trgm_op.c

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/*
 * contrib/pg_trgm/trgm_op.c
 */
#include "postgres.h"
 
#include <ctype.h>
 
#include "catalog/pg_collation_d.h"
#include "catalog/pg_type.h"
#include "common/int.h"
#include "lib/qunique.h"
#include "miscadmin.h"
#include "trgm.h"
#include "tsearch/ts_locale.h"
#include "utils/formatting.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/pg_crc.h"
 
PG_MODULE_MAGIC_EXT(
                    .name = "pg_trgm",
                    .version = PG_VERSION
);
 
/* GUC variables */
double      similarity_threshold = 0.3f;
double      word_similarity_threshold = 0.6f;
double      strict_word_similarity_threshold = 0.5f;
 
PG_FUNCTION_INFO_V1(set_limit);
PG_FUNCTION_INFO_V1(show_limit);
PG_FUNCTION_INFO_V1(show_trgm);
PG_FUNCTION_INFO_V1(similarity);
PG_FUNCTION_INFO_V1(word_similarity);
PG_FUNCTION_INFO_V1(strict_word_similarity);
PG_FUNCTION_INFO_V1(similarity_dist);
PG_FUNCTION_INFO_V1(similarity_op);
PG_FUNCTION_INFO_V1(word_similarity_op);
PG_FUNCTION_INFO_V1(word_similarity_commutator_op);
PG_FUNCTION_INFO_V1(word_similarity_dist_op);
PG_FUNCTION_INFO_V1(word_similarity_dist_commutator_op);
PG_FUNCTION_INFO_V1(strict_word_similarity_op);
PG_FUNCTION_INFO_V1(strict_word_similarity_commutator_op);
PG_FUNCTION_INFO_V1(strict_word_similarity_dist_op);
PG_FUNCTION_INFO_V1(strict_word_similarity_dist_commutator_op);
 
static int  CMPTRGM_CHOOSE(const void *a, const void *b);
int         (*CMPTRGM) (const void *a, const void *b) = CMPTRGM_CHOOSE;
 
/* Trigram with position */
typedef struct
{
    trgm        trg;
    int         index;
} pos_trgm;
 
/* Trigram bound type */
typedef uint8 TrgmBound;
#define TRGM_BOUND_LEFT             0x01    /* trigram is left bound of word */
#define TRGM_BOUND_RIGHT            0x02    /* trigram is right bound of word */
 
/* Word similarity flags */
#define WORD_SIMILARITY_CHECK_ONLY  0x01    /* only check existence of similar
                                             * search pattern in text */
#define WORD_SIMILARITY_STRICT      0x02    /* force bounds of extent to match
                                             * word bounds */
 
/*
 * A growable array of trigrams
 *
 * The actual array of trigrams is in 'datum'.  Note that the other fields in
 * 'datum', i.e. datum->flags and the varlena length, are not kept up to date
 * when items are added to the growable array.  We merely reserve the space
 * for them here.  You must fill those other fields before using 'datum' as a
 * proper TRGM datum.
 */
typedef struct
{
    TRGM       *datum;          /* trigram array */
    int         length;         /* number of trigrams in the array */
    int         allocated;      /* allocated size of 'datum' (# of trigrams) */
} growable_trgm_array;
 
/*
 * Allocate a new growable array.
 *
 * 'slen' is the size of the source string that we're extracting the trigrams
 * from.  It is used to choose the initial size of the array.
 */
static void
init_trgm_array(growable_trgm_array *arr, int slen)
{
    size_t      init_size;
 
    /*
     * In the extreme case, the input string consists entirely of one
     * character words, like "a b c", where each word is expanded to two
     * trigrams.  This is not a strict upper bound though, because when
     * IGNORECASE is defined, we convert the input string to lowercase before
     * extracting the trigrams, which in rare cases can expand one input
     * character into multiple characters.
     */
    init_size = (size_t) slen + 1;
 
    /*
     * Guard against possible overflow in the palloc request.  (We don't worry
     * about the additive constants, since palloc can detect requests that are
     * a little above MaxAllocSize --- we just need to prevent integer
     * overflow in the multiplications.)
     */
    if (init_size > MaxAllocSize / sizeof(trgm))
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("out of memory")));
 
    arr->datum = palloc(CALCGTSIZE(ARRKEY, init_size));
    arr->allocated = init_size;
    arr->length = 0;
}
 
