Per this discussion, here's a patch to implement both levenshtein() and

metaphone() in a contrib. There seem to be a fair number of different
approaches to both of these algorithms. I used the simplest case for
levenshtein which has a cost  of 1 for any character insertion, deletion, or
substitution. For metaphone, I adapted the same code from CPAN that the PHP
folks did.

A couple of questions:
1. Does it make sense to fold the soundex contrib together with this one?

2. I was debating trying to add multibyte support to levenshtein (it would
make no sense at all for metaphone), but a quick search through the contrib
directory found no hits on the word MULTIBYTE. Should worry about adding
multibyte support to levenshtein()?

Joe Conway

contrib/README

@@ -55,6 +55,10 @@ fulltextindex -
 	Full text indexing using triggers
 	by Maarten Boekhold <maartenb@dutepp0.et.tudelft.nl>
 
+fuzzystrmatch -
+	Levenshtein and Metaphone fuzzy string matching
+	by Joe Conway <joseph.conway@home.com>
+
 intarray -
 	Index support for arrays of int4, using GiST
 	by Teodor Sigaev <teodor@stack.net> and Oleg Bartunov

contrib/fuzzystrmatch/Makefile

+subdir = contrib/fuzzystrmatch
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+
+# override libdir to install shlib in contrib not main directory
+libdir := $(libdir)/contrib
+
+# shared library parameters
+NAME= fuzzystrmatch
+SO_MAJOR_VERSION= 0
+SO_MINOR_VERSION= 1
+
+override CPPFLAGS := -I$(srcdir)/src/include $(CPPFLAGS)
+
+OBJS= fuzzystrmatch.o
+
+all: all-lib $(NAME).sql
+
+# Shared library stuff
+include $(top_srcdir)/src/Makefile.shlib
+
+
+$(NAME).sql: $(NAME).sql.in
+	sed -e 's:MODULE_PATHNAME:$(libdir)/$(shlib):g' < $< > $@
+
+install: all installdirs install-lib
+
+installdirs:
+	$(mkinstalldirs) $(DESTDIR)$(libdir)
+
+uninstall: uninstall-lib
+
+clean distclean maintainer-clean: clean-lib
+	rm -f $(OBJS) $(NAME).sql
+
+depend dep:
+	$(CC) -MM $(CFLAGS) *.c >depend
+
+ifeq (depend,$(wildcard depend))
+include depend
+endif

contrib/fuzzystrmatch/README.fuzzystrmatch

+/*
+ * fuzzystrmatch.c
+ *
+ * Functions for "fuzzy" comparison of strings
+ *
+ * Copyright (c) Joseph Conway <joseph.conway@home.com>, 2001;
+ *
+ * levenshtein()
+ * -------------
+ * Written based on a description of the algorithm by Michael Gilleland
+ * found at http://www.merriampark.com/ld.htm
+ * Also looked at levenshtein.c in the PHP 4.0.6 distribution for
+ * inspiration.
+ *
+ * metaphone()
+ * -----------
+ * Modified for PostgreSQL by Joe Conway.
+ * Based on CPAN's "Text-Metaphone-1.96" by Michael G Schwern <schwern@pobox.com>
+ * Code slightly modified for use as PostgreSQL function (palloc, elog, etc).
+ * Metaphone was originally created by Lawrence Philips and presented in article
+ * in "Computer Language" December 1990 issue.
+ *
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ * 
+ * IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+
+
+Version 0.1 (3 August, 2001):
+  Functions to calculate the degree to which two strings match in a "fuzzy" way
+  Tested under Linux (Red Hat 6.2 and 7.0) and PostgreSQL 7.2devel
+
+Release Notes:
+
+  Version 0.1
+    - initial release    
+
+Installation:
+  Place these files in a directory called 'fuzzystrmatch' under 'contrib' in the PostgreSQL source tree. Then run:
+
+    make
+    make install
+
+  You can use fuzzystrmatch.sql to create the functions in your database of choice, e.g.
+
+    psql -U postgres template1 < fuzzystrmatch.sql
+
+  installs following functions into database template1:
+
+     levenshtein() - calculates the levenshtein distance between two strings
+     metaphone() - calculates the metaphone code of an input string
+
+Documentation
+==================================================================
+Name
+
+levenshtein -- calculates the levenshtein distance between two strings
+
+Synopsis
+
+levenshtein(text source, text target)
+
+Inputs
+
+  source
+    any text string, 255 characters max, NOT NULL
+
+  target
+    any text string, 255 characters max, NOT NULL
+
+Outputs
+
+  Returns int
+
+Example usage
+
+  select levenshtein('GUMBO','GAMBOL');
+
+==================================================================
+Name
+
+metaphone -- calculates the metaphone code of an input string
+
+Synopsis
+
+metaphone(text source, int max_output_length)
+
+Inputs
+
+  source
+    any text string, 255 characters max, NOT NULL
+
+  max_output_length
+    maximum length of the output metaphone code; if longer, the output
+    is truncated to this length
+
+Outputs
+
+  Returns text
+
+Example usage
+
+  select metaphone('GUMBO',4);
+
+==================================================================
+-- Joe Conway
+

