fuzzystrmatch.c

Go to the documentation of this file.

/*
 * fuzzystrmatch.c
 *
 * Functions for "fuzzy" comparison of strings
 *
 * Joe Conway <mail@joeconway.com>
 *
 * contrib/fuzzystrmatch/fuzzystrmatch.c
 * Copyright (c) 2001-2026, PostgreSQL Global Development Group
 * ALL RIGHTS RESERVED;
 *
 * 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 "postgres.h"
 
#include <ctype.h>
 
#include "utils/builtins.h"
#include "utils/varlena.h"
#include "varatt.h"
 
PG_MODULE_MAGIC_EXT(
                    .name = "fuzzystrmatch",
                    .version = PG_VERSION
);
 
/*
 * Soundex
 */
static void _soundex(const char *instr, char *outstr);
 
#define SOUNDEX_LEN 4
 
/*                                  ABCDEFGHIJKLMNOPQRSTUVWXYZ */
static const char *const soundex_table = "01230120022455012623010202";
 
static char
soundex_code(char letter)
{
    letter = pg_ascii_toupper((unsigned char) letter);
    /* Defend against non-ASCII letters */
    if (letter >= 'A' && letter <= 'Z')
        return soundex_table[letter - 'A'];
    return letter;
}
 
/*
 * Metaphone
 */
#define MAX_METAPHONE_STRLEN        255
 
/*
 * Original code by Michael G Schwern starts here.
 * Code slightly modified for use as PostgreSQL function.
 */
 
 
/**************************************************************************
    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.
****************************************************************************/
 
 
/*
 * 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'
 
static char Lookahead(char *word, int how_far);
static void _metaphone(char *word, int max_phonemes, char **phoned_word);
 
/* Metachar.h ... little bits about characters for metaphone */
 
 
/*-- Character encoding array & accessing macros --*/
/* Stolen directly out of the book... */
static const 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 */
};
 
static int
getcode(char c)
{
    c = pg_ascii_toupper((unsigned char) c);
    /* Defend against non-ASCII letters */
    if (c >= 'A' && c <= 'Z')
        return _codes[c - 'A'];
 
    return 0;
}
 
static bool
ascii_isalpha(char c)
{
    return (c >= 'A' && c <= 'Z') ||
        (c >= 'a' && c <= 'z');
}
 
#define isvowel(c)  (getcode(c) & 1)    /* AEIOU */
 
/* These letters are passed through unchanged */
#define NOCHANGE(c) (getcode(c) & 2)    /* FJMNR */
 
/* These form diphthongs when preceding H */
#define AFFECTH(c)  (getcode(c) & 4)    /* CGPST */
 
/* These make C and G soft */
#define MAKESOFT(c) (getcode(c) & 8)    /* EIY */
 
/* These prevent GH from becoming F */
#define NOGHTOF(c)  (getcode(c) & 16)   /* BDH */
 
PG_FUNCTION_INFO_V1(levenshtein_with_costs);
Datum
levenshtein_with_costs(PG_FUNCTION_ARGS)
{
    text       *src = PG_GETARG_TEXT_PP(0);
    text       *dst = PG_GETARG_TEXT_PP(1);
    int         ins_c = PG_GETARG_INT32(2);
    int         del_c = PG_GETARG_INT32(3);
    int         sub_c = PG_GETARG_INT32(4);
    const char *s_data;
    const char *t_data;
    int         s_bytes,
                t_bytes;
 
    /* Extract a pointer to the actual character data */
    s_data = VARDATA_ANY(src);
    t_data = VARDATA_ANY(dst);
    /* Determine length of each string in bytes */
    s_bytes = VARSIZE_ANY_EXHDR(src);
    t_bytes = VARSIZE_ANY_EXHDR(dst);
 
    PG_RETURN_INT32(varstr_levenshtein(s_data, s_bytes, t_data, t_bytes,
                                       ins_c, del_c, sub_c, false));
}
 
 
PG_FUNCTION_INFO_V1(levenshtein);
Datum
levenshtein(PG_FUNCTION_ARGS)
{
    text       *src = PG_GETARG_TEXT_PP(0);
    text       *dst = PG_GETARG_TEXT_PP(1);
    const char *s_data;
    const char *t_data;
    int         s_bytes,
                t_bytes;
 
