qse/qse/lib/cmn/rex.c

/*
 * $Id$
 * 
    Copyright 2006-2014 Chung, Hyung-Hwan.
    This file is part of QSE.

    QSE is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as 
    published by the Free Software Foundation, either version 3 of 
    the License, or (at your option) any later version.

    QSE 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public 
    License along with QSE. If not, see <http://www.gnu.org/licenses/>.
 */

#include <qse/cmn/rex.h>
#include <qse/cmn/chr.h>
#include <qse/cmn/str.h>
#include <qse/cmn/lda.h>
#include "mem.h"

#define OCC_MAX QSE_TYPE_MAX(qse_size_t)

/*#define XTRA_DEBUG*/

typedef struct comp_t comp_t;
struct comp_t
{
	qse_rex_t* rex;

	qse_cstr_t re;

	const qse_char_t* ptr;
	const qse_char_t* end;

	struct
	{
		qse_cint_t value;
		int escaped;
	} c;

	qse_size_t gdepth; /* group depth */
	qse_rex_node_t* start;
};

typedef struct exec_t exec_t;
struct exec_t
{
	qse_rex_t* rex;

	struct
	{
		const qse_char_t* ptr;
		const qse_char_t* end;
	} str;

	struct
	{
		const qse_char_t* ptr;
		const qse_char_t* end;
	} sub;

	struct
	{
		int active;
		int pending;
		qse_lda_t set[2]; /* candidate arrays */
	} cand;

	qse_size_t nmatches;
	const qse_char_t* matchend; /* 1 character past the match end */
};

typedef struct pair_t pair_t;
struct pair_t
{
	qse_rex_node_t* head;
	qse_rex_node_t* tail;
};

/* The group_t type defines a structure to maintain the nested
 * traces of subgroups. The actual traces are maintained in a stack
 * of sinlgly linked group_t elements. The head element acts
 * as a management element where the occ field is a reference count
 * and the node field is QSE_NULL always 
 */
typedef struct group_t group_t;
struct group_t
{
	qse_rex_node_t* node;
	qse_size_t occ; 
	group_t* next;
};

typedef struct cand_t cand_t;
struct cand_t
{
	qse_rex_node_t*   node;

	/* occurrence */
	qse_size_t        occ;

	/* the stack of groups that this candidate belongs to. 
	 * it is in the singliy linked list form */
	group_t*          group;

	/* match pointer. the number of character advancement 
	 * differs across various node types. BOL and EOL don't advance to
	 * the next character on match while ANY and CHAR do on match.
	 * therefore, the match pointer is managed per candidate basis. */
	const qse_char_t* mptr; 
};

int qse_rex_init (qse_rex_t* rex, qse_mmgr_t* mmgr, qse_rex_node_t* code)
{
	QSE_MEMSET (rex, 0, QSE_SIZEOF(*rex));
	rex->mmgr = mmgr;

	QSE_ASSERT (code == QSE_NULL || code->id == QSE_REX_NODE_START);

	/* note that passing a compiled expression to qse_rex_open() 
	 * is to delegate it to this rex object. when this rex object
	 * is closed, the code delegated is destroyed. */

	rex->code = code;
	return 0;
}

qse_rex_t* qse_rex_open (qse_mmgr_t* mmgr, qse_size_t xtnsize, qse_rex_node_t* code)
{
	qse_rex_t* rex;

	rex = (qse_rex_t*) QSE_MMGR_ALLOC (mmgr, QSE_SIZEOF(qse_rex_t) + xtnsize);
	if (rex == QSE_NULL) return QSE_NULL;

	if (qse_rex_init (rex, mmgr, code) <= -1)
	{
		QSE_MMGR_FREE (mmgr, rex);
		return QSE_NULL;
	}

	QSE_MEMSET (QSE_XTN(rex), 0, xtnsize);
	return rex;
}

static void freenode (qse_rex_node_t* node, qse_mmgr_t* mmgr)
{
	if (node->id == QSE_REX_NODE_CSET)
	{
		if (node->u.cset.member != QSE_NULL) 
			qse_str_close (node->u.cset.member);
	}

	QSE_MMGR_FREE (mmgr, node);
}

static void freeallnodes (qse_rex_node_t* start)
{
	qse_rex_node_t* x, * y;
	qse_mmgr_t* mmgr;

	QSE_ASSERT (start->id == QSE_REX_NODE_START);

	mmgr = start->u.s.mmgr;
	x = start->u.s.link;
	while (x != QSE_NULL)
	{
		y = x; x = x->link;
		freenode (y, mmgr);
	}

	QSE_MMGR_FREE (mmgr, start);
}

void qse_rex_fini (qse_rex_t* rex)
{
	if (rex->code != QSE_NULL) 
	{
		freeallnodes (rex->code);
		rex->code = QSE_NULL;
	}
}

void qse_rex_close (qse_rex_t* rex)
{
	qse_rex_fini (rex);
	QSE_MMGR_FREE (rex->mmgr, rex);
}

qse_mmgr_t* qse_rex_getmmgr (qse_rex_t* rex)
{
	return rex->mmgr;
}

void* qse_rex_getxtn (qse_rex_t* rex)
{
	return QSE_XTN (rex);
}

qse_rex_node_t* qse_rex_yield (qse_rex_t* rex)
{
	qse_rex_node_t* code = rex->code;
	rex->code = QSE_NULL;
	return code;
}

int qse_rex_getoption (const qse_rex_t* rex)
{
	return rex->option;
}

void qse_rex_setoption (qse_rex_t* rex, int opts)
{
	rex->option = opts;
}

qse_rex_errnum_t qse_rex_geterrnum (const qse_rex_t* rex)
{
	return rex->errnum;
}

const qse_char_t* qse_rex_geterrmsg (const qse_rex_t* rex)
{
	static const qse_char_t* errstr[] = 
	{
		QSE_T("no error"),
		QSE_T("other error"),
		QSE_T("not implemented"),
		QSE_T("subsystem error"),
		QSE_T("internal error that should never have happened"),

		QSE_T("no sufficient memory available"),
		QSE_T("no expression compiled"),
		QSE_T("recursion too deep"),
		QSE_T("right parenthesis expected"),
		QSE_T("right bracket expected"),
		QSE_T("right brace expected"),
		QSE_T("colon expected"),
		QSE_T("invalid character range"),
		QSE_T("invalid character class"),
		QSE_T("invalid occurrence bound"),
		QSE_T("special character at wrong position"),
		QSE_T("premature expression end")
	};
	
	return (rex->errnum >= 0 && rex->errnum < QSE_COUNTOF(errstr))?
		errstr[rex->errnum]: QSE_T("unknown error");
}

static qse_rex_node_t* newnode (comp_t* c, qse_rex_node_id_t id)
{
	qse_rex_node_t* node;

	/* TODO: performance optimization.
	 *       preallocate a large chunk of memory and allocate a node
	 *       from the chunk. increase the chunk if it has been used up.
	 */

	node = (qse_rex_node_t*) 
		QSE_MMGR_ALLOC (c->rex->mmgr, QSE_SIZEOF(qse_rex_node_t));
	if (node == QSE_NULL) 
	{
		c->rex->errnum = QSE_REX_ENOMEM;
		return QSE_NULL;
	}