contrib/fuzzystrmatch/fuzzystrmatch.c

+/*
+ * fuzzystrmatch.c
+ *
+ * Functions for "fuzzy" comparison of strings
+ *
+ * Copyright (c) Joseph Conway <joseph.conway@home.com>, 2001;
+ *
+ * levenshtein()
+ * -------------
+ * Written based on a description of the algorithm by Michael Gilleland
+ * found at http://www.merriampark.com/ld.htm
+ * Also looked at levenshtein.c in the PHP 4.0.6 distribution for
+ * inspiration.
+ *
+ * metaphone()
+ * -----------
+ * Modified for PostgreSQL by Joe Conway.
+ * Based on CPAN's "Text-Metaphone-1.96" by Michael G Schwern <schwern@pobox.com>
+ * Code slightly modified for use as PostgreSQL function (palloc, elog, etc).
+ * Metaphone was originally created by Lawrence Philips and presented in article
+ * in "Computer Language" December 1990 issue.
+ *
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ * 
+ * IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+
+#include "fuzzystrmatch.h"
+
+/*
+ * Calculates Levenshtein Distance between two strings.
+ * Uses simplest and fastest cost model only, i.e. assumes a cost of 1 for
+ * each deletion, substitution, or insertion.
+ */
+PG_FUNCTION_INFO_V1(levenshtein);
+Datum
+levenshtein(PG_FUNCTION_ARGS)
+{
+	char			*str_s;
+	char			*str_s0;
+	char			*str_t;
+	int				cols = 0;
+	int				rows = 0;
+	int				*u_cells;
+	int				*l_cells;
+	int				*tmp;
+	int				i;
+	int				j;
+
+	/*
+	 * Fetch the arguments.
+	 * str_s is referred to as the "source"
+	 * cols = length of source + 1 to allow for the initialization column
+	 * str_t is referred to as the "target", rows = length of target + 1 
+	 * rows = length of target + 1 to allow for the initialization row
+	 */
+	str_s = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(0))));
+	str_t = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(1))));
+
+	cols = strlen(str_s) + 1;
+	rows = strlen(str_t) + 1;
+
+	/*
+	 * Restrict the length of the strings being compared to something reasonable
+	 * because we will have to perform rows * cols calcualtions. If longer strings need to be
+	 * compared, increase MAX_LEVENSHTEIN_STRLEN to suit (but within your tolerance for
+	 * speed and memory usage).
+	 */
+	if ((cols > MAX_LEVENSHTEIN_STRLEN + 1) || (rows > MAX_LEVENSHTEIN_STRLEN + 1))
+		elog(ERROR, "levenshtein: Arguments may not exceed %d characters in length", MAX_LEVENSHTEIN_STRLEN);
+
+	/*
+	 * If either rows or cols is 0, the answer is the other value.
+	 * This makes sense since it would take that many insertions
+	 * the build a matching string
+	 */
+
+	if (cols == 0)
+		PG_RETURN_INT32(rows);
+
+	if (rows == 0)
+		PG_RETURN_INT32(cols);
+
+	/*
+	 * Allocate two vectors of integers. One will be used for the "upper" row,
+	 * the other for the "lower" row. Initialize the "upper" row to 0..cols
+	 */
+	u_cells = palloc(sizeof(int) * cols);
+	for (i = 0; i < cols; i++)
+		u_cells[i] = i;
+
+	l_cells = palloc(sizeof(int) * cols);
+
+	/*
+	 * Use str_s0 to "rewind" the pointer to str_s in the nested for loop below
+	 */
+	str_s0 = str_s;