    /* Extract a pointer to the actual character data */
    s_data = VARDATA_ANY(src);
    t_data = VARDATA_ANY(dst);
    /* Determine length of each string in bytes */
    s_bytes = VARSIZE_ANY_EXHDR(src);
    t_bytes = VARSIZE_ANY_EXHDR(dst);
 
    PG_RETURN_INT32(varstr_levenshtein(s_data, s_bytes, t_data, t_bytes,
                                       1, 1, 1, false));
}
 
 
PG_FUNCTION_INFO_V1(levenshtein_less_equal_with_costs);
Datum
levenshtein_less_equal_with_costs(PG_FUNCTION_ARGS)
{
    text       *src = PG_GETARG_TEXT_PP(0);
    text       *dst = PG_GETARG_TEXT_PP(1);
    int         ins_c = PG_GETARG_INT32(2);
    int         del_c = PG_GETARG_INT32(3);
    int         sub_c = PG_GETARG_INT32(4);
    int         max_d = PG_GETARG_INT32(5);
    const char *s_data;
    const char *t_data;
    int         s_bytes,
                t_bytes;
 
    /* Extract a pointer to the actual character data */
    s_data = VARDATA_ANY(src);
    t_data = VARDATA_ANY(dst);
    /* Determine length of each string in bytes */
    s_bytes = VARSIZE_ANY_EXHDR(src);
    t_bytes = VARSIZE_ANY_EXHDR(dst);
 
    PG_RETURN_INT32(varstr_levenshtein_less_equal(s_data, s_bytes,
                                                  t_data, t_bytes,
                                                  ins_c, del_c, sub_c,
                                                  max_d, false));
}
 
 
PG_FUNCTION_INFO_V1(levenshtein_less_equal);
Datum
levenshtein_less_equal(PG_FUNCTION_ARGS)
{
    text       *src = PG_GETARG_TEXT_PP(0);
    text       *dst = PG_GETARG_TEXT_PP(1);
    int         max_d = PG_GETARG_INT32(2);
    const char *s_data;
    const char *t_data;
    int         s_bytes,
                t_bytes;
 
    /* Extract a pointer to the actual character data */
    s_data = VARDATA_ANY(src);
    t_data = VARDATA_ANY(dst);
    /* Determine length of each string in bytes */
    s_bytes = VARSIZE_ANY_EXHDR(src);
    t_bytes = VARSIZE_ANY_EXHDR(dst);
 
    PG_RETURN_INT32(varstr_levenshtein_less_equal(s_data, s_bytes,
                                                  t_data, t_bytes,
                                                  1, 1, 1,
                                                  max_d, false));
}
 
 
/*
 * 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)
{
    char       *str_i = TextDatumGetCString(PG_GETARG_DATUM(0));
    size_t      str_i_len = strlen(str_i);
    int         reqlen;
    char       *metaph;
 
    /* return an empty string if we receive one */
    if (!(str_i_len > 0))
        PG_RETURN_TEXT_P(cstring_to_text(""));
 
    if (str_i_len > MAX_METAPHONE_STRLEN)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("argument exceeds the maximum length of %d bytes",
                        MAX_METAPHONE_STRLEN)));
 
    reqlen = PG_GETARG_INT32(1);
    if (reqlen > MAX_METAPHONE_STRLEN)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("output exceeds the maximum length of %d bytes",
                        MAX_METAPHONE_STRLEN)));
 
    if (!(reqlen > 0))
        ereport(ERROR,
                (errcode(ERRCODE_ZERO_LENGTH_CHARACTER_STRING),
                 errmsg("output cannot be empty string")));
 
    _metaphone(str_i, reqlen, &metaph);
    PG_RETURN_TEXT_P(cstring_to_text(metaph));
}
 
 
/*
 * Original code by Michael G Schwern starts here.
 * Code slightly modified for use as PostgreSQL
 * function (palloc, etc).
 */
 
/*
 * I suppose I could have been using a character pointer instead of
 * accessing the array directly...
 */
 
