Optimization for single byte encodings.

src/backend/utils/adt/like_match.c

+/*-------------------------------------------------------------------------
+ *
+ * like_match.c
+ *	  like expression handling internal code.
+ *
+ * This file is included by like.c *twice* if multibyte is enabled.
+ * This is for an optimization of single byte encodings.
+ * Before the inclusion, we need to define following macros:
+ *
+ * CHAREQ
+ * ICHAREQ
+ * NextChar
+ * CopyAdvChar
+ * MatchText (MBMatchText)
+ * MatchTextIC (MBMatchTextIC)
+ * do_like_escape (MB_do_like_escape)
+ *
+ * Copyright (c) 1996-2001, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	$Header: /cvsroot/pgsql/src/backend/utils/adt/like_match.c,v 1.1 2001/10/04 02:15:47 ishii Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/*
+**	Originally written by Rich $alz, mirror!rs, Wed Nov 26 19:03:17 EST 1986.
+**	Rich $alz is now <rsalz@bbn.com>.
+**	Special thanks to Lars Mathiesen <thorinn@diku.dk> for the LABORT code.
+**
+**	This code was shamelessly stolen from the "pql" code by myself and
+**	slightly modified :)
+**
+**	All references to the word "star" were replaced by "percent"
+**	All references to the word "wild" were replaced by "like"
+**
+**	All the nice shell RE matching stuff was replaced by just "_" and "%"
+**
+**	As I don't have a copy of the SQL standard handy I wasn't sure whether
+**	to leave in the '\' escape character handling.
+**
+**	Keith Parks. <keith@mtcc.demon.co.uk>
+**
+**	SQL92 lets you specify the escape character by saying
+**	LIKE <pattern> ESCAPE <escape character>. We are a small operation
+**	so we force you to use '\'. - ay 7/95
+**
+**	Now we have the like_escape() function that converts patterns with
+**	any specified escape character (or none at all) to the internal
+**	default escape character, which is still '\'. - tgl 9/2000
+**
+** The code is rewritten to avoid requiring null-terminated strings,
+** which in turn allows us to leave out some memcpy() operations.
+** This code should be faster and take less memory, but no promises...
+** - thomas 2000-08-06
+**
+*/
+
+
+/*--------------------
+ *	Match text and p, return LIKE_TRUE, LIKE_FALSE, or LIKE_ABORT.
+ *
+ *	LIKE_TRUE: they match
+ *	LIKE_FALSE: they don't match
+ *	LIKE_ABORT: not only don't they match, but the text is too short.
+ *
+ * If LIKE_ABORT is returned, then no suffix of the text can match the
+ * pattern either, so an upper-level % scan can stop scanning now.
+ *--------------------
+ */
+
+static int
+MatchText(unsigned char *t, int tlen, unsigned char *p, int plen)
+{
+	/* Fast path for match-everything pattern */
+	if ((plen == 1) && (*p == '%'))
+		return LIKE_TRUE;
+
+	while ((tlen > 0) && (plen > 0))
+	{
+		if (*p == '\\')
+		{
+			/* Next pattern char must match literally, whatever it is */
+			NextChar(p, plen);
+			if ((plen <= 0) || !CHAREQ(t, p))
+				return LIKE_FALSE;
+		}
+		else if (*p == '%')
+		{
+			/* %% is the same as % according to the SQL standard */
+			/* Advance past all %'s */
+			while ((plen > 0) && (*p == '%'))
+				NextChar(p, plen);
+			/* Trailing percent matches everything. */
+			if (plen <= 0)
+				return LIKE_TRUE;
+
+			/*
+			 * Otherwise, scan for a text position at which we can match
+			 * the rest of the pattern.
+			 */
+			while (tlen > 0)
+			{
+
+				/*
+				 * Optimization to prevent most recursion: don't recurse
+				 * unless first pattern char might match this text char.
+				 */
+				if (CHAREQ(t, p) || (*p == '\\') || (*p == '_'))
+				{
+					int			matched = MatchText(t, tlen, p, plen);
+
+					if (matched != LIKE_FALSE)
+						return matched; /* TRUE or ABORT */
+				}
+
+				NextChar(t, tlen);
+			}
+
+			/*
+			 * End of text with no match, so no point in trying later
+			 * places to start matching this pattern.
+			 */
+			return LIKE_ABORT;
+		}
+		else if ((*p != '_') && !CHAREQ(t, p))
+		{
+
+			/*
+			 * Not the single-character wildcard and no explicit match?
+			 * Then time to quit...
+			 */
+			return LIKE_FALSE;
+		}
+
+		NextChar(t, tlen);
+		NextChar(p, plen);
+	}
+
+	if (tlen > 0)
+		return LIKE_FALSE;		/* end of pattern, but not of text */
+
+	/* End of input string.  Do we have matching pattern remaining? */
+	while ((plen > 0) && (*p == '%'))	/* allow multiple %'s at end of
+										 * pattern */
+		NextChar(p, plen);
+	if (plen <= 0)
+		return LIKE_TRUE;
+
+	/*
+	 * End of text with no match, so no point in trying later places to
+	 * start matching this pattern.