	QSE_MEMSET (node, 0, QSE_SIZEOF(*node));
	node->id = id;

	if (c->start != QSE_NULL) 
	{
		QSE_ASSERT (c->start->id == QSE_REX_NODE_START);
		node->link = c->start->u.s.link;
		c->start->u.s.link = node;
	}

	return node;
}

static qse_rex_node_t* newstartnode (comp_t* c)
{
	qse_rex_node_t* n = newnode (c, QSE_REX_NODE_START);
	if (n != QSE_NULL) 
	{
		n->u.s.mmgr = c->rex->mmgr;
		n->u.s.link = QSE_NULL;
	}
	return n;
}

static qse_rex_node_t* newendnode (comp_t* c)
{
	return newnode (c, QSE_REX_NODE_END);
}

static qse_rex_node_t* newnopnode (comp_t* c)
{
	return newnode (c, QSE_REX_NODE_NOP);
}

static qse_rex_node_t* newgroupnode (comp_t* c)
{
	return newnode (c, QSE_REX_NODE_GROUP);
}

static qse_rex_node_t* newgroupendnode (comp_t* c, qse_rex_node_t* group)
{
	qse_rex_node_t* n = newnode (c, QSE_REX_NODE_GROUPEND);
	if (n != QSE_NULL) n->u.ge.group = group;
	return n;
}

static qse_rex_node_t* newcharnode (comp_t* c, qse_char_t ch)
{
	qse_rex_node_t* n = newnode (c, QSE_REX_NODE_CHAR);
	if (n != QSE_NULL) n->u.c = ch;
	return n;
}

static qse_rex_node_t* newbranchnode (
	comp_t* c, qse_rex_node_t* left, qse_rex_node_t* alter)
{
	qse_rex_node_t* n = newnode (c, QSE_REX_NODE_BRANCH);
	if (n != QSE_NULL)
	{
		/*n->u.b.left = left; */
		n->next = left;
		n->u.b.alter = alter;
	}
	return n;
}

#define CHECK_END(com) \
	do { \
		if (com->ptr >= com->end) \
		{ \
			com->rex->errnum = QSE_REX_EPREEND; \
			return -1; \
		} \
	} while(0)

#define IS_HEX(c) \
	((c >= QSE_T('0') && c <= QSE_T('9')) || \
	 (c >= QSE_T('A') && c <= QSE_T('F')) || \
	 (c >= QSE_T('a') && c <= QSE_T('f')))

#define HEX_TO_NUM(c) \
	((c >= QSE_T('0') && c <= QSE_T('9'))? c-QSE_T('0'):  \
	 (c >= QSE_T('A') && c <= QSE_T('F'))? c-QSE_T('A')+10: \
	                                       c-QSE_T('a')+10)

#define IS_SPE(com,ch) ((com)->c.value == (ch) && !(com)->c.escaped)
#define IS_ESC(com) ((com)->c.escaped)
#define IS_EOF(com) ((com)->c.value == QSE_CHAR_EOF)

#define getc_noesc(c) getc(c,1)
#define getc_esc(c)   getc(c,0)

static int getc (comp_t* com, int noesc)
{
	qse_char_t c;

	if (com->ptr >= com->end)
	{
		com->c.value = QSE_CHAR_EOF;
		com->c.escaped = 0;
		return 0;
	}

	com->c.value = *com->ptr++;
	com->c.escaped = 0;

	if (noesc || com->c.value != QSE_T('\\')) return 0;

	CHECK_END (com);
	c = *com->ptr++;

	if (c == QSE_T('n')) c = QSE_T('\n');
	else if (c == QSE_T('r')) c = QSE_T('\r');
	else if (c == QSE_T('t')) c = QSE_T('\t');
	else if (c == QSE_T('f')) c = QSE_T('\f');
	else if (c == QSE_T('b')) c = QSE_T('\b');
	else if (c == QSE_T('v')) c = QSE_T('\v');
	else if (c == QSE_T('a')) c = QSE_T('\a');

#if 0
	/* backrefernce conflicts with octal notation */
	else if (c >= QSE_T('0') && c <= QSE_T('7')) 
	{
		qse_char_t cx;

		c = c - QSE_T('0');

		CHECK_END (com);
		cx = *com->ptr++;
		if (cx >= QSE_T('0') && cx <= QSE_T('7'))
		{
			c = c * 8 + cx - QSE_T('0');

			CHECK_END (com);
			cx = *com->ptr++;
			if (cx >= QSE_T('0') && cx <= QSE_T('7'))
			{
				c = c * 8 + cx - QSE_T('0');
			}
		}
	}
#endif

	else if (c == QSE_T('x')) 
	{
		qse_char_t cx;

		CHECK_END (com);
		cx = *com->ptr++;
		if (IS_HEX(cx))
		{
			c = HEX_TO_NUM(cx);

			CHECK_END (com);
			cx = *com->ptr++;
			if (IS_HEX(cx))
			{
				c = c * 16 + HEX_TO_NUM(cx);
			}
		}
	}
#if defined(QSE_CHAR_IS_WCHAR)
	else if (c == QSE_T('u') && QSE_SIZEOF(qse_char_t) >= 2) 
	{
		qse_char_t cx;

		CHECK_END (com);
		cx = *com->ptr++;
		if (IS_HEX(cx))
		{
			qse_size_t i;

			c = HEX_TO_NUM(cx);

			for (i = 0; i < 3; i++)
			{
				CHECK_END (com);
				cx = *com->ptr++;

				if (!IS_HEX(cx)) break;
				c = c * 16 + HEX_TO_NUM(cx);
			}
		}
	}
	else if (c == QSE_T('U') && QSE_SIZEOF(qse_char_t) >= 4) 
	{
		qse_char_t cx;

		CHECK_END (com);
		cx = *com->ptr++;
		if (IS_HEX(cx))
		{
			qse_size_t i;

			c = HEX_TO_NUM(cx);

			for (i = 0; i < 7; i++)
			{
				CHECK_END (com);
				cx = *com->ptr++;

				if (!IS_HEX(cx)) break;
				c = c * 16 + HEX_TO_NUM(cx);
			}
		}
	}
#endif

	com->c.value = c;
	com->c.escaped = QSE_TRUE;

#if 0
	com->c = (com->ptr < com->end)? *com->ptr++: QSE_CHAR_EOF;
if (com->c == QSE_CHAR_EOF)
qse_printf (QSE_T("getc => <EOF>\n"));
else qse_printf (QSE_T("getc => %c\n"), com->c);
#endif
	return 0;
}

struct ccinfo_t
{
	qse_cstr_t name;
	int (*func) (exec_t* e, qse_char_t c);
}; 

#define ISBLANK(c) ((c) == QSE_T(' ') || (c) == QSE_T('\t'))

static int cc_isalnum (exec_t* e, qse_char_t c) { return QSE_ISALNUM (c); }
static int cc_isalpha (exec_t* e, qse_char_t c) { return QSE_ISALPHA (c); }
static int cc_isblank (exec_t* e, qse_char_t c) { return QSE_ISBLANK(c); }
static int cc_iscntrl (exec_t* e, qse_char_t c) { return QSE_ISCNTRL (c); }
static int cc_isdigit (exec_t* e, qse_char_t c) { return QSE_ISDIGIT (c); }
static int cc_isgraph (exec_t* e, qse_char_t c) { return QSE_ISGRAPH (c); }

static int cc_islower (exec_t* e, qse_char_t c) 
{ 
	if (e->rex->option & QSE_REX_IGNORECASE) return !0;
	return QSE_ISLOWER (c); 
}

static int cc_isprint (exec_t* e, qse_char_t c) { return QSE_ISPRINT (c); }
static int cc_ispunct (exec_t* e, qse_char_t c) { return QSE_ISPUNCT (c); }
static int cc_isspace (exec_t* e, qse_char_t c) { return QSE_ISSPACE (c); }

static int cc_isupper (exec_t* e, qse_char_t c) 
{ 
	if (e->rex->option & QSE_REX_IGNORECASE) return !0;
	return QSE_ISUPPER (c); 
}

static int cc_isxdigit (exec_t* e, qse_char_t c) { return QSE_ISXDIGIT (c); }

static int cc_isword (exec_t* e, qse_char_t c) 
{
	return QSE_ISALNUM (c) || c == QSE_T('_'); 
}

static struct ccinfo_t ccinfo[] =
{
	{ { QSE_T("alnum"),  5 }, cc_isalnum },
	{ { QSE_T("alpha"),  5 }, cc_isalpha },
	{ { QSE_T("blank"),  5 }, cc_isblank },
	{ { QSE_T("cntrl"),  5 }, cc_iscntrl },
	{ { QSE_T("digit"),  5 }, cc_isdigit },
	{ { QSE_T("graph"),  5 }, cc_isgraph },
	{ { QSE_T("lower"),  5 }, cc_islower },
	{ { QSE_T("print"),  5 }, cc_isprint },
	{ { QSE_T("punct"),  5 }, cc_ispunct },
	{ { QSE_T("space"),  5 }, cc_isspace },
	{ { QSE_T("upper"),  5 }, cc_isupper },
	{ { QSE_T("xdigit"), 6 }, cc_isxdigit },
	{ { QSE_T("word"),   4 }, cc_isword },