/* Look at the next letter in the word */
#define Next_Letter (pg_ascii_toupper((unsigned char) word[w_idx+1]))
/* Look at the current letter in the word */
#define Curr_Letter (pg_ascii_toupper((unsigned char) word[w_idx]))
/* Go N letters back. */
#define Look_Back_Letter(n) \
    (w_idx >= (n) ? pg_ascii_toupper((unsigned char) 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' ? pg_ascii_toupper((unsigned char) word[w_idx+2]) : '\0')
#define Look_Ahead_Letter(n) pg_ascii_toupper((unsigned char) Lookahead(word+w_idx, n))
 
 
/* Allows us to safely look ahead an arbitrary # of letters */
/* I probably could have just used strlen... */
static 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)  do {(*phoned_word)[p_idx++] = c;} while (0)
/* Slap a null character on the end of the phoned word */
#define End_Phoned_Word do {(*phoned_word)[p_idx] = '\0';} while (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)  (!ascii_isalpha((unsigned char) (c)))
 
 
static void
_metaphone(char *word,          /* IN */
           int max_phonemes,
           char **phoned_word)  /* OUT */
{
    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))
        /* internal error */
        elog(ERROR, "metaphone: Requested output length must be > 0");
 
    /* Empty/null string is meaningless */
    if ((word == NULL) || !(strlen(word) > 0))
        /* internal error */
        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);
    }
    else
    {
        *phoned_word = palloc(sizeof(char) * max_phonemes + 1);
    }
 
    /*-- The first phoneme has to be processed specially. --*/
    /* Find our first letter */
    for (; !ascii_isalpha((unsigned char) (Curr_Letter)); w_idx++)
    {
        /* On the off chance we were given nothing but crap... */
        if (Curr_Letter == '\0')
        {
            End_Phoned_Word;
            return;
        }
    }
 
    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 earlier 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 (!ascii_isalpha((unsigned char) (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');
                if (max_phonemes == 0 || Phone_Len < max_phonemes)
                    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;
}                               /* END metaphone */
 
 
/*
 * SQL function: soundex(text) returns text
 */
PG_FUNCTION_INFO_V1(soundex);
 
Datum
soundex(PG_FUNCTION_ARGS)
{
    char        outstr[SOUNDEX_LEN + 1];
    char       *arg;
 
    arg = text_to_cstring(PG_GETARG_TEXT_PP(0));
 
    _soundex(arg, outstr);
 
    PG_RETURN_TEXT_P(cstring_to_text(outstr));
}
 
static void
_soundex(const char *instr, char *outstr)
{
    int         count;
 
    Assert(instr);
    Assert(outstr);
 
    /* Skip leading non-alphabetic characters */
    while (*instr && !ascii_isalpha((unsigned char) *instr))
        ++instr;
 
    /* If no string left, return all-zeroes buffer */
    if (!*instr)
    {
        memset(outstr, '\0', SOUNDEX_LEN + 1);
        return;
    }
 
    /* Take the first letter as is */
    *outstr++ = (char) pg_ascii_toupper((unsigned char) *instr++);
 
    count = 1;
    while (*instr && count < SOUNDEX_LEN)
    {
        if (ascii_isalpha((unsigned char) *instr) &&
            soundex_code(*instr) != soundex_code(*(instr - 1)))
        {
            *outstr = soundex_code(*instr);
            if (*outstr != '0')
            {
                ++outstr;
                ++count;
            }
        }
        ++instr;
    }
 
    /* Fill with 0's */
    while (count < SOUNDEX_LEN)
    {
        *outstr = '0';
        ++outstr;
        ++count;
    }
 
    /* And null-terminate */
    *outstr = '\0';
}
 
PG_FUNCTION_INFO_V1(difference);
 
Datum
difference(PG_FUNCTION_ARGS)
{
    char        sndx1[SOUNDEX_LEN + 1],
                sndx2[SOUNDEX_LEN + 1];
    int         i,
                result;
 
    _soundex(text_to_cstring(PG_GETARG_TEXT_PP(0)), sndx1);
    _soundex(text_to_cstring(PG_GETARG_TEXT_PP(1)), sndx2);
 
    result = 0;
    for (i = 0; i < SOUNDEX_LEN; i++)
    {
        if (sndx1[i] == sndx2[i])
            result++;
    }
 
    PG_RETURN_INT32(result);
}