/* Make sure the array can hold at least 'needed' more trigrams */
static void
enlarge_trgm_array(growable_trgm_array *arr, int needed)
{
    size_t      new_needed = (size_t) arr->length + needed;
 
    if (new_needed > arr->allocated)
    {
        /* Guard against possible overflow, like in init_trgm_array */
        if (new_needed > MaxAllocSize / sizeof(trgm))
            ereport(ERROR,
                    (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                     errmsg("out of memory")));
 
        arr->datum = repalloc(arr->datum, CALCGTSIZE(ARRKEY, new_needed));
        arr->allocated = new_needed;
    }
}
 
/*
 * Module load callback
 */
void
_PG_init(void)
{
    /* Define custom GUC variables. */
    DefineCustomRealVariable("pg_trgm.similarity_threshold",
                             "Sets the threshold used by the % operator.",
                             "Valid range is 0.0 .. 1.0.",
                             &similarity_threshold,
                             0.3f,
                             0.0,
                             1.0,
                             PGC_USERSET,
                             0,
                             NULL,
                             NULL,
                             NULL);
    DefineCustomRealVariable("pg_trgm.word_similarity_threshold",
                             "Sets the threshold used by the <% operator.",
                             "Valid range is 0.0 .. 1.0.",
                             &word_similarity_threshold,
                             0.6f,
                             0.0,
                             1.0,
                             PGC_USERSET,
                             0,
                             NULL,
                             NULL,
                             NULL);
    DefineCustomRealVariable("pg_trgm.strict_word_similarity_threshold",
                             "Sets the threshold used by the <<% operator.",
                             "Valid range is 0.0 .. 1.0.",
                             &strict_word_similarity_threshold,
                             0.5f,
                             0.0,
                             1.0,
                             PGC_USERSET,
                             0,
                             NULL,
                             NULL,
                             NULL);
 
    MarkGUCPrefixReserved("pg_trgm");
}
 
#define CMPCHAR(a,b) ( ((a)==(b)) ? 0 : ( ((a)<(b)) ? -1 : 1 ) )
 
/*
 * Functions for comparing two trgms while treating each char as "signed char" or
 * "unsigned char".
 */
static inline int
CMPTRGM_SIGNED(const void *a, const void *b)
{
#define CMPPCHAR_S(a,b,i)  CMPCHAR( *(((const signed char*)(a))+i), *(((const signed char*)(b))+i) )
 
    return CMPPCHAR_S(a, b, 0) ? CMPPCHAR_S(a, b, 0)
        : (CMPPCHAR_S(a, b, 1) ? CMPPCHAR_S(a, b, 1)
           : CMPPCHAR_S(a, b, 2));
}
 
static inline int
CMPTRGM_UNSIGNED(const void *a, const void *b)
{
#define CMPPCHAR_UNS(a,b,i)  CMPCHAR( *(((const unsigned char*)(a))+i), *(((const unsigned char*)(b))+i) )
 
    return CMPPCHAR_UNS(a, b, 0) ? CMPPCHAR_UNS(a, b, 0)
        : (CMPPCHAR_UNS(a, b, 1) ? CMPPCHAR_UNS(a, b, 1)
           : CMPPCHAR_UNS(a, b, 2));
}
 
/*
 * This gets called on the first call. It replaces the function pointer so
 * that subsequent calls are routed directly to the chosen implementation.
 */
static int
CMPTRGM_CHOOSE(const void *a, const void *b)
{
    if (GetDefaultCharSignedness())
        CMPTRGM = CMPTRGM_SIGNED;
    else
        CMPTRGM = CMPTRGM_UNSIGNED;
 
    return CMPTRGM(a, b);
}
 
#define ST_SORT trigram_qsort_signed
#define ST_ELEMENT_TYPE_VOID
#define ST_COMPARE(a, b) CMPTRGM_SIGNED(a, b)
#define ST_SCOPE static
#define ST_DEFINE
#define ST_DECLARE
#include "lib/sort_template.h"
 
