalue;
	}

      rhs = itos (value);
      if (noeval == 0)
	{
#if defined (ARRAY_VARS)
	  if (lind != -1)
	    expr_bind_array_element (lhs, lind, rhs);
	  else
#endif
	    expr_bind_variable (lhs, rhs);
	}
      if (curlval.tokstr && curlval.tokstr == tokstr)
	init_lvalue (&curlval);

      free (rhs);
      free (lhs);
      FREE (tokstr);
      tokstr = (char *)NULL;		/* For freeing on errors. */
    }

  return (value);
}

/* Conditional expression (expr?expr:expr) */
static intmax_t
expcond ()
{
  intmax_t cval, val1, val2, rval;
  int set_noeval;

  set_noeval = 0;
  rval = cval = explor ();
  if (curtok == QUES)		/* found conditional expr */
    {
      if (cval == 0)
	{
	  set_noeval = 1;
	  noeval++;
	}

      readtok ();
      if (curtok == 0 || curtok == COL)
	evalerror (_("expression expected"));

      val1 = EXP_HIGHEST ();

      if (set_noeval)
	noeval--;
      if (curtok != COL)
	evalerror (_("`:' expected for conditional expression"));

      set_noeval = 0;
      if (cval)
 	{
 	  set_noeval = 1;
	  noeval++;
 	}

      readtok ();
      if (curtok == 0)
	evalerror (_("expression expected"));
      val2 = expcond ();

      if (set_noeval)
	noeval--;
      rval = cval ? val1 : val2;
      lasttok = COND;
    }
  return rval;
}

/* Logical OR. */
static intmax_t
explor ()
{
  register intmax_t val1, val2;
  int set_noeval;

  val1 = expland ();

  while (curtok == LOR)
    {
      set_noeval = 0;
      if (val1 != 0)
	{
	  noeval++;
	  set_noeval = 1;
	}
      readtok ();
      val2 = expland ();
      if (set_noeval)
	noeval--;
      val1 = val1 || val2;
      lasttok = LOR;
    }

  return (val1);
}

/* Logical AND. */
static intmax_t
expland ()
{
  register intmax_t val1, val2;
  int set_noeval;

  val1 = expbor ();

  while (curtok == LAND)
    {
      set_noeval = 0;
      if (val1 == 0)
	{
	  set_noeval = 1;
	  noeval++;
	}
      readtok ();
      val2 = expbor ();
      if (set_noeval)
	noeval--;
      val1 = val1 && val2;
      lasttok = LAND;
    }

  return (val1);
}

/* Bitwise OR. */
static intmax_t
expbor ()
{
  register intmax_t val1, val2;

  val1 = expbxor ();

  while (curtok == BOR)
    {
      readtok ();
      val2 = expbxor ();
      val1 = val1 | val2;
      lasttok = NUM;
    }

  return (val1);
}

/* Bitwise XOR. */
static intmax_t
expbxor ()
{
  register intmax_t val1, val2;

  val1 = expband ();

  while (curtok == BXOR)
    {
      readtok ();
      val2 = expband ();
      val1 = val1 ^ val2;
      lasttok = NUM;
    }

  return (val1);
}

/* Bitwise AND. */
static intmax_t
expband ()
{
  register intmax_t val1, val2;

  val1 = exp5 ();

  while (curtok == BAND)
    {
      readtok ();
      val2 = exp5 ();
      val1 = val1 & val2;
      lasttok = NUM;
    }

  return (val1);
}

static intmax_t
exp5 ()
{
  register intmax_t val1, val2;

  val1 = exp4 ();

  while ((curtok == EQEQ) || (curtok == NEQ))
    {
      int op = curtok;

      readtok ();
      val2 = exp4 ();
      if (op == EQEQ)
	val1 = (val1 == val2);
      else if (op == NEQ)
	val1 = (val1 != val2);
      lasttok = NUM;
    }
  return (val1);
}

static intmax_t
exp4 ()
{
  register intmax_t val1, val2;

  val1 = expshift ();
  while ((curtok == LEQ) ||
	 (curtok == GEQ) ||
	 (curtok == LT) ||
	 (curtok == GT))
    {
      int op = curtok;

      readtok ();
      val2 = expshift ();

      if (op == LEQ)
	val1 = val1 <= val2;
      else if (op == GEQ)
	val1 = val1 >= val2;
      else if (op == LT)
	val1 = val1 < val2;
      else			/* (op == GT) */
	val1 = val1 > val2;
      lasttok = NUM;
    }
  return (val1);
}

