xref: /csrg-svn/usr.bin/m4/expr.c (revision 69109)

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Ozan Yigit at York University.
 *
 * %sccs.include.redist.c%
 */

#ifndef lint
static char sccsid[] = "@(#)expr.c	8.2 (Berkeley) 04/29/95";
#endif /* not lint */

#include <sys/cdefs.h>
#include <stdio.h>

/*
 *      expression evaluator: performs a standard recursive
 *      descent parse to evaluate any expression permissible
 *      within the following grammar:
 *
 *      expr    :       query EOS
 *      query   :       lor
 *              |       lor "?" query ":" query
 *      lor     :       land { "||" land }
 *      land    :       not { "&&" not }
 *	not	:	eqrel
 *		|	'!' not
 *      eqrel   :       shift { eqrelop shift }
 *      shift   :       primary { shop primary }
 *      primary :       term { addop term }
 *      term    :       exp { mulop exp }
 *	exp	:	unary { expop unary }
 *      unary   :       factor
 *              |       unop unary
 *      factor  :       constant
 *              |       "(" query ")"
 *      constant:       num
 *              |       "'" CHAR "'"
 *      num     :       DIGIT
 *              |       DIGIT num
 *      shop    :       "<<"
 *              |       ">>"
 *      eqrel   :       "="
 *              |       "=="
 *              |       "!="
 *      	|       "<"
 *              |       ">"
 *              |       "<="
 *              |       ">="
 *
 *
 *      This expression evaluator is lifted from a public-domain
 *      C Pre-Processor included with the DECUS C Compiler distribution.
 *      It is hacked somewhat to be suitable for m4.
 *
 *      Originally by:  Mike Lutz
 *                      Bob Harper
 */

#define TRUE    1
#define FALSE   0
#define EOS     (char) 0
#define EQL     0
#define NEQ     1
#define LSS     2
#define LEQ     3
#define GTR     4
#define GEQ     5
#define OCTAL   8
#define DECIMAL 10

static char *nxtch;		       /* Parser scan pointer */

static int query __P((void));
static int lor __P((void));
static int land __P((void));
static int not __P((void));
static int eqrel __P((void));
static int shift __P((void));
static int primary __P((void));
static int term __P((void));
static int exp __P((void));
static int unary __P((void));
static int factor __P((void));
static int constant __P((void));
static int num __P((void));
static int geteqrel __P((void));
static int skipws __P((void));
static void experr __P((char *));

/*
 * For longjmp
 */
#include <setjmp.h>
static jmp_buf expjump;

/*
 * macros:
 *      ungetch - Put back the last character examined.
 *      getch   - return the next character from expr string.
 */
#define ungetch()       nxtch--
#define getch()         *nxtch++

int
expr(expbuf)
char *expbuf;
{
	register int rval;

	nxtch = expbuf;
	if (setjmp(expjump) != 0)
		return FALSE;

	rval = query();
	if (skipws() == EOS)
		return rval;

	printf("m4: ill-formed expression.\n");
	return FALSE;
}

/*
 * query : lor | lor '?' query ':' query
 */
static int
query()
{
	register int bool, true_val, false_val;

	bool = lor();
	if (skipws() != '?') {
		ungetch();
		return bool;
	}

	true_val = query();
	if (skipws() != ':')
		experr("bad query");

	false_val = query();
	return bool ? true_val : false_val;
}

/*
 * lor : land { '||' land }
 */
static int
lor()
{
	register int c, vl, vr;

	vl = land();
	while ((c = skipws()) == '|') {
		if (getch() != '|')
			ungetch();
		vr = land();
		vl = vl || vr;
	}

	ungetch();
	return vl;
}

/*
 * land : not { '&&' not }
 */
static int
land()
{
	register int c, vl, vr;

	vl = not();
	while ((c = skipws()) == '&') {
		if (getch() != '&')
			ungetch();
		vr = not();
		vl = vl && vr;
	}

	ungetch();
	return vl;
}

/*
 * not : eqrel | '!' not
 */
static int
not()
{
	register int val, c;

	if ((c = skipws()) == '!' && getch() != '=') {
		ungetch();
		val = not();
		return !val;
	}

	if (c == '!')
		ungetch();
	ungetch();
	return eqrel();
}

/*
 * eqrel : shift { eqrelop shift }
 */
static int
eqrel()
{
	register int vl, vr, eqrel;

	vl = shift();
	while ((eqrel = geteqrel()) != -1) {
		vr = shift();

		switch (eqrel) {

		case EQL:
			vl = (vl == vr);
			break;
		case NEQ:
			vl = (vl != vr);
			break;

		case LEQ:
			vl = (vl <= vr);
			break;
		case LSS:
			vl = (vl < vr);
			break;
		case GTR:
			vl = (vl > vr);
			break;
		case GEQ:
			vl = (vl >= vr);
			break;
		}
	}
	return vl;
}