#define ST_SORT trigram_qsort_unsigned
#define ST_ELEMENT_TYPE_VOID
#define ST_COMPARE(a, b) CMPTRGM_UNSIGNED(a, b)
#define ST_SCOPE static
#define ST_DEFINE
#define ST_DECLARE
#include "lib/sort_template.h"
 
/* Sort an array of trigrams, handling signedness correctly */
static void
trigram_qsort(trgm *array, size_t n)
{
    if (GetDefaultCharSignedness())
        trigram_qsort_signed(array, n, sizeof(trgm));
    else
        trigram_qsort_unsigned(array, n, sizeof(trgm));
}
 
 
/*
 * Compare two trigrams for equality.  This has the same signature as
 * comparison functions used for sorting, so that this can be used with
 * qunique().  This doesn't need separate versions for "signed char" and "
 * unsigned char" because equality is the same for both.
 */
static inline int
CMPTRGM_EQ(const void *a, const void *b)
{
    char       *aa = (char *) a;
    char       *bb = (char *) b;
 
    return aa[0] != bb[0] || aa[1] != bb[1] || aa[2] != bb[2] ? 1 : 0;
}
 
/* Deduplicate an array of trigrams */
static size_t
trigram_qunique(trgm *array, size_t n)
{
    return qunique(array, n, sizeof(trgm), CMPTRGM_EQ);
}
 
/*
 * Deprecated function.
 * Use "pg_trgm.similarity_threshold" GUC variable instead of this function.
 */
Datum
set_limit(PG_FUNCTION_ARGS)
{
    float4      nlimit = PG_GETARG_FLOAT4(0);
    char       *nlimit_str;
    Oid         func_out_oid;
    bool        is_varlena;
 
    getTypeOutputInfo(FLOAT4OID, &func_out_oid, &is_varlena);
 
    nlimit_str = OidOutputFunctionCall(func_out_oid, Float4GetDatum(nlimit));
 
    SetConfigOption("pg_trgm.similarity_threshold", nlimit_str,
                    PGC_USERSET, PGC_S_SESSION);
 
    PG_RETURN_FLOAT4(similarity_threshold);
}
 
 
/*
 * Get similarity threshold for given index scan strategy number.
 */
double
index_strategy_get_limit(StrategyNumber strategy)
{
    switch (strategy)
    {
        case SimilarityStrategyNumber:
            return similarity_threshold;
        case WordSimilarityStrategyNumber:
            return word_similarity_threshold;
        case StrictWordSimilarityStrategyNumber:
            return strict_word_similarity_threshold;
        default:
            elog(ERROR, "unrecognized strategy number: %d", strategy);
            break;
    }
 
    return 0.0;                 /* keep compiler quiet */
}
 
/*
 * Deprecated function.
 * Use "pg_trgm.similarity_threshold" GUC variable instead of this function.
 */
Datum
show_limit(PG_FUNCTION_ARGS)
{
    PG_RETURN_FLOAT4(similarity_threshold);
}
 
/*
 * Finds first word in string, returns pointer to the word,
 * endword points to the character after word
 */
static char *
find_word(char *str, int lenstr, char **endword)
{
    char       *beginword = str;
    const char *endstr = str + lenstr;
 
    while (beginword < endstr)
    {
        int         clen = pg_mblen_range(beginword, endstr);
 
        if (ISWORDCHR(beginword, clen))
            break;
        beginword += clen;
    }
 
    if (beginword >= endstr)
        return NULL;
 
    *endword = beginword;
    while (*endword < endstr)
    {
        int         clen = pg_mblen_range(*endword, endstr);
 
        if (!ISWORDCHR(*endword, clen))
            break;
        *endword += clen;
    }
 
    return beginword;
}
 
/*
 * Reduce a trigram (three possibly multi-byte characters) to a trgm,
 * which is always exactly three bytes.  If we have three single-byte
 * characters, we just use them as-is; otherwise we form a hash value.
 */
void
compact_trigram(trgm *tptr, char *str, int bytelen)
{
    if (bytelen == 3)
    {
        CPTRGM(tptr, str);
    }
    else
    {
        pg_crc32    crc;
 
        INIT_LEGACY_CRC32(crc);
        COMP_LEGACY_CRC32(crc, str, bytelen);
        FIN_LEGACY_CRC32(crc);
 
