expr.c - busybox - Git at Google

 /* vi: set sw=4 ts=4: */
 /*
  * Mini expr implementation for busybox
  *
  * based on GNU expr Mike Parker.
  * Copyright (C) 86, 1991-1997, 1999 Free Software Foundation, Inc.
  *
  * Busybox modifications
  * Copyright (c) 2000  Edward Betts <edward@debian.org>.
  *
  * this program is free software; you can redistribute it and/or modify
  * it under the terms of the gnu general public license as published by
  * the free software foundation; either version 2 of the license, or
  * (at your option) any later version.
  *
  * this program is distributed in the hope that it will be useful,
  * but without any warranty; without even the implied warranty of
  * merchantability or fitness for a particular purpose. see the gnu
  * general public license for more details.
  *
  * you should have received a copy of the gnu general public license
  * along with this program; if not, write to the free software
  * foundation, inc., 59 temple place, suite 330, boston, ma 02111-1307 usa
  *
  */

 /* This program evaluates expressions.  Each token (operator, operand,
  * parenthesis) of the expression must be a seperate argument.  The
  * parser used is a reasonably general one, though any incarnation of
  * it is language-specific.  It is especially nice for expressions.
  *
  * No parse tree is needed; a new node is evaluated immediately.
  * One function can handle multiple operators all of equal precedence,
  * provided they all associate ((x op x) op x). */

 #include "busybox.h"
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <regex.h>
 #include <sys/types.h>


 /* The kinds of value we can have.  */
 enum valtype {
 	integer,
 	string
 };
 typedef enum valtype TYPE;

 /* A value is.... */
 struct valinfo {
 	TYPE type;			/* Which kind. */
 	union {				/* The value itself. */
 		int i;
 		char *s;
 	} u;
 };
 typedef struct valinfo VALUE;

 /* The arguments given to the program, minus the program name.  */
 static char **args;

 static VALUE *docolon (VALUE *sv, VALUE *pv);
 static VALUE *eval (void);
 static VALUE *int_value (int i);
 static VALUE *str_value (char *s);
 static int nextarg (char *str);
 static int null (VALUE *v);
 static int toarith (VALUE *v);
 static void freev (VALUE *v);
 static void tostring (VALUE *v);

 int expr_main (int argc, char **argv)
 {
 	VALUE *v;

 	if (argc == 1) {
 		error_msg_and_die("too few arguments\n");
 	}

 	args = argv + 1;

 	v = eval ();
 	if (*args)
 		error_msg_and_die ("syntax error\n");

 	if (v->type == integer)
 		printf ("%d\n", v->u.i);
 	else
 		printf ("%s\n", v->u.s);

 	exit (null (v));
 }

 /* Return a VALUE for I.  */

 static VALUE *int_value (int i)
 {
 	VALUE *v;

 	v = xmalloc (sizeof(VALUE));
 	v->type = integer;
 	v->u.i = i;
 	return v;
 }

 /* Return a VALUE for S.  */

 static VALUE *str_value (char *s)
 {
 	VALUE *v;

 	v = xmalloc (sizeof(VALUE));
 	v->type = string;
 	v->u.s = strdup (s);
 	return v;
 }

 /* Free VALUE V, including structure components.  */

 static void freev (VALUE *v)
 {
 	if (v->type == string)
 		free (v->u.s);
 	free (v);
 }

 /* Return nonzero if V is a null-string or zero-number.  */

 static int null (VALUE *v)
 {
 	switch (v->type) {
 		case integer:
 			return v->u.i == 0;
 		case string:
 			return v->u.s[0] == '\0' || strcmp (v->u.s, "0") == 0;
 		default:
 			abort ();
 	}
 }

 /* Coerce V to a string value (can't fail).  */

 static void tostring (VALUE *v)
 {
 	char *temp;

 	if (v->type == integer) {
 		temp = xmalloc (4 * (sizeof (int) / sizeof (char)));
 		sprintf (temp, "%d", v->u.i);
 		v->u.s = temp;
 		v->type = string;
 	}
 }