/* Left and right shifts. */
static intmax_t
expshift ()
{
  register intmax_t val1, val2;

  val1 = exp3 ();

  while ((curtok == LSH) || (curtok == RSH))
    {
      int op = curtok;

      readtok ();
      val2 = exp3 ();

      if (op == LSH)
	val1 = val1 << val2;
      else
	val1 = val1 >> val2;
      lasttok = NUM;
    }

  return (val1);
}

static intmax_t
exp3 ()
{
  register intmax_t val1, val2;

  val1 = exp2 ();

  while ((curtok == PLUS) || (curtok == MINUS))
    {
      int op = curtok;

      readtok ();
      val2 = exp2 ();

      if (op == PLUS)
	val1 += val2;
      else if (op == MINUS)
	val1 -= val2;
      lasttok = NUM;
    }
  return (val1);
}

static intmax_t
exp2 ()
{
  register intmax_t val1, val2;
#if defined (HAVE_IMAXDIV)
  imaxdiv_t idiv;
#endif

  val1 = exppower ();

  while ((curtok == MUL) ||
	 (curtok == DIV) ||
	 (curtok == MOD))
    {
      int op = curtok;
      char *stp, *sltp;

      stp = tp;
      readtok ();

      val2 = exppower ();

      /* Handle division by 0 and twos-complement arithmetic overflow */
      if (((op == DIV) || (op == MOD)) && (val2 == 0))
	{
	  if (noeval == 0)
	    {
	      sltp = lasttp;
	      lasttp = stp;
	      while (lasttp && *lasttp && whitespace (*lasttp))
		lasttp++;
	      evalerror (_("division by 0"));
	      lasttp = sltp;
	    }
	  else
	    val2 = 1;
	}
      else if (op == MOD && val1 == INTMAX_MIN && val2 == -1)
	{
	  val1 = 0;
	  continue;
	}
      else if (op == DIV && val1 == INTMAX_MIN && val2 == -1)
	val2 = 1;

      if (op == MUL)
	val1 *= val2;
      else if (op == DIV || op == MOD)
#if defined (HAVE_IMAXDIV)
	{
	  idiv = imaxdiv (val1, val2);
	  val1 = (op == DIV) ? idiv.quot : idiv.rem;
	}
#else
	val1 = (op == DIV) ? val1 / val2 : val1 % val2;
#endif
      lasttok = NUM;
    }
  return (val1);
}

static intmax_t
ipow (base, exp)
     intmax_t base, exp;
{
  intmax_t result;

  result = 1;
  while (exp)
    {
      if (exp & 1)
	result *= base;
      exp >>= 1;
      base *= base;
    }
  return result;
}

static intmax_t
exppower ()
{
  register intmax_t val1, val2, c;

  val1 = exp1 ();
  while (curtok == POWER)
    {
      readtok ();
      val2 = exppower ();	/* exponentiation is right-associative */
      lasttok = NUM;
      if (val2 == 0)
	return (1);
      if (val2 < 0)
	evalerror (_("exponent less than 0"));
      val1 = ipow (val1, val2);
    }
  return (val1);
}

static intmax_t
exp1 ()
{
  register intmax_t val;

  if (curtok == NOT)
    {
      readtok ();
      val = !exp1 ();
      lasttok = NUM;
    }
  else if (curtok == BNOT)
    {
      readtok ();
      val = ~exp1 ();
      lasttok = NUM;
    }
  else if (curtok == MINUS)
    {
      readtok ();
      val = - exp1 ();
      lasttok = NUM;
    }
  else if (curtok == PLUS)
    {
      readtok ();
      val = exp1 ();
      lasttok = NUM;
    }
  else
    val = exp0 ();

  return (val);
}

static intmax_t
exp0 ()
{
  register intmax_t val = 0, v2;
  char *vincdec;
  int stok;
  EXPR_CONTEXT ec;