+
+	/*
+	 * Loop throught the rows, starting at row 1. Row 0 is used for the initial
+	 * "upper" row.
+	 */
+	for (j = 1; j < rows; j++)
+	{
+		/*
+		 * We'll always start with col 1,
+		 * and initialize lower row col 0 to j
+		 */
+		l_cells[0] = j;
+
+		for (i = 1; i < cols; i++)
+		{
+			int		c = 0;
+			int		c1 = 0;
+			int		c2 = 0;
+			int		c3 = 0;
+
+			/*
+			 * The "cost" value is 0 if the character at the current col position
+			 * in the source string, matches the character at the current row position
+			 * in the target string; cost is 1 otherwise.
+			 */
+			c = ((CHAREQ(str_s, str_t)) ? 0 : 1);
+
+			/*
+			 * c1 is upper right cell plus 1
+			 */
+			c1 = u_cells[i] + 1;
+
+			/*
+			 * c2 is lower left cell plus 1
+			 */
+			c2 = l_cells[i - 1] + 1;
+
+			/*
+			 * c3 is cell diagonally above to the left plus "cost"
+			 */
+			c3 = u_cells[i - 1] + c;
+
+			/*
+			 * The lower right cell is set to the minimum
+			 * of c1, c2, c3
+			 */
+			l_cells[i] = (c1 < c2 ? c1 : c2) < c3 ? (c1 < c2 ? c1 : c2) : c3;
+
+			/*
+			 * Increment the pointer to str_s
+			 */
+			NextChar(str_s);
+		}
+
+		/*
+		 * Lower row now becomes the upper row, and the upper row
+		 * gets reused as the new lower row.
+		 */
+		tmp = u_cells;
+		u_cells = l_cells;
+		l_cells = tmp;
+
+		/*
+		 * Increment the pointer to str_t
+		 */
+		NextChar(str_t);
+
+		/*
+		 * Rewind the pointer to str_s
+		 */
+		str_s = str_s0;
+	}
+
+	/*
+	 * Because the final value (at position row, col) was swapped from
+	 * the lower row to the upper row, that's where we'll find it.
+	 */
+	PG_RETURN_INT32(u_cells[cols - 1]);
+}
+
+/*
+ * Calculates the metaphone of an input string.
+ * Returns number of characters requested
+ * (suggested value is 4)
+ */
+PG_FUNCTION_INFO_V1(metaphone);
+Datum
+metaphone(PG_FUNCTION_ARGS)
+{
+	int			reqlen;
+	char		*str_i;
+	size_t		str_i_len;
+	char		*metaph;
+	text		*result_text;
+	int			retval;
+
+	str_i = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(0))));
+	str_i_len = strlen(str_i);
+
+	if (str_i_len > MAX_METAPHONE_STRLEN)
+		elog(ERROR, "metaphone: Input string must not exceed %d characters", MAX_METAPHONE_STRLEN);
+	if (!(str_i_len > 0))
+		elog(ERROR, "metaphone: Input string length must be > 0");
+
+	reqlen = PG_GETARG_INT32(1);
+	if (reqlen > MAX_METAPHONE_STRLEN)
+		elog(ERROR, "metaphone: Requested Metaphone output length must not exceed %d characters", MAX_METAPHONE_STRLEN);
+	if (!(reqlen > 0))
+		elog(ERROR, "metaphone: Requested Metaphone output length must be > 0");
+
+	metaph = palloc(reqlen);
+	memset(metaph, '\0', reqlen);
+
+	retval = _metaphone(str_i, reqlen, &metaph);
+	if (retval == META_SUCCESS)
+	{
+		result_text = DatumGetTextP(DirectFunctionCall1(textin, CStringGetDatum(metaph)));
+		PG_RETURN_TEXT_P(result_text);
+	}
+	else
+	{
+		elog(ERROR, "metaphone: failure");
+
+		/*
+		 * Keep the compiler quiet
+		 */
+		PG_RETURN_NULL();
+	}
+}
+
+
+/* 
+ * Original code by Michael G Schwern starts here.
+ * Code slightly modified for use as PostgreSQL