 /* Coerce V to an integer value.  Return 1 on success, 0 on failure.  */

 static int toarith (VALUE *v)
 {
 	int i;

 	switch (v->type) {
 		case integer:
 			return 1;
 		case string:
 			i = 0;
 			/* Don't interpret the empty string as an integer.  */
 			if (v->u.s == 0)
 				return 0;
 			i = atoi(v->u.s);
 			free (v->u.s);
 			v->u.i = i;
 			v->type = integer;
 			return 1;
 		default:
 			abort ();
 	}
 }

 /* Return nonzero if the next token matches STR exactly.
    STR must not be NULL.  */

 static int
 nextarg (char *str)
 {
 	if (*args == NULL)
 		return 0;
 	return strcmp (*args, str) == 0;
 }

 /* The comparison operator handling functions.  */

 #define cmpf(name, rel)					\
 static int name (l, r) VALUE *l; VALUE *r;		\
 {							\
 	if (l->type == string || r->type == string) {		\
 		tostring (l);				\
 		tostring (r);				\
 		return strcmp (l->u.s, r->u.s) rel 0;	\
 	}						\
 	else						\
 		return l->u.i rel r->u.i;		\
 }
  cmpf (less_than, <)
  cmpf (less_equal, <=)
  cmpf (equal, ==)
  cmpf (not_equal, !=)
  cmpf (greater_equal, >=)
  cmpf (greater_than, >)

 #undef cmpf

 /* The arithmetic operator handling functions.  */

 #define arithf(name, op)			\
 static						\
 int name (l, r) VALUE *l; VALUE *r;		\
 {						\
   if (!toarith (l) || !toarith (r))		\
     error_msg_and_die ("non-numeric argument\n");	\
   return l->u.i op r->u.i;			\
 }

 #define arithdivf(name, op)			\
 int name (l, r) VALUE *l; VALUE *r;		\
 {						\
   if (!toarith (l) || !toarith (r))		\
     error_msg_and_die ( "non-numeric argument\n");	\
   if (r->u.i == 0)				\
     error_msg_and_die ( "division by zero\n");		\
   return l->u.i op r->u.i;			\
 }

  arithf (plus, +)
  arithf (minus, -)
  arithf (multiply, *)
  arithdivf (divide, /)
  arithdivf (mod, %)

 #undef arithf
 #undef arithdivf

 /* Do the : operator.
    SV is the VALUE for the lhs (the string),
    PV is the VALUE for the rhs (the pattern).  */

 static VALUE *docolon (VALUE *sv, VALUE *pv)
 {
 	VALUE *v;
 	const char *errmsg;
 	struct re_pattern_buffer re_buffer;
 	struct re_registers re_regs;
 	int len;

 	tostring (sv);
 	tostring (pv);

 	if (pv->u.s[0] == '^') {
 		fprintf (stderr, "\
 warning: unportable BRE: `%s': using `^' as the first character\n\
 of a basic regular expression is not portable; it is being ignored",
 		pv->u.s);
 	}

 	len = strlen (pv->u.s);
 	memset (&re_buffer, 0, sizeof (re_buffer));
 	memset (&re_regs, 0, sizeof (re_regs));
 	re_buffer.allocated = 2 * len;
 	re_buffer.buffer = (unsigned char *) xmalloc (re_buffer.allocated);
 	re_buffer.translate = 0;
 	re_syntax_options = RE_SYNTAX_POSIX_BASIC;
 	errmsg = re_compile_pattern (pv->u.s, len, &re_buffer);
 	if (errmsg) {
 		error_msg_and_die("%s\n", errmsg);
 	}