	/*
	{ { QSE_T("arabic"),   6 }, cc_isarabic },
	{ { QSE_T("chinese"),  7 }, cc_ischinese },
	{ { QSE_T("english"),  7 }, cc_isenglish },
	{ { QSE_T("japanese"), 8 }, cc_isjapanese },
	{ { QSE_T("korean"),   6 }, cc_iskorean }, 
	{ { QSE_T("thai"),     4 }, cc_isthai }, 
	*/

	{ { QSE_NULL,          0 }, QSE_NULL }
};

static int charclass (comp_t* com)
{
	const struct ccinfo_t* ccp = ccinfo;
	qse_size_t len = com->end - com->ptr;

	while (ccp->name.ptr != QSE_NULL)
	{
		if (qse_strxbeg(com->ptr,len,ccp->name.ptr) != QSE_NULL) break;
		ccp++;
	}

	if (ccp->name.ptr == QSE_NULL)
	{
		/* wrong class name */
		com->rex->errnum = QSE_REX_ECCLASS;
		return -1;
	}

	com->ptr += ccp->name.len;

	if (getc_noesc(com) <= -1) return -1;
	if (com->c.value != QSE_T(':'))
	{
		com->rex->errnum = QSE_REX_ECCLASS;
		return -1;
	}

	if (getc_noesc(com) <= -1) return -1;
	if (com->c.value != QSE_T(']'))
	{
		com->rex->errnum = QSE_REX_ERBRACK;	
		return -1;
	}

	if (getc_esc(com) <= -1) return -1;
	return (int)(ccp - ccinfo);
}

#define ADD_CSET_CODE(com,node,code,len) \
	do { if (add_cset_code(com,node,code,len) <= -1) return -1; } while(0)

static int add_cset_code (
	comp_t* com, qse_rex_node_t* node, const qse_char_t* c, qse_size_t l)
{
	if (qse_str_ncat(node->u.cset.member,c,l) == (qse_size_t)-1)
	{
		com->rex->errnum = QSE_REX_ENOMEM;
		return -1;
	}
	return 0;
}

static int charset (comp_t* com, qse_rex_node_t* node)
{
	QSE_ASSERT (node->id == QSE_REX_NODE_CSET);
	QSE_ASSERT (node->u.cset.negated == 0);
	QSE_ASSERT (node->u.cset.member	== QSE_NULL);

	if (IS_SPE(com,QSE_T('^')))
	{
		/* negate an expression */
		node->u.cset.negated = 1;
		if (getc_noesc(com) <= -1) return -1;
	}


	/* initialize the member array */
	node->u.cset.member = qse_str_open (com->rex->mmgr, 0, 64);
	if (node->u.cset.member == QSE_NULL)
	{
		com->rex->errnum = QSE_REX_ENOMEM;
		return -1;
	}

	/* if ] is the first character or the second character following ^,
	 * it is treated literally */

	do
	{
		int x1, x2;
		qse_char_t c1, c2;

		x1 = com->c.escaped;
		c1 = com->c.value;
		if (c1 == QSE_CHAR_EOF)
		{
			com->rex->errnum = QSE_REX_EPREEND;
			return -1;
		}

		if (getc_esc(com) <= -1) return -1;
		x2 = com->c.escaped;
		c2 = com->c.value;

		if (!x1 && c1 == QSE_T('[') && 
		    !x2 && c2 == QSE_T(':'))
		{
			int n;
			qse_char_t tmp[2];

			/* begins with [: 
			 * don't read in the next character as charclass() 
			 * matches a class name differently from other routines.
			 * if (getc_noesc(com) <= -1) return -1;
			 */
			if ((n = charclass(com)) <= -1) return -1;
			
			QSE_ASSERT (n < QSE_TYPE_MAX(qse_char_t));

			tmp[0] = QSE_REX_CSET_CLASS;
			tmp[1] = n;
			ADD_CSET_CODE (com, node, tmp, QSE_COUNTOF(tmp));
		}
		else if (!x2 && c2 == QSE_T('-'))
		{
			if (getc_esc(com) <= -1) return -1;
			if (IS_SPE(com, QSE_T(']')))
			{
				qse_char_t tmp[4];

				/* '-' is the last character in the set.
				 * treat it literally */

				tmp[0] = QSE_REX_CSET_CHAR;
				tmp[1] = c1;
				tmp[2] = QSE_REX_CSET_CHAR;
				tmp[3] = c2;

				ADD_CSET_CODE (com, node, tmp, QSE_COUNTOF(tmp));
				break;
			}

			if (c1 > com->c.value)
			{
				/* range end must be >= range start */
				com->rex->errnum = QSE_REX_ECRANGE;
				return -1;
			}
			else if (c1 == com->c.value)
			{
				/* if two chars in the range are the same,
				 * treat it as a single character */
				qse_char_t tmp[2];
				tmp[0] = QSE_REX_CSET_CHAR;
				tmp[1] = c1;
				ADD_CSET_CODE (com, node, tmp, QSE_COUNTOF(tmp));
			}
			else
			{
				qse_char_t tmp[3];
				tmp[0] = QSE_REX_CSET_RANGE;
				tmp[1] = c1;
				tmp[2] = com->c.value;
				ADD_CSET_CODE (com, node, tmp, QSE_COUNTOF(tmp));
			}
			
			if (getc_esc(com) <= -1) return -1;
		}
		else
		{
			qse_char_t tmp[2];
			tmp[0] = QSE_REX_CSET_CHAR;
			tmp[1] = c1;
			ADD_CSET_CODE (com, node, tmp, QSE_COUNTOF(tmp));
		}
	}
	while (!IS_SPE(com,QSE_T(']')));

	if (getc_esc(com) <= -1) return -1;
	return 0;
}

static int occbound (comp_t* com, qse_rex_node_t* n)
{
	qse_size_t bound;

	bound = 0;
	while (com->c.value >= QSE_T('0') && com->c.value <= QSE_T('9'))
	{
		bound = bound * 10 + com->c.value - QSE_T('0');
		if (getc_noesc(com) <= -1) return -1;
	}

	n->occ.min = bound;

	if (com->c.value == QSE_T(',')) 
	{
		if (getc_noesc(com) <= -1) return -1;

		if (com->c.value >= QSE_T('0') && com->c.value <= QSE_T('9'))
		{
			bound = 0;

			do
			{
				bound = bound * 10 + com->c.value - QSE_T('0');
				if (getc_noesc(com) <= -1) return -1;
			}
			while (com->c.value >= QSE_T('0') && 
			       com->c.value <= QSE_T('9'));

			n->occ.max = bound;
		}
		else n->occ.max = OCC_MAX;
	}
	else n->occ.max = n->occ.min;

	if (n->occ.min > n->occ.min)
	{
		/* invalid occurrences range */
		com->rex->errnum = QSE_REX_EBOUND;
		return -1;
	}

	if (com->c.value != QSE_T('}'))
	{
		com->rex->errnum = QSE_REX_ERBRACE;
		return -1;
	}

	if (getc_esc(com) <= -1) return -1;
	return 0;
}

static qse_rex_node_t* comp_branches (comp_t* com, qse_rex_node_t* ge);

static qse_rex_node_t* comp_group (comp_t* com)
{
	/* enter a subgroup */
	qse_rex_node_t* body, *g, * ge;

	g = newgroupnode (com);
	if (g == QSE_NULL) return QSE_NULL;

	ge = newgroupendnode (com, g);
	if (ge == QSE_NULL) return QSE_NULL;