        /*
         * use only 3 upper bytes from crc, hope, it's good enough hashing
         */
        CPTRGM(tptr, &crc);
    }
}
 
/*
 * Adds trigrams from the word in 'str' (already padded if necessary).
 */
static void
make_trigrams(growable_trgm_array *dst, char *str, int bytelen)
{
    trgm       *tptr;
    char       *ptr = str;
 
    if (bytelen < 3)
        return;
 
    /* max number of trigrams = strlen - 2 */
    enlarge_trgm_array(dst, bytelen - 2);
    tptr = GETARR(dst->datum) + dst->length;
 
    if (pg_encoding_max_length(GetDatabaseEncoding()) == 1)
    {
        while (ptr < str + bytelen - 2)
        {
            CPTRGM(tptr, ptr);
            ptr++;
            tptr++;
        }
    }
    else
    {
        int         lenfirst,
                    lenmiddle,
                    lenlast;
        char       *endptr;
 
        /*
         * Fast path as long as there are no multibyte characters
         */
        if (!IS_HIGHBIT_SET(ptr[0]) && !IS_HIGHBIT_SET(ptr[1]))
        {
            while (!IS_HIGHBIT_SET(ptr[2]))
            {
                CPTRGM(tptr, ptr);
                ptr++;
                tptr++;
 
                if (ptr == str + bytelen - 2)
                    goto done;
            }
 
            lenfirst = 1;
            lenmiddle = 1;
            lenlast = pg_mblen_unbounded(ptr + 2);
        }
        else
        {
            lenfirst = pg_mblen_unbounded(ptr);
            if (ptr + lenfirst >= str + bytelen)
                goto done;
            lenmiddle = pg_mblen_unbounded(ptr + lenfirst);
            if (ptr + lenfirst + lenmiddle >= str + bytelen)
                goto done;
            lenlast = pg_mblen_unbounded(ptr + lenfirst + lenmiddle);
        }
 
        /*
         * Slow path to handle any remaining multibyte characters
         *
         * As we go, 'ptr' points to the beginning of the current
         * three-character string and 'endptr' points to just past it.
         */
        endptr = ptr + lenfirst + lenmiddle + lenlast;
        while (endptr <= str + bytelen)
        {
            compact_trigram(tptr, ptr, endptr - ptr);
            tptr++;
 
            /* Advance to the next character */
            if (endptr == str + bytelen)
                break;
            ptr += lenfirst;
            lenfirst = lenmiddle;
            lenmiddle = lenlast;
            lenlast = pg_mblen_unbounded(endptr);
            endptr += lenlast;
        }
    }
 
done:
    dst->length = tptr - GETARR(dst->datum);
    Assert(dst->length <= dst->allocated);
}
 
/*
 * Make array of trigrams without sorting and removing duplicate items.
 *
 * dst: where to return the array of trigrams.
 * str: source string, of length slen bytes.
 * bounds_p: where to return bounds of trigrams (if needed).
 */
static void
generate_trgm_only(growable_trgm_array *dst, char *str, int slen, TrgmBound **bounds_p)
{
    size_t      buflen;
    char       *buf;
    int         bytelen;
    char       *bword,
               *eword;
    TrgmBound  *bounds = NULL;
    int         bounds_allocated = 0;
 
    init_trgm_array(dst, slen);
 
    /*
     * If requested, allocate an array for the bounds, with the same size as
     * the trigram array.
     */
    if (bounds_p)
    {
        bounds_allocated = dst->allocated;
        bounds = *bounds_p = palloc0_array(TrgmBound, bounds_allocated);
    }
 
    if (slen + LPADDING + RPADDING < 3 || slen == 0)
        return;
 
    /*
     * Allocate a buffer for case-folded, blank-padded words.
     *
     * As an initial guess, allocate a buffer large enough to hold the
     * original string with padding, which is always enough when compiled with
     * !IGNORECASE.  If the case-folding produces a string longer than the
     * original, we'll grow the buffer.
     */
    buflen = (size_t) slen + 4;
    buf = (char *) palloc(buflen);
    if (LPADDING > 0)
    {
        *buf = ' ';
        if (LPADDING > 1)
            *(buf + 1) = ' ';
    }
 
    eword = str;
    while ((bword = find_word(eword, slen - (eword - str), &eword)) != NULL)
    {
        int         oldlen;
 