 	len = re_match (&re_buffer, sv->u.s, strlen (sv->u.s), 0, &re_regs);
 	if (len >= 0) {
 		/* Were \(...\) used? */
 		if (re_buffer.re_nsub > 0) { /* was (re_regs.start[1] >= 0) */
 			sv->u.s[re_regs.end[1]] = '\0';
 			v = str_value (sv->u.s + re_regs.start[1]);
 		}
 		else
 			v = int_value (len);
 	}
 	else {
 		/* Match failed -- return the right kind of null.  */
 		if (re_buffer.re_nsub > 0)
 			v = str_value ("");
 		else
 			v = int_value (0);
 	}
 	free (re_buffer.buffer);
 	return v;
 }

 /* Handle bare operands and ( expr ) syntax.  */

 static VALUE *eval7 (void)
 {
 	VALUE *v;

 	if (!*args)
 		error_msg_and_die ( "syntax error\n");

 	if (nextarg ("(")) {
 		args++;
 		v = eval ();
 		if (!nextarg (")"))
 			error_msg_and_die ( "syntax error\n");
 			args++;
 			return v;
 		}

 	if (nextarg (")"))
 		error_msg_and_die ( "syntax error\n");

 	return str_value (*args++);
 }

 /* Handle match, substr, index, length, and quote keywords.  */

 static VALUE *eval6 (void)
 {
 	VALUE *l, *r, *v, *i1, *i2;

 	if (nextarg ("quote")) {
 		args++;
 		if (!*args)
 			error_msg_and_die ( "syntax error\n");
 		return str_value (*args++);
 	}
 	else if (nextarg ("length")) {
 		args++;
 		r = eval6 ();
 		tostring (r);
 		v = int_value (strlen (r->u.s));
 		freev (r);
 		return v;
 	}
 	else if (nextarg ("match")) {
 		args++;
 		l = eval6 ();
 		r = eval6 ();
 		v = docolon (l, r);
 		freev (l);
 		freev (r);
 		return v;
 	}
 	else if (nextarg ("index")) {
 		args++;
 		l = eval6 ();
 		r = eval6 ();
 		tostring (l);
 		tostring (r);
 		v = int_value (strcspn (l->u.s, r->u.s) + 1);
 		if (v->u.i == (int) strlen (l->u.s) + 1)
 			v->u.i = 0;
 		freev (l);
 		freev (r);
 		return v;
 	}
 	else if (nextarg ("substr")) {
 		args++;
 		l = eval6 ();
 		i1 = eval6 ();
 		i2 = eval6 ();
 		tostring (l);
 		if (!toarith (i1) || !toarith (i2)
 			|| i1->u.i > (int) strlen (l->u.s)
 			|| i1->u.i <= 0 || i2->u.i <= 0)
 		v = str_value ("");
 		else {
 			v = xmalloc (sizeof(VALUE));
 			v->type = string;
 			v->u.s = strncpy ((char *) xmalloc (i2->u.i + 1),
 				l->u.s + i1->u.i - 1, i2->u.i);
 				v->u.s[i2->u.i] = 0;
 		}
 		freev (l);
 		freev (i1);
 		freev (i2);
 		return v;
 	}
 	else
 		return eval7 ();
 }

 /* Handle : operator (pattern matching).
    Calls docolon to do the real work.  */

 static VALUE *eval5 (void)
 {
 	VALUE *l, *r, *v;

 	l = eval6 ();
 	while (nextarg (":")) {
 		args++;
 		r = eval6 ();
 		v = docolon (l, r);
 		freev (l);
 		freev (r);
 		l = v;
 	}
 	return l;
 }

 /* Handle *, /, % operators.  */

 static VALUE *eval4 (void)
 {
 	VALUE *l, *r;
 	int (*fxn) (), val;

 	l = eval5 ();
 	while (1) {
 		if (nextarg ("*"))
 			fxn = multiply;
 		else if (nextarg ("/"))
 			fxn = divide;
 		else if (nextarg ("%"))
 			fxn = mod;
 		else
 			return l;
 		args++;
 		r = eval5 ();
 		val = (*fxn) (l, r);
 		freev (l);
 		freev (r);
 		l = int_value (val);
 	}
 }