	/* skip '(' */
	if (getc_esc(com) <= -1) return QSE_NULL;

	com->gdepth++;

	/* pass the GROUPEND node so that the
	 * last node in the subgroup links to
	 * this GROUPEND node. */
	body = comp_branches (com, ge);
	if (body == QSE_NULL) return QSE_NULL;

	if (!IS_SPE(com,QSE_T(')')))
	{
		com->rex->errnum = QSE_REX_ERPAREN;
		return QSE_NULL;
	}

	com->gdepth--;

	/* skip ')' */
	if (getc_esc(com) <= -1) return QSE_NULL;

	g->u.g.head = body;
	g->u.g.end = ge;

	return g;
}

static qse_rex_node_t* comp_occ (comp_t* com, qse_rex_node_t* atom)
{
	switch (com->c.value)
	{
		case QSE_T('?'):
			atom->occ.min = 0;
			atom->occ.max = 1;
			if (getc_esc(com) <= -1) return QSE_NULL;
			break;
		
		case QSE_T('*'):
			atom->occ.min = 0;
			atom->occ.max = OCC_MAX;
			if (getc_esc(com) <= -1) return QSE_NULL;
			break;

		case QSE_T('+'):
			atom->occ.min = 1;
			atom->occ.max = OCC_MAX;
			if (getc_esc(com) <= -1) return QSE_NULL;
			break;

		case QSE_T('{'):
			if (!(com->rex->option & QSE_REX_NOBOUND))
			{
				if (getc_noesc(com) <= -1 ||
				    occbound(com,atom) <= -1) return QSE_NULL;
			}
			break;
	}

	return atom;
}

static qse_rex_node_t* comp_atom (comp_t* com)
{
	qse_rex_node_t* atom;

	if (!IS_ESC(com))
	{
		switch (com->c.value)
		{
			case QSE_T('('):
				atom = comp_group (com);
				if (atom == QSE_NULL) return QSE_NULL;
				break;
			
			case QSE_T('.'):
				atom = newnode (com, QSE_REX_NODE_ANY);
				if (atom == QSE_NULL) return QSE_NULL;
				if (getc_esc(com) <= -1) return QSE_NULL;
				break;

			case QSE_T('^'):
				atom = newnode (com, QSE_REX_NODE_BOL);
				if (atom == QSE_NULL) return QSE_NULL;
				if (getc_esc(com) <= -1) return QSE_NULL;
				break;
	
			case QSE_T('$'):
				atom = newnode (com, QSE_REX_NODE_EOL);
				if (atom == QSE_NULL) return QSE_NULL;
				if (getc_esc(com) <= -1) return QSE_NULL;
				break;

			case QSE_T('['):
				atom = newnode (com, QSE_REX_NODE_CSET);
				if (atom == QSE_NULL) return QSE_NULL;
				if (getc_esc(com) <= -1) return QSE_NULL;
				if (charset(com, atom) <= -1) return QSE_NULL;
				break;

			default:
				if (com->rex->option & QSE_REX_STRICT)
				{
					/* check if a special charcter is at the 
					 * position that requires a normal character. */
					switch (com->c.value)
					{
						case QSE_T('{'):
							/* { is a normal charcter when bound is disabled */
							if (com->rex->option & QSE_REX_NOBOUND) break;

						case QSE_T(')'):
						case QSE_T('?'):
						case QSE_T('*'):
						case QSE_T('+'):
							/* it's at the wrong postion */
							com->rex->errnum = QSE_REX_ESPCAWP;
							return QSE_NULL;
					}
				}

				goto normal_char;
		}
	}
	else
	{
	normal_char:
		/* normal character */
		atom = newcharnode (com, com->c.value);
		if (atom == QSE_NULL) return QSE_NULL;
		if (getc_esc(com) <= -1) return QSE_NULL;
	}

	atom->occ.min = 1;
	atom->occ.max = 1;

	if (!IS_ESC(com))
	{
		/* handle the occurrence specifier, if any */
		if (comp_occ (com, atom) == QSE_NULL) return QSE_NULL;
	}

	return atom;
}

#if 0
static qse_rex_node_t* zero_or_more (comp_t* c, qse_rex_node_t* atom)
{
	qse_rex_node_t* b;

	b = newbranchnode (c, QSE_NULL, atom);
	if (b == QSE_NULL) return QSE_NULL;
	
	atom->occ.min = 1;
	atom->occ.max = 1;
	atom->next = b;	
	
	return b;
}

static qse_rex_node_t* one_or_more (comp_t* c, qse_rex_node_t* atom)
{
	qse_rex_node_t* b;

	b = newbranchnode (c, atom, QSE_NULL);

	atom->occ.min = 1;
	atom->occ.max = 1;
	atom->next = b;	

	TODO: return b as the tail....
	return atom;
}
#endif

static qse_rex_node_t* pseudo_group (comp_t* c, qse_rex_node_t* atom)
{
	qse_rex_node_t* g, *ge, * b;

	QSE_ASSERT (atom->occ.min <= 0);

	g = newgroupnode (c);
	if (g == QSE_NULL) return QSE_NULL;

	ge = newgroupendnode (c, g);
	if (ge == QSE_NULL) return QSE_NULL;

	b = newbranchnode (c, atom, ge);
	if (b == QSE_NULL) return QSE_NULL;

	atom->occ.min = 1;
	atom->next = ge;
	QSE_ASSERT (atom->occ.max >= atom->occ.min);

	g->occ.max = 1;
	g->occ.min = 1;
	g->u.g.end = ge;
	g->u.g.head = b;
	g->u.g.pseudo = 1;
	ge->u.ge.pseudo = 1;

	return g;
}

/* compile a list of atoms at the outermost level and/or
 * within a subgroup */
static qse_rex_node_t* comp_branch (comp_t* c, pair_t* pair)
{
#define REACHED_END(c) \
	(IS_EOF(c) || IS_SPE(c,QSE_T('|')) || \
	 (c->gdepth > 0 && IS_SPE(c,QSE_T(')'))))

	if (REACHED_END(c))
	{
		qse_rex_node_t* nop = newnopnode (c);	
		if (nop == QSE_NULL) return QSE_NULL;
		nop->occ.min = 1; nop->occ.max = 1;
		pair->head = nop; pair->tail = nop;
	}
	else
	{
		pair->head = QSE_NULL; pair->tail = QSE_NULL;

		do
		{
			qse_rex_node_t* atom = comp_atom (c);
			if (atom == QSE_NULL) return QSE_NULL;