+ * function (palloc, etc). Original includes
+ * are rolled into fuzzystrmatch.h
+ *------------------------------------------------------------------*/
+
+/* I suppose I could have been using a character pointer instead of
+ * accesssing the array directly... */
+
+/* Look at the next letter in the word */
+#define Next_Letter (toupper(word[w_idx+1]))
+/* Look at the current letter in the word */
+#define Curr_Letter (toupper(word[w_idx]))
+/* Go N letters back. */
+#define Look_Back_Letter(n)	(w_idx >= n ? toupper(word[w_idx-n]) : '\0') 
+/* Previous letter.  I dunno, should this return null on failure? */
+#define Prev_Letter (Look_Back_Letter(1))
+/* Look two letters down.  It makes sure you don't walk off the string. */
+#define After_Next_Letter	(Next_Letter != '\0' ? toupper(word[w_idx+2]) \
+											     : '\0')
+#define Look_Ahead_Letter(n) (toupper(Lookahead(word+w_idx, n)))
+
+					     
+/* Allows us to safely look ahead an arbitrary # of letters */
+/* I probably could have just used strlen... */
+char Lookahead(char * word, int how_far) {
+	char letter_ahead = '\0';  /* null by default */
+	int idx;
+	for(idx = 0;  word[idx] != '\0' && idx < how_far;  idx++);
+		/* Edge forward in the string... */
+		
+	letter_ahead = word[idx];  /* idx will be either == to how_far or
+								* at the end of the string
+								*/
+	return letter_ahead;
+}
+
+
+/* phonize one letter */
+#define Phonize(c)	{(*phoned_word)[p_idx++] = c;}
+/* Slap a null character on the end of the phoned word */
+#define End_Phoned_Word	{(*phoned_word)[p_idx] = '\0';}
+/* How long is the phoned word? */
+#define Phone_Len	(p_idx)
+
+/* Note is a letter is a 'break' in the word */
+#define Isbreak(c)  (!isalpha(c))
+
+
+int _metaphone (
+	/* IN */
+	char * 	word,
+	int 	max_phonemes,
+	/* OUT */
+	char ** phoned_word 
+) {
+	int	w_idx 	= 0;	/* point in the phonization we're at. */
+	int p_idx 	= 0;	/* end of the phoned phrase */
+	
+	/*-- Parameter checks --*/
+
+	/*
+	 * Shouldn't be necessary, but left these here anyway
+	 * jec Aug 3, 2001
+	 */
+
+	/* Negative phoneme length is meaningless */
+	if (!(max_phonemes > 0))
+		elog(ERROR, "metaphone: Requested output length must be > 0");
+
+	/* Empty/null string is meaningless */
+	if ((word == NULL) || !(strlen(word) > 0))
+		elog(ERROR, "metaphone: Input string length must be > 0");
+	
+	/*-- Allocate memory for our phoned_phrase --*/
+	if (max_phonemes == 0) {	/* Assume largest possible */
+		*phoned_word = palloc(sizeof(char) * strlen(word) + 1);
+		if (!*phoned_word)
+			return META_ERROR;
+	} else {
+		*phoned_word = palloc(sizeof(char) * max_phonemes + 1);
+		if (!*phoned_word)
+			return META_ERROR;
+	}
+
+	/*-- The first phoneme has to be processed specially. --*/
+	/* Find our first letter */
+	for( ;  !isalpha(Curr_Letter);  w_idx++ ) {
+		/* On the off chance we were given nothing but crap... */
+		if( Curr_Letter == '\0' ) {
+			End_Phoned_Word
+			return META_SUCCESS; /* For testing */
+		}
+	}	
+	