 /* Handle +, - operators.  */

 static VALUE *eval3 (void)
 {
 	VALUE *l, *r;
 	int (*fxn) (), val;

 	l = eval4 ();
 	while (1) {
 		if (nextarg ("+"))
 			fxn = plus;
 		else if (nextarg ("-"))
 			fxn = minus;
 		else
 			return l;
 		args++;
 		r = eval4 ();
 		val = (*fxn) (l, r);
 		freev (l);
 		freev (r);
 		l = int_value (val);
 	}
 }

 /* Handle comparisons.  */

 static VALUE *eval2 (void)
 {
 	VALUE *l, *r;
 	int (*fxn) (), val;

 	l = eval3 ();
 	while (1) {
 		if (nextarg ("<"))
 			fxn = less_than;
 		else if (nextarg ("<="))
 			fxn = less_equal;
 		else if (nextarg ("=") || nextarg ("=="))
 			fxn = equal;
 		else if (nextarg ("!="))
 			fxn = not_equal;
 		else if (nextarg (">="))
 			fxn = greater_equal;
 		else if (nextarg (">"))
 			fxn = greater_than;
 		else
 			return l;
 		args++;
 		r = eval3 ();
 		toarith (l);
 		toarith (r);
 		val = (*fxn) (l, r);
 		freev (l);
 		freev (r);
 		l = int_value (val);
 	}
 }

 /* Handle &.  */

 static VALUE *eval1 (void)
 {
 	VALUE *l, *r;

 	l = eval2 ();
 	while (nextarg ("&")) {
 		args++;
 		r = eval2 ();
 		if (null (l) || null (r)) {
 			freev (l);
 			freev (r);
 			l = int_value (0);
 		}
 		else
 			freev (r);
 	}
 	return l;
 }

 /* Handle |.  */

 static VALUE *eval (void)
 {
 	VALUE *l, *r;

 	l = eval1 ();
 	while (nextarg ("|")) {
 		args++;
 		r = eval1 ();
 		if (null (l)) {
 			freev (l);
 			l = r;
 		}
 		else
 			freev (r);
 	}
 	return l;
 }
	/* vi: set sw=4 ts=4: */
	/*
	* Mini expr implementation for busybox
	*
	* based on GNU expr Mike Parker.
	* Copyright (C) 86, 1991-1997, 1999 Free Software Foundation, Inc.
	*
	* Busybox modifications
	* Copyright (c) 2000 Edward Betts <edward@debian.org>.
	*
	* this program is free software; you can redistribute it and/or modify
	* it under the terms of the gnu general public license as published by
	* the free software foundation; either version 2 of the license, or
	* (at your option) any later version.
	*
	* this program is distributed in the hope that it will be useful,
	* but without any warranty; without even the implied warranty of
	* merchantability or fitness for a particular purpose. see the gnu
	* general public license for more details.
	*
	* you should have received a copy of the gnu general public license
	* along with this program; if not, write to the free software
	* foundation, inc., 59 temple place, suite 330, boston, ma 02111-1307 usa
	*
	*/

	/* This program evaluates expressions. Each token (operator, operand,
	* parenthesis) of the expression must be a seperate argument. The
	* parser used is a reasonably general one, though any incarnation of
	* it is language-specific. It is especially nice for expressions.
	*
	* No parse tree is needed; a new node is evaluated immediately.
	* One function can handle multiple operators all of equal precedence,
	* provided they all associate ((x op x) op x). */

	#include "busybox.h"
	#include <stdio.h>
	#include <string.h>
	#include <stdlib.h>
	#include <regex.h>
	#include <sys/types.h>