			if (atom->occ.min <= 0)
			{
			#if 0
				if (atom->occ.max >= OCC_MAX)
				{
					/*    
					 * +-----------next--+
					 * v                 | 
					 * BR --alter----> ORG(atom)
					 * | 
					 * +----next------------------->
					 *    
					 */
					atom = zero_or_more (c, atom);
				}
				else
				{
			#endif
					/*
					 * Given an atom, enclose it with a
					 * pseudogroup head and a psuedogroup 
					 * tail. the head is followed by a 
					 * branch that conntects to the tail 
					 * and the atom given. The atom given
					 * gets connected to the tail.
					 *   Head -> BR        -> Tail
					 *        -> ORG(atom) -> Tail
					 */
					atom = pseudo_group (c, atom);
			#if 0
				}
			#endif
				if (atom == QSE_NULL) return QSE_NULL;
			}
	
			if (pair->tail == QSE_NULL) 
			{
				QSE_ASSERT (pair->head == QSE_NULL);
				pair->head = atom;
			}
			else pair->tail->next = atom;
			pair->tail = atom;
		}
		while (!REACHED_END(c));
	}

	return pair->head;
#undef REACHED_END
}

static qse_rex_node_t* comp_branches (comp_t* c, qse_rex_node_t* ge)
{
	qse_rex_node_t* left, * right, * tmp;
	pair_t xpair;

	left = comp_branch (c, &xpair);
	if (left == QSE_NULL) return QSE_NULL;
	xpair.tail->next = ge;

	while (IS_SPE(c,QSE_T('|')))
	{
		if (getc_esc(c) <= -1) return QSE_NULL;
		
		right = comp_branch (c, &xpair);
		if (right == QSE_NULL) return QSE_NULL;

		xpair.tail->next = ge;

		tmp = newbranchnode (c, left, right);
		if (tmp == QSE_NULL) return QSE_NULL;

		left = tmp;
	} 

	return left;
}

qse_rex_node_t* qse_rex_comp (
	qse_rex_t* rex, const qse_char_t* ptr, qse_size_t len)
{
	comp_t c;
	qse_rex_node_t* end, * body;

	c.rex = rex;
	c.re.ptr = ptr;
	c.re.len = len;	

	c.ptr = ptr;
	c.end = ptr + len;

	c.c.value = QSE_CHAR_EOF;

	c.gdepth = 0;
	c.start = QSE_NULL;

	/* read the first character */
	if (getc_esc(&c) <= -1) return QSE_NULL;

	c.start = newstartnode (&c);
	if (c.start == QSE_NULL) return QSE_NULL;

	end = newendnode (&c);
	if (end == QSE_NULL)
	{
		freenode (c.start, c.rex->mmgr);
		return QSE_NULL;
	}

	body = comp_branches (&c, end);
	if (body == QSE_NULL) 
	{
		freeallnodes (c.start);
		return QSE_NULL;
	}

	c.start->next = body;
	if (rex->code != QSE_NULL) freeallnodes (rex->code);
	rex->code = c.start;

	return rex->code;
}

static void freegroupstackmembers (group_t* gs, qse_mmgr_t* mmgr)
{
	while (gs != QSE_NULL)
	{
		group_t* next = gs->next;
		QSE_MMGR_FREE (mmgr, gs);
		gs = next;
	}
}

static void freegroupstack (group_t* gs, qse_mmgr_t* mmgr)
{
	QSE_ASSERT (gs != QSE_NULL);
	QSE_ASSERTX (gs->node == QSE_NULL, 
		"The head of a group stack must point to QSE_NULL for management purpose.");

	freegroupstackmembers (gs, mmgr);
}

static void refupgroupstack (group_t* gs)
{
	if (gs != QSE_NULL)
	{
		QSE_ASSERTX (gs->node == QSE_NULL, 
			"The head of a group stack must point to QSE_NULL for management purpose.");
		gs->occ++;
	}
}

static void refdowngroupstack (group_t* gs, qse_mmgr_t* mmgr)
{
	if (gs != QSE_NULL)
	{
		QSE_ASSERTX (gs->node == QSE_NULL, 
			"The head of a group stack must point to QSE_NULL for management purpose.");
		if (--gs->occ <= 0)
		{
			freegroupstack (gs, mmgr);
		}
	}
}

static group_t* dupgroupstackmembers (exec_t* e, group_t* g)
{
	group_t* yg, * xg = QSE_NULL;

	QSE_ASSERT (g != QSE_NULL);

	if (g->next != QSE_NULL) 
	{
		/* TODO: make it non recursive or 
		 *       implement stack overflow protection */
		xg = dupgroupstackmembers (e, g->next);
		if (xg == QSE_NULL) return QSE_NULL;
	}

	yg = (group_t*) QSE_MMGR_ALLOC (e->rex->mmgr, QSE_SIZEOF(*yg));
	if (yg == QSE_NULL)
	{
		if (xg != QSE_NULL) freegroupstack (xg, e->rex->mmgr);
		e->rex->errnum = QSE_REX_ENOMEM;
		return QSE_NULL;
	}

	QSE_MEMCPY (yg, g, QSE_SIZEOF(*yg));
	yg->next = xg;

	return yg;
}

static group_t* dupgroupstack (exec_t* e, group_t* gs)
{
	group_t* head;

	QSE_ASSERT (gs != QSE_NULL);
	QSE_ASSERTX (gs->node == QSE_NULL, 
		"The head of a group stack must point to QSE_NULL for management purpose.");

	head = dupgroupstackmembers (e, gs);
	if (head == QSE_NULL) return QSE_NULL;

	QSE_ASSERTX (
		head->node == QSE_NULL && 
		head->node == gs->node && 
		head->occ == gs->occ,
		"The duplicated stack head must not be corrupted"
	);

	/* reset the reference count of a duplicated stack */
	head->occ = 0;
	return head;
}

/* push 'gn' to the group stack 'gs'.
 * if dup is non-zero, the group stack is duplicated and 'gn' is pushed to 
 * its top */
static group_t* __groupstackpush (
	exec_t* e, group_t* gs, qse_rex_node_t* gn, int dup)
{
	group_t* head, * elem;

	QSE_ASSERT (gn->id == QSE_REX_NODE_GROUP);

	if (gs == QSE_NULL)
	{
		/* gn is the first group pushed. no stack yet.
		 * create the head to store management info. */
		head = (group_t*) QSE_MMGR_ALLOC (e->rex->mmgr, QSE_SIZEOF(*head));
		if (head == QSE_NULL)
		{
			e->rex->errnum = QSE_REX_ENOMEM;
			return QSE_NULL;
		}

		/* the head does not point to any group node. */
		head->node = QSE_NULL;
		/* the occ field is used for reference counting. 
		 * refupgroupstack and refdowngroupstack update it. */
		head->occ = 0;
		/* the head links to the first actual group */
		head->next = QSE_NULL;	
	}
	else 
	{
		if (dup)
		{
			/* duplicate existing stack */
			head = dupgroupstack (e, gs);
			if (head == QSE_NULL) return QSE_NULL;
		}
		else
		{
			head = gs;
		}
	}

	/* create a new stack element */
	elem = (group_t*) QSE_MMGR_ALLOC (e->rex->mmgr, QSE_SIZEOF(*elem));
	if (elem == QSE_NULL)
	{
		/* rollback */
		if (gs == QSE_NULL) 
			QSE_MMGR_FREE (e->rex->mmgr, head);
		else if (dup) 
			freegroupstack (head, e->rex->mmgr);

		e->rex->errnum = QSE_REX_ENOMEM;
		return QSE_NULL;
	}

	/* initialize the element */
	elem->node = gn;
	elem->occ = 0;

	/* make it the top */
	elem->next = head->next;
	head->next = elem;

	return head;
}

#define dupgroupstackpush(e,gs,gn) __groupstackpush(e,gs,gn,1)
#define groupstackpush(e,gs,gn) __groupstackpush(e,gs,gn,0)

/* duplidate a group stack excluding the top data element */
static group_t* dupgroupstackpop (exec_t* e, group_t* gs)
{
	group_t* dupg, * head;