  /* XXX - might need additional logic here to decide whether or not
	   pre-increment or pre-decrement is legal at this point. */
  if (curtok == PREINC || curtok == PREDEC)
    {
      stok = lasttok = curtok;
      readtok ();
      if (curtok != STR)
	/* readtok() catches this */
	evalerror (_("identifier expected after pre-increment or pre-decrement"));

      v2 = tokval + ((stok == PREINC) ? 1 : -1);
      vincdec = itos (v2);
      if (noeval == 0)
	{
#if defined (ARRAY_VARS)
	  if (curlval.ind != -1)
	    expr_bind_array_element (curlval.tokstr, curlval.ind, vincdec);
	  else
#endif
	    expr_bind_variable (tokstr, vincdec);
	}
      free (vincdec);
      val = v2;

      curtok = NUM;	/* make sure --x=7 is flagged as an error */
      readtok ();
    }
  else if (curtok == LPAR)
    {
      /* XXX - save curlval here?  Or entire expression context? */
      readtok ();
      val = EXP_HIGHEST ();

      if (curtok != RPAR) /* ( */
	evalerror (_("missing `)'"));

      /* Skip over closing paren. */
      readtok ();
    }
  else if ((curtok == NUM) || (curtok == STR))
    {
      val = tokval;
      if (curtok == STR)
	{
	  SAVETOK (&ec);
	  tokstr = (char *)NULL;	/* keep it from being freed */
          noeval = 1;
          readtok ();
          stok = curtok;

	  /* post-increment or post-decrement */
 	  if (stok == POSTINC || stok == POSTDEC)
 	    {
 	      /* restore certain portions of EC */
 	      tokstr = ec.tokstr;
 	      noeval = ec.noeval;
 	      curlval = ec.lval;
 	      lasttok = STR;	/* ec.curtok */

	      v2 = val + ((stok == POSTINC) ? 1 : -1);
	      vincdec = itos (v2);
	      if (noeval == 0)
		{
#if defined (ARRAY_VARS)
		  if (curlval.ind != -1)
		    expr_bind_array_element (curlval.tokstr, curlval.ind, vincdec);
		  else
#endif
		    expr_bind_variable (tokstr, vincdec);
		}
	      free (vincdec);
	      curtok = NUM;	/* make sure x++=7 is flagged as an error */
 	    }
 	  else
 	    {
	      /* XXX - watch out for pointer aliasing issues here */
	      if (stok == STR)	/* free new tokstr before old one is restored */
		FREE (tokstr);
	      RESTORETOK (&ec);
 	    }
	}
	  
      readtok ();
    }
  else
    evalerror (_("syntax error: operand expected"));

  return (val);
}

static void
init_lvalue (lv)
     struct lvalue *lv;
{
  lv->tokstr = 0;
  lv->tokvar = 0;
  lv->tokval = lv->ind = -1;
}

static struct lvalue *
alloc_lvalue ()
{
  struct lvalue *lv;

  lv = xmalloc (sizeof (struct lvalue));
  init_lvalue (lv);
  return (lv);
}

static void
free_lvalue (lv)
     struct lvalue *lv;
{
  free (lv);		/* should be inlined */
}

static intmax_t
expr_streval (tok, e, lvalue)
     char *tok;
     int e;
     struct lvalue *lvalue;
{
  SHELL_VAR *v;
  char *value;
  intmax_t tval;
#if defined (ARRAY_VARS)
  arrayind_t ind;
#endif