+	 */
+	return LIKE_ABORT;
+}	/* MatchText() */
+
+/*
+ * Same as above, but ignore case
+ */
+static int
+MatchTextIC(unsigned char *t, int tlen, unsigned char *p, int plen)
+{
+	/* Fast path for match-everything pattern */
+	if ((plen == 1) && (*p == '%'))
+		return LIKE_TRUE;
+
+	while ((tlen > 0) && (plen > 0))
+	{
+		if (*p == '\\')
+		{
+			/* Next pattern char must match literally, whatever it is */
+			NextChar(p, plen);
+			if ((plen <= 0) || !ICHAREQ(t, p))
+				return LIKE_FALSE;
+		}
+		else if (*p == '%')
+		{
+			/* %% is the same as % according to the SQL standard */
+			/* Advance past all %'s */
+			while ((plen > 0) && (*p == '%'))
+				NextChar(p, plen);
+			/* Trailing percent matches everything. */
+			if (plen <= 0)
+				return LIKE_TRUE;
+
+			/*
+			 * Otherwise, scan for a text position at which we can match
+			 * the rest of the pattern.
+			 */
+			while (tlen > 0)
+			{
+
+				/*
+				 * Optimization to prevent most recursion: don't recurse
+				 * unless first pattern char might match this text char.
+				 */
+				if (ICHAREQ(t, p) || (*p == '\\') || (*p == '_'))
+				{
+					int			matched = MatchTextIC(t, tlen, p, plen);
+
+					if (matched != LIKE_FALSE)
+						return matched; /* TRUE or ABORT */
+				}
+
+				NextChar(t, tlen);
+			}
+
+			/*
+			 * End of text with no match, so no point in trying later
+			 * places to start matching this pattern.
+			 */
+			return LIKE_ABORT;
+		}
+		else if ((*p != '_') && !ICHAREQ(t, p))
+		{
+
+			/*
+			 * Not the single-character wildcard and no explicit match?
+			 * Then time to quit...
+			 */
+			return LIKE_FALSE;
+		}
+
+		NextChar(t, tlen);
+		NextChar(p, plen);
+	}
+
+	if (tlen > 0)
+		return LIKE_FALSE;		/* end of pattern, but not of text */
+
+	/* End of input string.  Do we have matching pattern remaining? */
+	while ((plen > 0) && (*p == '%'))	/* allow multiple %'s at end of
+										 * pattern */
+		NextChar(p, plen);
+	if (plen <= 0)
+		return LIKE_TRUE;
+
+	/*
+	 * End of text with no match, so no point in trying later places to
+	 * start matching this pattern.
+	 */
+	return LIKE_ABORT;
+}	/* MatchTextIC() */
+
+/*
+ * like_escape() --- given a pattern and an ESCAPE string,
+ * convert the pattern to use Postgres' standard backslash escape convention.
+ */
+static text *
+do_like_escape(text *pat, text *esc)
+{
+	text	   *result;
+	unsigned char *p,
+			   *e,
+			   *r;
+	int			plen,
+				elen;
+	bool		afterescape;
+
+	p = VARDATA(pat);
+	plen = (VARSIZE(pat) - VARHDRSZ);
+	e = VARDATA(esc);
+	elen = (VARSIZE(esc) - VARHDRSZ);
+
+	/*
+	 * Worst-case pattern growth is 2x --- unlikely, but it's hardly worth
+	 * trying to calculate the size more accurately than that.
+	 */
+	result = (text *) palloc(plen * 2 + VARHDRSZ);
+	r = VARDATA(result);
+
+	if (elen == 0)
+	{
+
+		/*
+		 * No escape character is wanted.  Double any backslashes in the
+		 * pattern to make them act like ordinary characters.
+		 */
+		while (plen > 0)
+		{
+			if (*p == '\\')
+				*r++ = '\\';
+			CopyAdvChar(r, p, plen);
+		}
+	}
+	else
+	{
+
+		/*
+		 * The specified escape must be only a single character.
+		 */
+		NextChar(e, elen);
+		if (elen != 0)
+			elog(ERROR, "ESCAPE string must be empty or one character");
+		e = VARDATA(esc);
+
+		/*
+		 * If specified escape is '\', just copy the pattern as-is.
+		 */
+		if (*e == '\\')
+		{
+			memcpy(result, pat, VARSIZE(pat));
+			return result;
+		}
+
+		/*
+		 * Otherwise, convert occurrences of the specified escape
+		 * character to '\', and double occurrences of '\' --- unless they
+		 * immediately follow an escape character!
+		 */
+		afterescape = false;
+		while (plen > 0)
+		{
+			if (CHAREQ(p, e) && !afterescape)
+			{
+				*r++ = '\\';
+				NextChar(p, plen);
+				afterescape = true;
+			}
+			else if (*p == '\\')
+			{
+				*r++ = '\\';
+				if (!afterescape)
+					*r++ = '\\';
+				NextChar(p, plen);
+				afterescape = false;
+			}
+			else
+			{
+				CopyAdvChar(r, p, plen);
+				afterescape = false;
+			}
+		}
+	}
+
+	VARATT_SIZEP(result) = r - ((unsigned char *) result);
+
+	return result;
+}