	QSE_ASSERT (gs != QSE_NULL);
	QSE_ASSERTX (gs->node == QSE_NULL, 
		"The head of a group stack must point to QSE_NULL for management purpose.");
	QSE_ASSERTX (gs->next != QSE_NULL && gs->next->next != QSE_NULL, 
		"dupgroupstackpop() needs at least two data elements");

	dupg = dupgroupstackmembers (e, gs->next->next);
	if (dupg == QSE_NULL) return QSE_NULL;

	head = (group_t*) QSE_MMGR_ALLOC (e->rex->mmgr, QSE_SIZEOF(*head));
	if (head == QSE_NULL)
	{
		if (dupg != QSE_NULL) freegroupstackmembers (dupg, e->rex->mmgr);
		e->rex->errnum = QSE_REX_ENOMEM;
		return QSE_NULL;
	}

	head->node = QSE_NULL;
	head->occ = 0;
	head->next = dupg;

	return head;
}

static group_t* groupstackpop (exec_t* e, group_t* gs)
{
	group_t* top;

	QSE_ASSERT (gs != QSE_NULL);
	QSE_ASSERTX (gs->node == QSE_NULL, 
		"The head of a group stack must point to QSE_NULL for management purpose.");
	QSE_ASSERTX (gs->next != QSE_NULL && gs->next->next != QSE_NULL, 
		"groupstackpop() needs at least two data elements");


	top = gs->next;
	gs->next = top->next;

	QSE_MMGR_FREE (e->rex->mmgr, top);	
	return gs;
}

static int addsimplecand (
	exec_t* e, group_t* group, qse_rex_node_t* node, 
	qse_size_t occ, const qse_char_t* mptr)
{
	cand_t cand;

	QSE_ASSERT (
		node->id == QSE_REX_NODE_NOP ||
		node->id == QSE_REX_NODE_BOL ||
		node->id == QSE_REX_NODE_EOL ||
		node->id == QSE_REX_NODE_ANY ||
		node->id == QSE_REX_NODE_CHAR ||
		node->id == QSE_REX_NODE_CSET
	);

	cand.node = node;
	cand.occ = occ;
	cand.group = group;
	cand.mptr = mptr;

	if (qse_lda_search (
		&e->cand.set[e->cand.pending],
		0, &cand, 1) != QSE_LDA_NIL)
	{
		/* exclude any existing entries in the array.
		 * see comp_cand() for the equality test used.
		 * note this linear search may be a performance bottle neck	
		 * if the arrary grows large. not so sure if it should be
		 * switched to a different data structure such as a hash table.
		 * the problem is that most practical regular expressions
		 * won't have many candidates for a particular match point.
		 * so i'm a bit skeptical about data struct switching.
		 */
		return 0;
	}

	if (qse_lda_insert (
		&e->cand.set[e->cand.pending],
		QSE_LDA_SIZE(&e->cand.set[e->cand.pending]),
		&cand, 1) == QSE_LDA_NIL)
	{
		e->rex->errnum = QSE_REX_ENOMEM;
		return -1;
	}

	/* the reference must be decremented by the freeer */
	refupgroupstack (group);
	return 0;
}

/* addcands() function add a candicate from candnode.
 * if candnode is not a simple node, it traverses further
 * until it reaches a simple node. prevnode is the last
 * GROUPEND node visited during traversal. If no GROUPEND
 * is visited yet, it can be any starting node */
static int addcands (
	exec_t* e, group_t* group, qse_rex_node_t* prevnode,
	qse_rex_node_t* candnode, const qse_char_t* mptr)
{
	qse_rex_node_t* curcand = candnode;

warpback:

	/* skip all NOP nodes */
	while (curcand != QSE_NULL && curcand->id == QSE_REX_NODE_NOP) 
		curcand = curcand->next;

	/* nothing to add */
	if (curcand == QSE_NULL) return 0;

	switch (curcand->id)
	{
		case QSE_REX_NODE_END:
		{
			if (e->matchend == QSE_NULL || mptr >= e->matchend)
				e->matchend = mptr;
			e->nmatches++;
			break;
		}

		case QSE_REX_NODE_BRANCH:
		{
			group_t* gx = group;
			int n;

			if (group != QSE_NULL)
			{
				gx = dupgroupstack (e, group);
				if (gx == QSE_NULL) return -1;
			}

			refupgroupstack (gx);
			n = addcands (e, gx, 
				prevnode, curcand->u.b.alter, mptr);
			refdowngroupstack (gx, e->rex->mmgr);
			if (n <= -1) return -1;
	
			curcand = curcand->next;
			goto warpback;
		}

		case QSE_REX_NODE_GROUP:
		{
			qse_rex_node_t* front;
			group_t* gx;

		#ifdef XTRA_DEBUG
			qse_printf (QSE_T("DEBUG: GROUP %p(pseudo=%d) PREV %p\n"),
				curcand, curcand->u.g.pseudo, prevnode);
		#endif
			if (curcand->u.g.pseudo) 
			{
				curcand = curcand->u.g.head;
				goto warpback;
			}

			/* skip all NOP nodes */
			front = curcand->u.g.head;

			while (front->id == QSE_REX_NODE_NOP) 
				front = front->next;
			if (front->id == QSE_REX_NODE_GROUPEND) 
			{
				/* if GROUPEND is reached, the group
				 * is empty. jump to the next node
				 * regardless of its occurrence. 
				 * however, this will never be reached 
				 * as it has been removed in comp() */
				curcand = curcand->next;
				goto warpback;
			}

			gx = groupstackpush (e, group, curcand);
			if (gx == QSE_NULL) return -1;

			/* add the first node in the group to 
			 * the candidate array */
			group = gx;
			curcand = front;
			goto warpback;
		}

		case QSE_REX_NODE_GROUPEND:
		{
			int n;
			group_t* top;
			qse_rex_node_t* node;
			qse_size_t occ;

		#ifdef XTRA_DEBUG
			qse_printf (QSE_T("DEBUG: GROUPEND %p(pseudo=%d) PREV %p\n"), 
				curcand, curcand->u.ge.pseudo, prevnode);
		#endif

			if (curcand->u.ge.pseudo) 
			{
				curcand = curcand->u.ge.group->next;	
				goto warpback;
			}

			QSE_ASSERTX (
				group != QSE_NULL && group->next != QSE_NULL, 
				"GROUPEND must be paired up with GROUP");

			if (prevnode == curcand) 
			{
				/* consider a pattern like (x*)*.
				 * when GROUPEND is reached, an 'if' block 
				 * below tries to add the first node 
				 * (node->u.g.head) in the group again. 
				 * however, it('x') is optional, a possible 
				 * path reach GROUPEND directly without 
				 * adding a candidate. this check is needed to 
				 * avoid the infinite loop, which otherwise is 
				 * not avoidable. */
				break;
			}
	
			top = group->next;
			top->occ++;

			occ = top->occ;
			node = top->node;
			QSE_ASSERTX (node == curcand->u.ge.group, 
				"The GROUP node in the group stack must be the one pairing up with the GROUPEND node."
			);
	
			if (occ >= node->occ.min)
			{
				group_t* gx;
	
				/* the lower bound has been met. 
				 * for a pattern (abc){3,4}, 'abc' has been 
				 * repeated 3 times. in this case, the next 
				 * node can be added to the candiate array.
				 * it is actually a branch case. move on. */
	
				if (top->next == QSE_NULL)
				{
					/* only one element in the stack.
					 * falls back to QSE_NULL regardless 
					 * of the need to reuse it */
					gx = QSE_NULL;
				}
				else if (occ < node->occ.max)
				{
					/* check if the group will be repeated.
					 * if so, duplicate the group stack 
					 * excluding the top. it goes along a 
					 * different path and hence requires  
					 * duplication. */

					gx = dupgroupstackpop (e, group);
					if (gx == QSE_NULL) return -1;
				}
				else
				{
					/* reuse the group stack. pop the top 
					 * data element off the stack */

					gx = groupstackpop (e, group);

