rexp.c

/********************************************
rexp.c
copyright 2008-2009,2010, Thomas E. Dickey
copyright 1991-1993,1996, Michael D. Brennan

This is a source file for mawk, an implementation of
the AWK programming language.

Mawk is distributed without warranty under the terms of
the GNU General Public License, version 2, 1991.
********************************************/

/*
 * $MawkId: rexp.c,v 1.14 2010/08/04 00:23:35 tom Exp $
 * @Log: rexp.c,v @
 * Revision 1.3  1996/09/02 18:47:36  mike
 * Make ^* and ^+ syntax errors.
 *
 * Revision 1.2  1993/07/23 13:21:32  mike
 * cleanup rexp code
 *
 * Revision 1.1.1.1  1993/07/03	 18:58:26  mike
 * move source to cvs
 *
 * Revision 3.4	 1991/08/13  09:09:59  brennan
 * VERSION .9994
 *
 * Revision 3.3	 91/08/04  15:45:03  brennan
 * no longer attempt to recover mem on failed REcompile
 * Its not worth the effort
 *
 * Revision 3.2	 91/08/03  07:24:06  brennan
 * check for empty machine stack (missing operand) wasn't quite right
 *
 * Revision 3.1	 91/06/07  10:33:16  brennan
 * VERSION 0.995
 *
 * Revision 1.7	 91/06/05  08:58:47  brennan
 * change RE_free to free
 *
 * Revision 1.6	 91/06/03  07:07:17  brennan
 * moved parser stacks inside REcompile
 * removed unnecessary copying
 *
 */

/*  op precedence  parser for regular expressions  */

#include "rexp.h"
#include "regexp.h"

/*  DATA   */
int REerrno;
const char *REerrlist[] =
{(char *) 0,
 /* 1  */ "missing '('",
 /* 2  */ "missing ')'",
 /* 3  */ "bad class -- [], [^] or [",
 /* 4  */ "missing operand",
 /* 5  */ "resource exhaustion -- regular expression too large",
 /* 6  */ "syntax error ^* or ^+"
};
/* E5 is very unlikely to occur */

/* This table drives the operator precedence parser */
/* *INDENT-OFF* */
static  short  table[8][8]  =  {
/*        0   |   CAT   *   +   ?   (   )   */
/* 0 */   {0,  L,  L,    L,  L,  L,  L,  E1},
/* | */   {G,  G,  L,    L,  L,  L,  L,  G},
/* CAT*/  {G,  G,  G,    L,  L,  L,  L,  G},
/* * */   {G,  G,  G,    G,  G,  G,  E7, G},
/* + */   {G,  G,  G,    G,  G,  G,  E7, G},
/* ? */   {G,  G,  G,    G,  G,  G,  E7, G},
/* ( */   {E2, L,  L,    L,  L,  L,  L,  EQ},
/* ) */   {G , G,  G,    G,  G,  G,  E7, G}     }   ;
/* *INDENT-ON* */

#define	 STACKSZ   64

static jmp_buf err_buf;		/*  used to trap on error */

void
RE_error_trap(int x)
{
    REerrno = x;
    longjmp(err_buf, 1);
}

PTR
REcompile(char *re, size_t len)
{
    MACHINE m_stack[STACKSZ];
    struct op {
	int token;
	int prec;
    } op_stack[STACKSZ];
    register MACHINE *m_ptr;
    register struct op *op_ptr;
    register int t;

    /* do this first because it also checks if we have a
       run time stack */
    RE_lex_init(re, len);

    if (len == 0) {
	STATE *p = (STATE *) RE_malloc(sizeof(STATE));
	p->s_type = M_ACCEPT;
	return (PTR) p;
    }

    if (setjmp(err_buf))
	return (PTR) 0;
    /* we used to try to recover memory left on machine stack ;
       but now m_ptr is in a register so it won't be right unless
       we force it out of a register which isn't worth the trouble */

    /* initialize the stacks  */
    m_ptr = m_stack - 1;
    op_ptr = op_stack;
    op_ptr->token = 0;

    t = RE_lex(m_stack);

    while (1) {
	switch (t) {
	case T_STR:
	case T_ANY:
	case T_U:
	case T_START:
	case T_END:
	case T_CLASS:
	    m_ptr++;
	    break;

	case 0:		/*  end of reg expr   */
	    if (op_ptr->token == 0) {
		/*  done   */
		if (m_ptr == m_stack)
		    return (PTR) m_ptr->start;
		else {
		    /* machines still on the stack  */
		    RE_panic("values still on machine stack");
		}
	    }

	    /*  otherwise  fall  thru to default
	       which is operator case  */

	default:

	    if ((op_ptr->prec = table[op_ptr->token][t]) == G) {
		do {		/* op_pop   */

		    if (op_ptr->token <= T_CAT)		/*binary op */
			m_ptr--;
		    /* if not enough values on machine stack
		       then we have a missing operand */
		    if (m_ptr < m_stack)
			RE_error_trap(-E4);

		    switch (op_ptr->token) {
		    case T_CAT:
			RE_cat(m_ptr, m_ptr + 1);
			break;

		    case T_OR:
			RE_or(m_ptr, m_ptr + 1);
			break;

		    case T_STAR:
			RE_close(m_ptr);
			break;

		    case T_PLUS:
			RE_poscl(m_ptr);
			break;

		    case T_Q:
			RE_01(m_ptr);
			break;

		    default:
			/*nothing on ( or ) */
			break;
		    }

		    op_ptr--;
		}
		while (op_ptr->prec != L);

		continue;	/* back thru switch at top */
	    }

	    if (op_ptr->prec < 0) {
		if (op_ptr->prec == E7)
		    RE_panic("parser returns E7");
		else
		    RE_error_trap(-op_ptr->prec);
	    }

	    if (++op_ptr == op_stack + STACKSZ) {
		/* stack overflow */
		RE_error_trap(-E5);
	    }

	    op_ptr->token = t;
	}			/* end of switch */

	if (m_ptr == m_stack + (STACKSZ - 1)) {
	    /*overflow */
	    RE_error_trap(-E5);
	}

	t = RE_lex(m_ptr + 1);
    }
}

void
REdestroy(PTR ptr)
{
    int done = 0;
    int n = 0;
    STATE *q = (STATE *) ptr;

    TRACE(("REdestroy %p\n", q));
    while (!done) {
	TRACE(("...%d type %d\n", n, q->s_type));
	switch (q->s_type) {
	case M_ACCEPT:
	    done = 1;
	    break;
	case M_STR:
	    RE_free(q->s_data.str);
	    break;
	default:
	    if (q->s_type < 0 || q->s_type > END_ON)
		done = -1;
	    break;
	}
	++q;
	++n;
    }
    RE_free(ptr);
}

/* getting here means a logic flaw or unforeseen case */
void
RE_panic(const char *s)
{
    fprintf(stderr, "REcompile() - panic:  %s\n", s);
    mawk_exit(100);
}

/* getting regexp error message */
const char *
REerror(void)
{
    return REerrlist[REerrno];
}