	/* The kinds of value we can have. */
	enum valtype {
	integer,
	string
	};
	typedef enum valtype TYPE;

	/* A value is.... */
	struct valinfo {
	TYPE type; /* Which kind. */
	union { /* The value itself. */
	int i;
	char *s;
	} u;
	};
	typedef struct valinfo VALUE;

	/* The arguments given to the program, minus the program name. */
	static char **args;

	static VALUE docolon (VALUE sv, VALUE *pv);
	static VALUE *eval (void);
	static VALUE *int_value (int i);
	static VALUE str_value (char s);
	static int nextarg (char *str);
	static int null (VALUE *v);
	static int toarith (VALUE *v);
	static void freev (VALUE *v);
	static void tostring (VALUE *v);

	int expr_main (int argc, char **argv)
	{
	VALUE *v;

	if (argc == 1) {
	error_msg_and_die("too few arguments\n");
	}

	args = argv + 1;

	v = eval ();
	if (*args)
	error_msg_and_die ("syntax error\n");

	if (v->type == integer)
	printf ("%d\n", v->u.i);
	else
	printf ("%s\n", v->u.s);

	exit (null (v));
	}

	/* Return a VALUE for I. */

	static VALUE *int_value (int i)
	{
	VALUE *v;

	v = xmalloc (sizeof(VALUE));
	v->type = integer;
	v->u.i = i;
	return v;
	}

	/* Return a VALUE for S. */

	static VALUE str_value (char s)
	{
	VALUE *v;

	v = xmalloc (sizeof(VALUE));
	v->type = string;
	v->u.s = strdup (s);
	return v;
	}

	/* Free VALUE V, including structure components. */

	static void freev (VALUE *v)
	{
	if (v->type == string)
	free (v->u.s);
	free (v);
	}

	/* Return nonzero if V is a null-string or zero-number. */

	static int null (VALUE *v)
	{
	switch (v->type) {
	case integer:
	return v->u.i == 0;
	case string:
	return v->u.s[0] == '\0' \|\| strcmp (v->u.s, "0") == 0;
	default:
	abort ();
	}
	}

	/* Coerce V to a string value (can't fail). */

	static void tostring (VALUE *v)
	{
	char *temp;

	if (v->type == integer) {
	temp = xmalloc (4 * (sizeof (int) / sizeof (char)));
	sprintf (temp, "%d", v->u.i);
	v->u.s = temp;
	v->type = string;
	}
	}

	/* Coerce V to an integer value. Return 1 on success, 0 on failure. */

	static int toarith (VALUE *v)
	{
	int i;

	switch (v->type) {
	case integer:
	return 1;
	case string:
	i = 0;
	/* Don't interpret the empty string as an integer. */
	if (v->u.s == 0)
	return 0;
	i = atoi(v->u.s);
	free (v->u.s);
	v->u.i = i;
	v->type = integer;
	return 1;
	default:
	abort ();
	}
	}

	/* Return nonzero if the next token matches STR exactly.
	STR must not be NULL. */

	static int
	nextarg (char *str)
	{
	if (*args == NULL)
	return 0;
	return strcmp (*args, str) == 0;
	}

	/* The comparison operator handling functions. */

	#define cmpf(name, rel) \
	static int name (l, r) VALUE l; VALUE r; \
	{ \
	if (l->type == string \|\| r->type == string) { \
	tostring (l); \
	tostring (r); \
	return strcmp (l->u.s, r->u.s) rel 0; \
	} \
	else \
	return l->u.i rel r->u.i; \
	}
	cmpf (less_than, <)
	cmpf (less_equal, <=)
	cmpf (equal, ==)
	cmpf (not_equal, !=)
	cmpf (greater_equal, >=)
	cmpf (greater_than, >)

	#undef cmpf

	/* The arithmetic operator handling functions. */

	#define arithf(name, op) \
	static \
	int name (l, r) VALUE l; VALUE r; \
	{ \
	if (!toarith (l) \|\| !toarith (r)) \
	error_msg_and_die ("non-numeric argument\n"); \
	return l->u.i op r->u.i; \
	}