+	switch (Curr_Letter) {
+		/* AE becomes E */
+		case 'A':
+			if( Next_Letter == 'E' ) {
+				Phonize('E');
+				w_idx+=2;
+			}
+			/* Remember, preserve vowels at the beginning */
+			else {
+				Phonize('A');
+				w_idx++;
+			}
+			break;
+		/* [GKP]N becomes N */
+		case 'G':
+		case 'K':
+		case 'P':
+			if( Next_Letter == 'N' ) {
+				Phonize('N');
+				w_idx+=2;
+			}
+			break;
+		/* WH becomes H, 
+		   WR becomes R 
+		   W if followed by a vowel */
+		case 'W':
+			if( Next_Letter == 'H' ||
+			    Next_Letter == 'R' ) 
+			{
+			  Phonize(Next_Letter);
+			  w_idx+=2;
+			}
+			else if ( isvowel(Next_Letter) ) {
+			  Phonize('W');
+			  w_idx+=2;
+			}
+			/* else ignore */
+			break;
+		/* X becomes S */
+		case 'X':
+			Phonize('S');
+			w_idx++;
+			break;
+		/* Vowels are kept */
+		/* We did A already
+		case 'A':
+		case 'a':
+		*/
+		case 'E':
+		case 'I':
+		case 'O':
+		case 'U':
+			Phonize(Curr_Letter);
+			w_idx++;
+			break;
+		default:
+			/* do nothing */
+			break;
+	}
+	
+	
+	
+	/* On to the metaphoning */
+	for(;  Curr_Letter != '\0' && 
+	        (max_phonemes == 0 || Phone_Len < max_phonemes);  
+	    w_idx++) {
+		/* How many letters to skip because an eariler encoding handled 	
+		 * multiple letters */
+		unsigned short int skip_letter = 0;	
+								
+
+		/* THOUGHT:  It would be nice if, rather than having things like...
+		 * well, SCI.  For SCI you encode the S, then have to remember
+		 * to skip the C.  So the phonome SCI invades both S and C.  It would
+		 * be better, IMHO, to skip the C from the S part of the encoding.
+		 * Hell, I'm trying it.
+		 */
+	
+		/* Ignore non-alphas */
+		if( !isalpha(Curr_Letter) )
+			continue;
+			
+		/* Drop duplicates, except CC */
+		if( Curr_Letter == Prev_Letter &&
+			Curr_Letter != 'C' )
+			continue;
+		
+		switch (Curr_Letter) {
+			/* B -> B unless in MB */
+			case 'B':
+				if( Prev_Letter != 'M' )
+					Phonize('B');
+				break;
+			/* 'sh' if -CIA- or -CH, but not SCH, except SCHW.
+			 * (SCHW is handled in S)
+			 *  S if -CI-, -CE- or -CY-
+			 *  dropped if -SCI-, SCE-, -SCY- (handed in S)
+			 *  else K
+			 */
+			case 'C':
+				if( MAKESOFT(Next_Letter) ) {	/* C[IEY] */
+					if( After_Next_Letter == 'A' &&
+						Next_Letter == 'I' ) { /* CIA */
+						Phonize(SH);
+					}
+					/* SC[IEY] */
+					else if ( Prev_Letter == 'S' ) {
+					  /* Dropped */
+					}
+					else {
+					  Phonize('S');
+					}
+				}
+				else if ( Next_Letter == 'H' ) {
+#ifndef USE_TRADITIONAL_METAPHONE
+					if( After_Next_Letter == 'R' ||
+						Prev_Letter == 'S' ) { /* Christ, School */
+						Phonize('K');
+					}
+					else {
+						Phonize(SH);
+					}
+#else
+					Phonize(SH);
+#endif
+					skip_letter++;
+				}
+				else {
+					Phonize('K');
+				}
+				break;
+			/* J if in -DGE-, -DGI- or -DGY-
+			 * else T
+			 */
+			case 'D':
+				if( Next_Letter == 'G' &&
+					MAKESOFT(After_Next_Letter) ) {
+					Phonize('J');
+					skip_letter++;
+				}
+				else
+					Phonize('T');
+				break;