/*itrace("expr_streval: %s: noeval = %d", tok, noeval);*/
  /* If we are suppressing evaluation, just short-circuit here instead of
     going through the rest of the evaluator. */
  if (noeval)
    return (0);

  /* [[[[[ */
#if defined (ARRAY_VARS)
  v = (e == ']') ? array_variable_part (tok, (char **)0, (int *)0) : find_variable (tok);
#else
  v = find_variable (tok);
#endif

  if ((v == 0 || invisible_p (v)) && unbound_vars_is_error)
    {
#if defined (ARRAY_VARS)
      value = (e == ']') ? array_variable_name (tok, (char **)0, (int *)0) : tok;
#else
      value = tok;
#endif

      last_command_exit_value = EXECUTION_FAILURE;
      err_unboundvar (value);

#if defined (ARRAY_VARS)
      if (e == ']')
	FREE (value);	/* array_variable_name returns new memory */
#endif

      if (no_longjmp_on_fatal_error && interactive_shell)
	sh_longjmp (evalbuf, 1);

      if (interactive_shell)
	{
	  expr_unwind ();
	  top_level_cleanup ();
	  jump_to_top_level (DISCARD);
	}
      else
	jump_to_top_level (FORCE_EOF);
    }

#if defined (ARRAY_VARS)
  ind = -1;
  /* Second argument of 0 to get_array_value means that we don't allow
     references like array[@].  In this case, get_array_value is just
     like get_variable_value in that it does not return newly-allocated
     memory or quote the results. */
  value = (e == ']') ? get_array_value (tok, 0, (int *)NULL, &ind) : get_variable_value (v);
#else
  value = get_variable_value (v);
#endif

  tval = (value && *value) ? subexpr (value) : 0;

  if (lvalue)
    {
      lvalue->tokstr = tok;	/* XXX */
      lvalue->tokval = tval;
      lvalue->tokvar = v;	/* XXX */
#if defined (ARRAY_VARS)
      lvalue->ind = ind;
#else
      lvalue->ind = -1;
#endif
    }
	  
  return (tval);
}

static int
_is_multiop (c)
     int c;
{
  switch (c)
    {
    case EQEQ:
    case NEQ:
    case LEQ:
    case GEQ:
    case LAND:
    case LOR:
    case LSH:
    case RSH:
    case OP_ASSIGN:
    case COND:
    case POWER:
    case PREINC:
    case PREDEC:
    case POSTINC:
    case POSTDEC:
      return 1;
    default:
      return 0;
    }
}

static int
_is_arithop (c)
     int c;
{
  switch (c)
    {
    case EQ:
    case GT:
    case LT:
    case PLUS:
    case MINUS:
    case MUL:
    case DIV:
    case MOD:
    case NOT:
    case LPAR:
    case RPAR:
    case BAND:
    case BOR:
    case BXOR:
    case BNOT:
      return 1;		/* operator tokens */
    case QUES:
    case COL:
    case COMMA:
      return 1;		/* questionable */
    default:
      return 0;		/* anything else is invalid */
    }
}

/* Lexical analyzer/token reader for the expression evaluator.  Reads the
   next token and puts its value into curtok, while advancing past it.
   Updates value of tp.  May also set tokval (for number) or tokstr (for
   string). */
static void
readtok ()
{
  register char *cp, *xp;
  register unsigned char c, c1;
  register int e;
  struct lvalue lval;

  /* Skip leading whitespace. */
  cp = tp;
  c = e = 0;
  while (cp && (c = *cp) && (cr_whitespace (c)))
    cp++;

  if (c)
    cp++;

  if (c == '\0')
    {
      lasttok = curtok;
      curtok = 0;
      tp = cp;
      return;
    }
  lasttp = tp = cp - 1;

  if (legal_variable_starter (c))
    {
      /* variable names not preceded with a dollar sign are shell variables. */
      char *savecp;
      EXPR_CONTEXT ec;
      int peektok;

      while (legal_variable_char (c))
	c = *cp++;

      c = *--cp;