	#define arithdivf(name, op) \
	int name (l, r) VALUE l; VALUE r; \
	{ \
	if (!toarith (l) \|\| !toarith (r)) \
	error_msg_and_die ( "non-numeric argument\n"); \
	if (r->u.i == 0) \
	error_msg_and_die ( "division by zero\n"); \
	return l->u.i op r->u.i; \
	}

	arithf (plus, +)
	arithf (minus, -)
	arithf (multiply, *)
	arithdivf (divide, /)
	arithdivf (mod, %)

	#undef arithf
	#undef arithdivf

	/* Do the : operator.
	SV is the VALUE for the lhs (the string),
	PV is the VALUE for the rhs (the pattern). */

	static VALUE docolon (VALUE sv, VALUE *pv)
	{
	VALUE *v;
	const char *errmsg;
	struct re_pattern_buffer re_buffer;
	struct re_registers re_regs;
	int len;

	tostring (sv);
	tostring (pv);

	if (pv->u.s[0] == '^') {
	fprintf (stderr, "\
	warning: unportable BRE: `%s': using `^' as the first character\n\
	of a basic regular expression is not portable; it is being ignored",
	pv->u.s);
	}

	len = strlen (pv->u.s);
	memset (&re_buffer, 0, sizeof (re_buffer));
	memset (&re_regs, 0, sizeof (re_regs));
	re_buffer.allocated = 2 * len;
	re_buffer.buffer = (unsigned char *) xmalloc (re_buffer.allocated);
	re_buffer.translate = 0;
	re_syntax_options = RE_SYNTAX_POSIX_BASIC;
	errmsg = re_compile_pattern (pv->u.s, len, &re_buffer);
	if (errmsg) {
	error_msg_and_die("%s\n", errmsg);
	}

	len = re_match (&re_buffer, sv->u.s, strlen (sv->u.s), 0, &re_regs);
	if (len >= 0) {
	/* Were \(...\) used? */
	if (re_buffer.re_nsub > 0) { /* was (re_regs.start[1] >= 0) */
	sv->u.s[re_regs.end[1]] = '\0';
	v = str_value (sv->u.s + re_regs.start[1]);
	}
	else
	v = int_value (len);
	}
	else {
	/* Match failed -- return the right kind of null. */
	if (re_buffer.re_nsub > 0)
	v = str_value ("");
	else
	v = int_value (0);
	}
	free (re_buffer.buffer);
	return v;
	}

	/* Handle bare operands and ( expr ) syntax. */

	static VALUE *eval7 (void)
	{
	VALUE *v;

	if (!*args)
	error_msg_and_die ( "syntax error\n");

	if (nextarg ("(")) {
	args++;
	v = eval ();
	if (!nextarg (")"))
	error_msg_and_die ( "syntax error\n");
	args++;
	return v;
	}

	if (nextarg (")"))
	error_msg_and_die ( "syntax error\n");

	return str_value (*args++);
	}

	/* Handle match, substr, index, length, and quote keywords. */

	static VALUE *eval6 (void)
	{
	VALUE l, r, v, i1, *i2;