+			/* F if in -GH and not B--GH, D--GH, -H--GH, -H---GH
+			 * else dropped if -GNED, -GN, 
+			 * else dropped if -DGE-, -DGI- or -DGY- (handled in D)
+			 * else J if in -GE-, -GI, -GY and not GG
+			 * else K
+			 */
+			case 'G':
+				if( Next_Letter == 'H' ) {
+					if( !( NOGHTOF(Look_Back_Letter(3)) ||
+						   Look_Back_Letter(4) == 'H' ) ) {
+						Phonize('F');
+						skip_letter++;
+					}
+					else {
+						/* silent */
+					}
+				}
+				else if( Next_Letter == 'N' ) {
+					if( Isbreak(After_Next_Letter) ||
+						( After_Next_Letter == 'E' &&
+						  Look_Ahead_Letter(3) == 'D' ) ) {
+						/* dropped */
+					}
+					else
+						Phonize('K');
+				}
+				else if( MAKESOFT(Next_Letter) &&
+						 Prev_Letter != 'G' ) {
+					Phonize('J');
+				}
+				else {
+					Phonize('K');
+				}
+				break;
+			/* H if before a vowel and not after C,G,P,S,T */
+			case 'H':
+				if( isvowel(Next_Letter) &&
+					!AFFECTH(Prev_Letter) )
+					Phonize('H');
+				break;
+			/* dropped if after C
+			 * else K
+			 */
+			case 'K':
+				if( Prev_Letter != 'C' )
+					Phonize('K');
+				break;
+			/* F if before H
+			 * else P
+			 */
+			case 'P':
+				if( Next_Letter == 'H' ) {
+					Phonize('F');
+				}
+				else {
+					Phonize('P');
+				}
+				break;
+			/* K
+			 */
+			case 'Q':
+				Phonize('K');
+				break;
+			/* 'sh' in -SH-, -SIO- or -SIA- or -SCHW-
+			 * else S
+			 */
+			case 'S':
+				if( Next_Letter == 'I' &&
+					( After_Next_Letter == 'O' ||
+					  After_Next_Letter == 'A' ) ) {
+					Phonize(SH);
+				}
+				else if ( Next_Letter == 'H' ) {
+					Phonize(SH);
+					skip_letter++;
+				}
+#ifndef USE_TRADITIONAL_METAPHONE
+				else if ( Next_Letter == 'C' &&
+					  Look_Ahead_Letter(2) == 'H' &&
+					  Look_Ahead_Letter(3) == 'W' ) {
+					Phonize(SH);
+					skip_letter += 2;
+				}
+#endif
+				else {
+					Phonize('S');
+				}
+				break;
+			/* 'sh' in -TIA- or -TIO-
+			 * else 'th' before H
+			 * else T
+			 */
+			case 'T':
+				if( Next_Letter == 'I' &&
+					( After_Next_Letter == 'O' ||
+					  After_Next_Letter == 'A' ) ) {
+					Phonize(SH);
+				}
+				else if ( Next_Letter == 'H' ) {
+					Phonize(TH);
+					skip_letter++;
+				}
+				else {
+					Phonize('T');
+				}
+				break;
+			/* F */
+			case 'V':
+				Phonize('F');
+				break;
+			/* W before a vowel, else dropped */
+			case 'W':
+				if( isvowel(Next_Letter) )
+					Phonize('W');
+				break;
+			/* KS */
+			case 'X':
+				Phonize('K');
+				Phonize('S');
+				break;
+			/* Y if followed by a vowel */
+			case 'Y':
+				if( isvowel(Next_Letter) )
+					Phonize('Y');
+				break;
+			/* S */
+			case 'Z':
+				Phonize('S');
+				break;
+			/* No transformation */
+			case 'F':
+			case 'J':
+			case 'L':
+			case 'M':
+			case 'N':
+			case 'R':
+				Phonize(Curr_Letter);
+				break;
+			default:
+				/* nothing */
+				break;
+		} /* END SWITCH */
+		
+		w_idx += skip_letter;
+	} /* END FOR */
+	
+	End_Phoned_Word;
+	
+	return(META_SUCCESS);
+} /* END metaphone */