					/* this function always succeeds and
					 * returns the same head */
					QSE_ASSERT (gx == group);
				}
	
				refupgroupstack (gx);

				if (prevnode != QSE_NULL && 
				    prevnode->id == QSE_REX_NODE_GROUPEND)
					n = addcands (e, gx, prevnode, node->next, mptr);
				else
					n = addcands (e, gx, curcand, node->next, mptr);

				refdowngroupstack (gx, e->rex->mmgr);
				if (n <= -1) return -1;
			}

			if (occ < node->occ.max)
			{
				/* repeat itself. */
				prevnode = curcand;
				curcand = node->u.g.head;
				goto warpback;
			}

			break;
		}

		default:
		{
			int n;

			if (group) refupgroupstack (group);
			n = addsimplecand (e, group, curcand, 1, mptr);
			if (group) refdowngroupstack (group, e->rex->mmgr);

			if (n <= -1) return -1;
			break;
		}
	}

	return 0;
}

static int charset_matched (exec_t* e, qse_rex_node_t* node, qse_char_t c)
{
	const qse_char_t* ptr, * end;
	int matched = 0;

	QSE_ASSERT (node->u.cset.member != QSE_NULL);

	ptr = QSE_STR_PTR (node->u.cset.member);
	end = ptr + QSE_STR_LEN (node->u.cset.member);

	while (ptr < end && !matched)
	{
		switch (*ptr)
		{
			case QSE_REX_CSET_CHAR:
			{
				ptr++;

				if (e->rex->option & QSE_REX_IGNORECASE)
				{
					if (QSE_TOUPPER(c) == QSE_TOUPPER(*ptr)) matched = !0;
				}
				else
				{
					if (c == *ptr) matched = !0;
				}
				break;
			}
				
			case QSE_REX_CSET_RANGE:
			{
				qse_char_t c1, c2;

				if (e->rex->option & QSE_REX_IGNORECASE)
				{
					qse_char_t c3;
					ptr++; c1 = QSE_TOUPPER(*ptr);
					ptr++; c2 = QSE_TOUPPER(*ptr);
					c3 = QSE_TOUPPER(c);
					if (c3 >= c1 && c3 <= c2) matched = !0;
				}
				else
				{
					c1 = *++ptr; c2 = *++ptr;
					if (c >= c1 && c <= c2) matched = !0;
				}
				break;
			}
				
			case QSE_REX_CSET_CLASS:
			{
				qse_char_t c1;

				c1 = *++ptr;
				QSE_ASSERT (c1 < QSE_COUNTOF(ccinfo));
				if (ccinfo[c1].func(e,c)) matched = !0;
			
				break;
			}

			default:
			{
				QSE_ASSERTX (0, 
					"SHOUL NEVER HAPPEN - membership code for a character set must be one of QSE_REX_CSET_CHAR, QSE_REX_CSET_RANGE, QSE_REX_CSET_CLASS");

				/* return no match if this part is reached.
				 * however, something is totally wrong if it
				 * happens. */
				return 0;
			}
		}

		ptr++;
	}

	if (node->u.cset.negated) matched = !matched;
	return matched;
}

static qse_lda_walk_t walk_cands_for_match (
	qse_lda_t* lda, qse_size_t index, void* ctx)
{
	exec_t* e = (exec_t*)ctx;	
	cand_t* cand = QSE_LDA_DPTR(lda,index);
	qse_rex_node_t* node = cand->node;
	const qse_char_t* nmptr = QSE_NULL;

	switch (node->id)
	{
		case QSE_REX_NODE_BOL:
			if (cand->mptr == e->str.ptr) 
			{
				/* the next match pointer remains 
				 * the same as ^ matches a position,
				 * not a character. */
				nmptr = cand->mptr;
			#ifdef XTRA_DEBUG
				qse_printf (QSE_T("DEBUG: matched <^>\n"));
			#endif
			}
			break;

		case QSE_REX_NODE_EOL:
			if (cand->mptr >= e->str.end) 
			{
				/* the next match pointer remains 
				 * the same as $ matches a position,
				 * not a character. */
				nmptr = cand->mptr;
			#ifdef XTRA_DEBUG
				qse_printf (QSE_T("DEBUG: matched <$>\n"));
			#endif
			}
			break;

		case QSE_REX_NODE_ANY:
			if (cand->mptr < e->sub.end) 
			{
				/* advance the match pointer to the
				 * next chracter.*/
				nmptr = cand->mptr + 1;
			#ifdef XTRA_DEBUG
				qse_printf (QSE_T("DEBUG: matched <.>\n"));
			#endif
			}
			break;

		case QSE_REX_NODE_CHAR:	
		{
			if (cand->mptr < e->sub.end)
			{
				int equal;

				equal = (e->rex->option & QSE_REX_IGNORECASE)?
					(QSE_TOUPPER(node->u.c) == QSE_TOUPPER(*cand->mptr)):
					(node->u.c == *cand->mptr) ;

				if (equal)
				{
					/* advance the match pointer to the
					 * next chracter.*/
					nmptr = cand->mptr + 1;
				}
			#ifdef XTRA_DEBUG
				qse_printf (QSE_T("DEBUG: matched %c\n"), node->u.c); 
			#endif
			}
			break;
		}

		case QSE_REX_NODE_CSET:
		{
			if (cand->mptr < e->sub.end &&
			    charset_matched(e, node, *cand->mptr))
			{
				/* advance the match pointer 
				 * to the next chracter.*/
				nmptr = cand->mptr + 1;
			}

			break;
		}

		default:
		{
			QSE_ASSERTX (0, 
				"SHOULD NEVER HAPPEN - node ID must be one of QSE_REX_NODE_BOL, QSE_REX_NODE_EOL, QSE_REX_NODE_ANY, QSE_REX_NODE_CHAR, QSE_REX_NODE_CSET, QSE_REX_NODE_NOP");
			break;
		}
	}

	if (nmptr != QSE_NULL)
	{
		int n;

		if (cand->occ >= node->occ.min)
		{
			group_t* gx;

			if (cand->occ < node->occ.max && cand->group != QSE_NULL)
			{
				gx = dupgroupstack (e, cand->group);
				if (gx == QSE_NULL) return QSE_LDA_WALK_STOP;
			}
			else gx = cand->group;

			/* move on to the next candidate */
			refupgroupstack (gx);
			n = addcands (e, gx, node, node->next, nmptr);
			refdowngroupstack (gx, e->rex->mmgr);

			if (n <= -1) return QSE_LDA_WALK_STOP;
		}

		if (cand->occ < node->occ.max)
		{
			/* repeat itself more */
			refupgroupstack (cand->group);
			n = addsimplecand (
				e, cand->group, 
				node, cand->occ + 1, nmptr);
			refdowngroupstack (cand->group, e->rex->mmgr);

			if (n <= -1) return QSE_LDA_WALK_STOP;
		}
	}

	return QSE_LDA_WALK_FORWARD;
}

static int exec (exec_t* e)
{
	int n;

	e->nmatches = 0;
	e->matchend = QSE_NULL;

	e->cand.pending = 0;
	e->cand.active = 1;

	/* empty the pending set to collect the initial candidates */
	qse_lda_clear (&e->cand.set[e->cand.pending]); 

	/* the first node must be the START node */
	QSE_ASSERT (e->rex->code->id == QSE_REX_NODE_START);