#if defined (ARRAY_VARS)
      if (c == '[')
	{
	  e = skipsubscript (cp, 0, 0);
	  if (cp[e] == ']')
	    {
	      cp += e + 1;
	      c = *cp;
	      e = ']';
	    }
	  else
	    evalerror (bash_badsub_errmsg);
	}
#endif /* ARRAY_VARS */

      *cp = '\0';
      /* XXX - watch out for pointer aliasing issues here */
      if (curlval.tokstr && curlval.tokstr == tokstr)
	init_lvalue (&curlval);

      FREE (tokstr);
      tokstr = savestring (tp);
      *cp = c;

      /* XXX - make peektok part of saved token state? */
      SAVETOK (&ec);
      tokstr = (char *)NULL;	/* keep it from being freed */
      tp = savecp = cp;
      noeval = 1;
      curtok = STR;
      readtok ();
      peektok = curtok;
      if (peektok == STR)	/* free new tokstr before old one is restored */
	FREE (tokstr);
      RESTORETOK (&ec);
      cp = savecp;

      /* The tests for PREINC and PREDEC aren't strictly correct, but they
	 preserve old behavior if a construct like --x=9 is given. */
      if (lasttok == PREINC || lasttok == PREDEC || peektok != EQ)
        {
          lastlval = curlval;
	  tokval = expr_streval (tokstr, e, &curlval);
        }
      else
	tokval = 0;

      lasttok = curtok;
      curtok = STR;
    }
  else if (DIGIT(c))
    {
      while (ISALNUM (c) || c == '#' || c == '@' || c == '_')
	c = *cp++;

      c = *--cp;
      *cp = '\0';

      tokval = strlong (tp);
      *cp = c;
      lasttok = curtok;
      curtok = NUM;
    }
  else
    {
      c1 = *cp++;
      if ((c == EQ) && (c1 == EQ))
	c = EQEQ;
      else if ((c == NOT) && (c1 == EQ))
	c = NEQ;
      else if ((c == GT) && (c1 == EQ))
	c = GEQ;
      else if ((c == LT) && (c1 == EQ))
	c = LEQ;
      else if ((c == LT) && (c1 == LT))
	{
	  if (*cp == '=')	/* a <<= b */
	    {
	      assigntok = LSH;
	      c = OP_ASSIGN;
	      cp++;
	    }
	  else
	    c = LSH;
	}
      else if ((c == GT) && (c1 == GT))
	{
	  if (*cp == '=')
	    {
	      assigntok = RSH;	/* a >>= b */
	      c = OP_ASSIGN;
	      cp++;
	    }
	  else
	    c = RSH;
	}
      else if ((c == BAND) && (c1 == BAND))
	c = LAND;
      else if ((c == BOR) && (c1 == BOR))
	c = LOR;
      else if ((c == '*') && (c1 == '*'))
	c = POWER;
      else if ((c == '-' || c == '+') && c1 == c && curtok == STR)
	c = (c == '-') ? POSTDEC : POSTINC;
      else if ((c == '-' || c == '+') && c1 == c)
	{
	  /* Quickly scan forward to see if this is followed by optional
	     whitespace and an identifier. */
	  xp = cp;
	  while (xp && *xp && cr_whitespace (*xp))
	    xp++;
	  if (legal_variable_starter ((unsigned char)*xp))
	    c = (c == '-') ? PREDEC : PREINC;
	  else
	    cp--;	/* not preinc or predec, so unget the character */
	}
      else if (c1 == EQ && member (c, "*/%+-&^|"))
	{
	  assigntok = c;	/* a OP= b */
	  c = OP_ASSIGN;
	}
      else if (_is_arithop (c) == 0)
	{
	  cp--;
	  /* use curtok, since it hasn't been copied to lasttok yet */
	  if (curtok == 0 || _is_arithop (curtok) || _is_multiop (curtok))
	    evalerror (_("syntax error: operand expected"));
	  else
	    evalerror (_("syntax error: invalid arithmetic operator"));
	}
      else
	cp--;			/* `unget' the character */