contrib/fuzzystrmatch/fuzzystrmatch.h

+/*
+ * fuzzystrmatch.h
+ *
+ * Functions for "fuzzy" comparison of strings
+ *
+ * Copyright (c) Joseph Conway <joseph.conway@home.com>, 2001;
+ *
+ * levenshtein()
+ * -------------
+ * Written based on a description of the algorithm by Michael Gilleland
+ * found at http://www.merriampark.com/ld.htm
+ * Also looked at levenshtein.c in the PHP 4.0.6 distribution for
+ * inspiration.
+ *
+ * metaphone()
+ * -----------
+ * Modified for PostgreSQL by Joe Conway.
+ * Based on CPAN's "Text-Metaphone-1.96" by Michael G Schwern <schwern@pobox.com>
+ * Code slightly modified for use as PostgreSQL function (palloc, elog, etc).
+ * Metaphone was originally created by Lawrence Philips and presented in article
+ * in "Computer Language" December 1990 issue.
+ *
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ * 
+ * IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+
+#ifndef FUZZYSTRMATCH_H
+#define FUZZYSTRMATCH_H
+
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#include "postgres.h"
+#include "fmgr.h"
+#include "utils/builtins.h"
+
+
+#define MAX_LEVENSHTEIN_STRLEN		255
+#define MAX_METAPHONE_STRLEN		255
+
+typedef struct dynmatrix
+{
+	int		   value;
+} dynmat;
+
+
+/*
+ * External declarations
+ */
+extern Datum levenshtein(PG_FUNCTION_ARGS);
+extern Datum metaphone(PG_FUNCTION_ARGS);
+
+/*
+ * Internal declarations
+ */
+
+
+
+#define STRLEN(p) strlen(p)
+#define CHAREQ(p1, p2) (*(p1) == *(p2))
+#define NextChar(p) ((p)++)
+
+
+/* 
+ * Original code by Michael G Schwern starts here.
+ * Code slightly modified for use as PostgreSQL
+ * function (combined *.h into here).
+ *------------------------------------------------------------------*/
+
+/**************************************************************************
+	metaphone -- Breaks english phrases down into their phonemes.
+	
+	Input
+		word			-- 	An english word to be phonized
+		max_phonemes 	-- 	How many phonemes to calculate.  If 0, then it
+							will phonize the entire phrase.
+		phoned_word  	-- 	The final phonized word.  (We'll allocate the
+							memory.)
+	Output
+		error	--	A simple error flag, returns TRUE or FALSE
+		
+	NOTES:  ALL non-alpha characters are ignored, this includes whitespace,
+	although non-alpha characters will break up phonemes.
+****************************************************************************/
+
+
+/**************************************************************************
+	my constants -- constants I like
+	
+	Probably redundant.
+	
+***************************************************************************/
+
+#define META_ERROR			FALSE
+#define META_SUCCESS		TRUE
+#define META_FAILURE		FALSE
+
+
+/*  I add modifications to the traditional metaphone algorithm that you
+	might find in books.  Define this if you want metaphone to behave
+	traditionally */
+#undef USE_TRADITIONAL_METAPHONE
+
+/* Special encodings */
+#define  SH 	'X'
+#define  TH		'0'
+
+char Lookahead(char * word, int how_far);
+int _metaphone (
+	/* IN */
+	char * 	word,
+	int 	max_phonemes,
+	/* OUT */
+	char **	phoned_word
+);
+
+/* Metachar.h ... little bits about characters for metaphone */
+
+
+/*-- Character encoding array & accessing macros --*/
+/* Stolen directly out of the book... */
+char _codes[26] = {
+	1,16,4,16,9,2,4,16,9,2,0,2,2,2,1,4,0,2,4,4,1,0,0,0,8,0
+/*  a  b c  d e f g  h i j k l m n o p q r s t u v w x y z */
+};
+
+
+#define ENCODE(c) (isalpha(c) ? _codes[((toupper(c)) - 'A')] : 0)
+
+#define isvowel(c)	(ENCODE(c) & 1)		/* AEIOU */
+
+/* These letters are passed through unchanged */
+#define NOCHANGE(c)	(ENCODE(c) & 2) 	/* FJMNR */
+
+/* These form dipthongs when preceding H */
+#define AFFECTH(c)	(ENCODE(c) & 4) 	/* CGPST */
+
+/* These make C and G soft */
+#define MAKESOFT(c)	(ENCODE(c) & 8) 	/* EIY */
+
+/* These prevent GH from becoming F */
+#define NOGHTOF(c)	(ENCODE(c) & 16) 	/* BDH */
+
+
+#endif	 /* FUZZYSTRMATCH_H */

contrib/fuzzystrmatch/fuzzystrmatch.sql.in

+CREATE FUNCTION levenshtein (text,text) RETURNS int
+  AS 'MODULE_PATHNAME','levenshtein' LANGUAGE 'c' with (iscachable, isstrict);
+
+CREATE FUNCTION metaphone (text,int) RETURNS text
+  AS 'MODULE_PATHNAME','metaphone' LANGUAGE 'c' with (iscachable, isstrict);