	/* collect an initial set of candidates into the pending set */
	n = addcands (
		e,                  /* execution structure */
		QSE_NULL,           /* doesn't belong to any groups yet */
		e->rex->code,       /* dummy previous node, the start node */
		e->rex->code->next, /* start from the second node */
		e->sub.ptr          /* current match pointer */
	);
	if (n <= -1) return -1;

	do
	{
		qse_size_t ncands_active;

		/* swap the pending and active set indices.
		 * the pending set becomes active after which the match()
		 * function tries each candidate in it. New candidates
		 * are added into the pending set which will become active
		 * later when the loop reaches here again */
		int tmp = e->cand.pending;
		e->cand.pending = e->cand.active;
		e->cand.active = tmp;

		ncands_active = QSE_LDA_SIZE(&e->cand.set[e->cand.active]);
		if (ncands_active <= 0)
		{
			/* we can't go on with no candidates in the 
			 * active set. */
			break;
		}

		/* clear the pending set */
		qse_lda_clear (&e->cand.set[e->cand.pending]); 

#ifdef XTRA_DEBUG
		{
			int i;
			qse_printf (QSE_T("SET="));
			for (i = 0; i < ncands_active; i++)
			{
				cand_t* cand = QSE_LDA_DPTR(&e->cand.set[e->cand.active],i);
				qse_rex_node_t* node = cand->node;

				if (node->id == QSE_REX_NODE_CHAR)
					qse_printf (QSE_T("%c "), node->u.c);
				else if (node->id == QSE_REX_NODE_ANY)
					qse_printf (QSE_T(". "), node->u.c);
				else if (node->id == QSE_REX_NODE_BOL)
					qse_printf (QSE_T("^ "));
				else if (node->id == QSE_REX_NODE_EOL)
					qse_printf (QSE_T("$ "));
			}
			qse_printf (QSE_T("\n"));
		}
#endif

		if (qse_lda_walk (
			&e->cand.set[e->cand.active],
			walk_cands_for_match, e) != ncands_active) 
		{
			/* if the number of walks is different the number of
			 * candidates, traversal must have been aborted for
			 * an error. */
			return -1; 
		}
	}
	while (1);

#ifdef XTRA_DEBUG
	if (e->nmatches > 0)
	{
		qse_printf (QSE_T("MATCH: %d [%.*s]\n"), 
			(int)(e->matchend - e->sub.ptr), 
			(int)(e->matchend - e->sub.ptr), e->sub.ptr);
	}
	qse_printf (QSE_T("TOTAL MATCHES FOUND... %d\n"), e->nmatches);
#endif

	return (e->nmatches > 0)? 1: 0;
}

static void refdowngroupstack_incand (qse_lda_t* lda, void* dptr, qse_size_t dlen)
{
	QSE_ASSERT (dlen == 1);
	refdowngroupstack (((cand_t*)dptr)->group, lda->mmgr);
}

static int comp_cand (qse_lda_t* lda,
	const void* dptr1, qse_size_t dlen1,
	const void* dptr2, qse_size_t dlen2)
{
	cand_t* c1 = (cand_t*)dptr1;
	cand_t* c2 = (cand_t*)dptr2;
/*qse_printf (QSE_T("%p(%d) %p(%d), %p %p, %d %d\n"), c1->node,c1->node->id, c2->node,c1->node->id, c1->mptr, c2->mptr, (int)c1->occ, (int)c2->occ);*/
	return (c1->node == c2->node && 
	        c1->mptr == c2->mptr &&
	        c1->occ == c2->occ)? 0: 1;
}

static int init_exec_dds (exec_t* e, qse_mmgr_t* mmgr)
{
	/* initializes dynamic data structures */
	if (qse_lda_init (&e->cand.set[0], mmgr, 100) <= -1)
	{
		e->rex->errnum = QSE_REX_ENOMEM;
		return -1;
	}
	if (qse_lda_init (&e->cand.set[1], mmgr, 100) <= -1)
	{
		e->rex->errnum = QSE_REX_ENOMEM;
		qse_lda_fini (&e->cand.set[0]);
		return -1;
	}

	qse_lda_setscale (&e->cand.set[0], QSE_SIZEOF(cand_t));
	qse_lda_setscale (&e->cand.set[1], QSE_SIZEOF(cand_t));

	qse_lda_setcopier (&e->cand.set[0], QSE_LDA_COPIER_INLINE);
	qse_lda_setcopier (&e->cand.set[1], QSE_LDA_COPIER_INLINE);

	qse_lda_setfreeer (&e->cand.set[0], refdowngroupstack_incand);
	qse_lda_setfreeer (&e->cand.set[1], refdowngroupstack_incand);

	qse_lda_setcomper (&e->cand.set[0], comp_cand);
	qse_lda_setcomper (&e->cand.set[1], comp_cand);

	return 0;
}

static void fini_exec_dds (exec_t* e)
{
	qse_lda_fini (&e->cand.set[1]);
	qse_lda_fini (&e->cand.set[0]);
}

int qse_rex_exec (
	qse_rex_t* rex, const qse_cstr_t* str, 
	const qse_cstr_t* substr, qse_cstr_t* matstr)
{
	exec_t e;
	int n = 0;

	if (rex->code == QSE_NULL)
	{
		rex->errnum = QSE_REX_ENOCOMP;
		return -1;
	}

	QSE_MEMSET (&e, 0, QSE_SIZEOF(e));

	e.rex = rex;
	e.str.ptr = str->ptr;
	e.str.end = str->ptr + str->len;
	e.sub.ptr = substr->ptr;
	e.sub.end = substr->ptr + substr->len;

	if (init_exec_dds (&e, rex->mmgr) <= -1) return -1;

	while (e.sub.ptr <= e.sub.end)
	{
		n = exec (&e);
		if (n <= -1) 
		{
			n = -1;
			break;
		}

		if (n >= 1)
		{
			QSE_ASSERT (e.nmatches > 0);
			QSE_ASSERT (e.matchend != QSE_NULL);
			if (matstr)
			{
				matstr->ptr = e.sub.ptr;
				matstr->len = e.matchend - e.sub.ptr;
			}
			break;
		}

		e.sub.ptr++;
	}

	fini_exec_dds (&e);

	return n;
}


void* qse_buildrex (
	qse_mmgr_t* mmgr, qse_size_t depth, int option,
	const qse_char_t* ptn, qse_size_t len, qse_rex_errnum_t* errnum)
{
	qse_rex_t rex;
	qse_rex_node_t* code;

	qse_rex_init (&rex, mmgr, QSE_NULL);
	qse_rex_setoption (&rex, option);

	if (qse_rex_comp (&rex, ptn, len) == QSE_NULL)
	{
		*errnum = rex.errnum;
		qse_rex_fini (&rex);
		return QSE_NULL;
	}

	code = qse_rex_yield (&rex);

	qse_rex_fini (&rex);
	return code;
}


int qse_matchrex (
	qse_mmgr_t* mmgr, qse_size_t depth,
	void* code, int option,
	const qse_cstr_t* str, const qse_cstr_t* substr,
	qse_cstr_t* match, qse_rex_errnum_t* errnum)
{
	qse_rex_t rex;
	int n;

	qse_rex_init (&rex, mmgr, code);
	qse_rex_setoption (&rex, option);

	if ((n = qse_rex_exec (&rex, str, substr, match)) <= -1)
	{
		*errnum = rex.errnum;
		qse_rex_yield (&rex);
		qse_rex_fini (&rex);
		return -1;
	}

	qse_rex_yield (&rex);
	qse_rex_fini (&rex);

	return n;
}

void qse_freerex (qse_mmgr_t* mmgr, void* code)
{
	qse_rex_t rex;
	qse_rex_init (&rex, mmgr, code);
	qse_rex_fini (&rex);
}