      /* Should check here to make sure that the current character is one
	 of the recognized operators and flag an error if not.  Could create
	 a character map the first time through and check it on subsequent
	 calls. */
      lasttok = curtok;
      curtok = c;
    }
  tp = cp;
}

static void
evalerror (msg)
     const char *msg;
{
  char *name, *t;

  name = this_command_name;
  for (t = expression; whitespace (*t); t++)
    ;
  internal_error (_("%s%s%s: %s (error token is \"%s\")"),
		   name ? name : "", name ? ": " : "", t,
		   msg, (lasttp && *lasttp) ? lasttp : "");
  sh_longjmp (evalbuf, 1);
}

/* Convert a string to an intmax_t integer, with an arbitrary base.
   0nnn -> base 8
   0[Xx]nn -> base 16
   Anything else: [base#]number (this is implemented to match ksh93)

   Base may be >=2 and <=64.  If base is <= 36, the numbers are drawn
   from [0-9][a-zA-Z], and lowercase and uppercase letters may be used
   interchangably.  If base is > 36 and <= 64, the numbers are drawn
   from [0-9][a-z][A-Z]_@ (a = 10, z = 35, A = 36, Z = 61, @ = 62, _ = 63 --
   you get the picture). */

static intmax_t
strlong (num)
     char *num;
{
  register char *s;
  register unsigned char c;
  int base, foundbase;
  intmax_t val;

  s = num;

  base = 10;
  foundbase = 0;
  if (*s == '0')
    {
      s++;

      if (*s == '\0')
	return 0;

       /* Base 16? */
      if (*s == 'x' || *s == 'X')
	{
	  base = 16;
	  s++;
	}
      else
	base = 8;
      foundbase++;
    }

  val = 0;
  for (c = *s++; c; c = *s++)
    {
      if (c == '#')
	{
	  if (foundbase)
	    evalerror (_("invalid number"));

	  /* Illegal base specifications raise an evaluation error. */
	  if (val < 2 || val > 64)
	    evalerror (_("invalid arithmetic base"));

	  base = val;
	  val = 0;
	  foundbase++;
	}
      else if (ISALNUM(c) || (c == '_') || (c == '@'))
	{
	  if (DIGIT(c))
	    c = TODIGIT(c);
	  else if (c >= 'a' && c <= 'z')
	    c -= 'a' - 10;
	  else if (c >= 'A' && c <= 'Z')
	    c -= 'A' - ((base <= 36) ? 10 : 36);
	  else if (c == '@')
	    c = 62;
	  else if (c == '_')
	    c = 63;

	  if (c >= base)
	    evalerror (_("value too great for base"));

	  val = (val * base) + c;
	}
      else
	break;
    }

  return (val);
}

#if defined (EXPR_TEST)
void *
xmalloc (n)
     int n;
{
  return (malloc (n));
}

void *
xrealloc (s, n)
     char *s;
     int n;
{
  return (realloc (s, n));
}

SHELL_VAR *find_variable () { return 0;}
SHELL_VAR *bind_variable () { return 0; }

char *get_string_value () { return 0; }

procenv_t top_level;

main (argc, argv)
     int argc;
     char **argv;
{
  register int i;
  intmax_t v;
  int expok;

  if (setjmp (top_level))
    exit (0);

  for (i = 1; i < argc; i++)
    {
      v = evalexp (argv[i], &expok);
      if (expok == 0)
	fprintf (stderr, _("%s: expression error\n"), argv[i]);
      else
	printf ("'%s' -> %ld\n", argv[i], v);
    }
  exit (0);
}

int
builtin_error (format, arg1, arg2, arg3, arg4, arg5)
     char *format;
{
  fprintf (stderr, "expr: ");
  fprintf (stderr, format, arg1, arg2, arg3, arg4, arg5);
  fprintf (stderr, "\n");
  return 0;
}

char *
itos (n)
     intmax_t n;
{
  return ("42");
}

#endif /* EXPR_TEST */