	if (nextarg ("quote")) {
	args++;
	if (!*args)
	error_msg_and_die ( "syntax error\n");
	return str_value (*args++);
	}
	else if (nextarg ("length")) {
	args++;
	r = eval6 ();
	tostring (r);
	v = int_value (strlen (r->u.s));
	freev (r);
	return v;
	}
	else if (nextarg ("match")) {
	args++;
	l = eval6 ();
	r = eval6 ();
	v = docolon (l, r);
	freev (l);
	freev (r);
	return v;
	}
	else if (nextarg ("index")) {
	args++;
	l = eval6 ();
	r = eval6 ();
	tostring (l);
	tostring (r);
	v = int_value (strcspn (l->u.s, r->u.s) + 1);
	if (v->u.i == (int) strlen (l->u.s) + 1)
	v->u.i = 0;
	freev (l);
	freev (r);
	return v;
	}
	else if (nextarg ("substr")) {
	args++;
	l = eval6 ();
	i1 = eval6 ();
	i2 = eval6 ();
	tostring (l);
	if (!toarith (i1) \|\| !toarith (i2)
	\|\| i1->u.i > (int) strlen (l->u.s)
	\|\| i1->u.i <= 0 \|\| i2->u.i <= 0)
	v = str_value ("");
	else {
	v = xmalloc (sizeof(VALUE));
	v->type = string;
	v->u.s = strncpy ((char *) xmalloc (i2->u.i + 1),
	l->u.s + i1->u.i - 1, i2->u.i);
	v->u.s[i2->u.i] = 0;
	}
	freev (l);
	freev (i1);
	freev (i2);
	return v;
	}
	else
	return eval7 ();
	}

	/* Handle : operator (pattern matching).
	Calls docolon to do the real work. */

	static VALUE *eval5 (void)
	{
	VALUE l, r, *v;

	l = eval6 ();
	while (nextarg (":")) {
	args++;
	r = eval6 ();
	v = docolon (l, r);
	freev (l);
	freev (r);
	l = v;
	}
	return l;
	}

	/* Handle , /, % operators. /

	static VALUE *eval4 (void)
	{
	VALUE l, r;
	int (*fxn) (), val;

	l = eval5 ();
	while (1) {
	if (nextarg ("*"))
	fxn = multiply;
	else if (nextarg ("/"))
	fxn = divide;
	else if (nextarg ("%"))
	fxn = mod;
	else
	return l;
	args++;
	r = eval5 ();
	val = (*fxn) (l, r);
	freev (l);
	freev (r);
	l = int_value (val);
	}
	}

	/* Handle +, - operators. */

	static VALUE *eval3 (void)
	{
	VALUE l, r;
	int (*fxn) (), val;

	l = eval4 ();
	while (1) {
	if (nextarg ("+"))
	fxn = plus;
	else if (nextarg ("-"))
	fxn = minus;
	else
	return l;
	args++;
	r = eval4 ();
	val = (*fxn) (l, r);
	freev (l);
	freev (r);
	l = int_value (val);
	}
	}

	/* Handle comparisons. */

	static VALUE *eval2 (void)
	{
	VALUE l, r;
	int (*fxn) (), val;

	l = eval3 ();
	while (1) {
	if (nextarg ("<"))
	fxn = less_than;
	else if (nextarg ("<="))
	fxn = less_equal;
	else if (nextarg ("=") \|\| nextarg ("=="))
	fxn = equal;
	else if (nextarg ("!="))
	fxn = not_equal;
	else if (nextarg (">="))
	fxn = greater_equal;
	else if (nextarg (">"))
	fxn = greater_than;
	else
	return l;
	args++;
	r = eval3 ();
	toarith (l);
	toarith (r);
	val = (*fxn) (l, r);
	freev (l);
	freev (r);
	l = int_value (val);
	}
	}

	/* Handle &. */

	static VALUE *eval1 (void)
	{
	VALUE l, r;

	l = eval2 ();
	while (nextarg ("&")) {
	args++;
	r = eval2 ();
	if (null (l) \|\| null (r)) {
	freev (l);
	freev (r);
	l = int_value (0);
	}
	else
	freev (r);
	}
	return l;
	}

	/* Handle \|. */

	static VALUE *eval (void)
	{
	VALUE l, r;

	l = eval1 ();
	while (nextarg ("\|")) {
	args++;
	r = eval1 ();
	if (null (l)) {
	freev (l);
	l = r;
	}
	else
	freev (r);
	}
	return l;
	}