/*
 * shift : primary { shop primary }
 */
static int
shift()
{
	register int vl, vr, c;

	vl = primary();
	while (((c = skipws()) == '<' || c == '>') && getch() == c) {
		vr = primary();

		if (c == '<')
			vl <<= vr;
		else
			vl >>= vr;
	}

	if (c == '<' || c == '>')
		ungetch();
	ungetch();
	return vl;
}

/*
 * primary : term { addop term }
 */
static int
primary()
{
	register int c, vl, vr;

	vl = term();
	while ((c = skipws()) == '+' || c == '-') {
		vr = term();

		if (c == '+')
			vl += vr;
		else
			vl -= vr;
	}

	ungetch();
	return vl;
}

/*
 * <term> := <exp> { <mulop> <exp> }
 */
static int
term()
{
	register int c, vl, vr;

	vl = exp();
	while ((c = skipws()) == '*' || c == '/' || c == '%') {
		vr = exp();

		switch (c) {
		case '*':
			vl *= vr;
			break;
		case '/':
			vl /= vr;
			break;
		case '%':
			vl %= vr;
			break;
		}
	}
	ungetch();
	return vl;
}

/*
 * <term> := <unary> { <expop> <unary> }
 */
static int
exp()
{
	register c, vl, vr, n;

	vl = unary();
	switch (c = skipws()) {

	case '*':
		if (getch() != '*') {
			ungetch();
			break;
		}

	case '^':
		vr = exp();
		n = 1;
		while (vr-- > 0)
			n *= vl;
		return n;
	}

	ungetch();
	return vl;
}

/*
 * unary : factor | unop unary
 */
static int
unary()
{
	register int val, c;

	if ((c = skipws()) == '+' || c == '-' || c == '~') {
		val = unary();

		switch (c) {
		case '+':
			return val;
		case '-':
			return -val;
		case '~':
			return ~val;
		}
	}

	ungetch();
	return factor();
}

/*
 * factor : constant | '(' query ')'
 */
static int
factor()
{
	register int val;

	if (skipws() == '(') {
		val = query();
		if (skipws() != ')')
			experr("bad factor");
		return val;
	}

	ungetch();
	return constant();
}

/*
 * constant: num | 'char'
 * Note: constant() handles multi-byte constants
 */
static int
constant()
{
	register int i;
	register int value;
	register char c;
	int v[sizeof(int)];

	if (skipws() != '\'') {
		ungetch();
		return num();
	}
	for (i = 0; i < sizeof(int); i++) {
		if ((c = getch()) == '\'') {
			ungetch();
			break;
		}
		if (c == '\\') {
			switch (c = getch()) {
			case '0':
			case '1':
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
				ungetch();
				c = num();
				break;
			case 'n':
				c = 012;
				break;
			case 'r':
				c = 015;
				break;
			case 't':
				c = 011;
				break;
			case 'b':
				c = 010;
				break;
			case 'f':
				c = 014;
				break;
			}
		}
		v[i] = c;
	}
	if (i == 0 || getch() != '\'')
		experr("illegal character constant");
	for (value = 0; --i >= 0;) {
		value <<= 8;
		value += v[i];
	}
	return value;
}

/*
 * num : digit | num digit
 */
static int
num()
{
	register int rval, c, base;
	int ndig;

	base = ((c = skipws()) == '0') ? OCTAL : DECIMAL;
	rval = 0;
	ndig = 0;
	while (c >= '0' && c <= (base == OCTAL ? '7' : '9')) {
		rval *= base;
		rval += (c - '0');
		c = getch();
		ndig++;
	}
	ungetch();

	if (ndig == 0)
		experr("bad constant");

	return rval;

}

/*
 * eqrel : '=' | '==' | '!=' | '<' | '>' | '<=' | '>='
 */
static int
geteqrel()
{
	register int c1, c2;

	c1 = skipws();
	c2 = getch();

	switch (c1) {

	case '=':
		if (c2 != '=')
			ungetch();
		return EQL;

	case '!':
		if (c2 == '=')
			return NEQ;
		ungetch();
		ungetch();
		return -1;

	case '<':
		if (c2 == '=')
			return LEQ;
		ungetch();
		return LSS;

	case '>':
		if (c2 == '=')
			return GEQ;
		ungetch();
		return GTR;

	default:
		ungetch();
		ungetch();
		return -1;
	}
}

/*
 * Skip over any white space and return terminating char.
 */
static int
skipws()
{
	register char c;

	while ((c = getch()) <= ' ' && c > EOS)
		;
	return c;
}

/*
 * resets environment to eval(), prints an error
 * and forces eval to return FALSE.
 */
static void
experr(msg)
char *msg;
{
	printf("m4: %s in expr.\n", msg);
	longjmp(expjump, -1);
}