        /* Convert word to lower case before extracting trigrams from it */
#ifdef IGNORECASE
        {
            char       *lowered;
 
            lowered = str_tolower(bword, eword - bword, DEFAULT_COLLATION_OID);
            bytelen = strlen(lowered);
 
            /* grow the buffer if necessary */
            if (bytelen > buflen - 4)
            {
                pfree(buf);
                buflen = (size_t) bytelen + 4;
                buf = (char *) palloc(buflen);
                if (LPADDING > 0)
                {
                    *buf = ' ';
                    if (LPADDING > 1)
                        *(buf + 1) = ' ';
                }
            }
            memcpy(buf + LPADDING, lowered, bytelen);
            pfree(lowered);
        }
#else
        bytelen = eword - bword;
        memcpy(buf + LPADDING, bword, bytelen);
#endif
 
        buf[LPADDING + bytelen] = ' ';
        buf[LPADDING + bytelen + 1] = ' ';
 
        /* Calculate trigrams marking their bounds if needed */
        oldlen = dst->length;
        make_trigrams(dst, buf, bytelen + LPADDING + RPADDING);
        if (bounds)
        {
            if (bounds_allocated < dst->length)
            {
                bounds = *bounds_p = repalloc0_array(bounds, TrgmBound, bounds_allocated, dst->allocated);
                bounds_allocated = dst->allocated;
            }
 
            bounds[oldlen] |= TRGM_BOUND_LEFT;
            bounds[dst->length - 1] |= TRGM_BOUND_RIGHT;
        }
    }
 
    pfree(buf);
}
 
/*
 * Make array of trigrams with sorting and removing duplicate items.
 *
 * str: source string, of length slen bytes.
 *
 * Returns the sorted array of unique trigrams.
 */
TRGM *
generate_trgm(char *str, int slen)
{
    TRGM       *trg;
    growable_trgm_array arr;
    int         len;
 
    generate_trgm_only(&arr, str, slen, NULL);
    len = arr.length;
    trg = arr.datum;
    trg->flag = ARRKEY;
 
    /*
     * Make trigrams unique.
     */
    if (len > 1)
    {
        trigram_qsort(GETARR(trg), len);
        len = trigram_qunique(GETARR(trg), len);
    }
 
    SET_VARSIZE(trg, CALCGTSIZE(ARRKEY, len));
 
    return trg;
}
 
/*
 * Make array of positional trigrams from two trigram arrays trg1 and trg2.
 *
 * trg1: trigram array of search pattern, of length len1. trg1 is required
 *       word which positions don't matter and replaced with -1.
 * trg2: trigram array of text, of length len2. trg2 is haystack where we
 *       search and have to store its positions.
 *
 * Returns concatenated trigram array.
 */
static pos_trgm *
make_positional_trgm(trgm *trg1, int len1, trgm *trg2, int len2)
{
    pos_trgm   *result;
    int         i,
                len = len1 + len2;
 
    result = palloc_array(pos_trgm, len);
 
    for (i = 0; i < len1; i++)
    {
        memcpy(&result[i].trg, &trg1[i], sizeof(trgm));
        result[i].index = -1;
    }
 
    for (i = 0; i < len2; i++)
    {
        memcpy(&result[i + len1].trg, &trg2[i], sizeof(trgm));
        result[i + len1].index = i;
    }
 
    return result;
}
 
/*
 * Compare position trigrams: compare trigrams first and position second.
 */
static int
comp_ptrgm(const void *v1, const void *v2)
{
    const pos_trgm *p1 = (const pos_trgm *) v1;
    const pos_trgm *p2 = (const pos_trgm *) v2;
    int         cmp;
 
    cmp = CMPTRGM(p1->trg, p2->trg);
    if (cmp != 0)
        return cmp;
 
    return pg_cmp_s32(p1->index, p2->index);
}
 
/*
 * Iterative search function which calculates maximum similarity with word in
 * the string. Maximum similarity is only calculated only if the flag
 * WORD_SIMILARITY_CHECK_ONLY isn't set.
 *
 * trg2indexes: array which stores indexes of the array "found".
 * found: array which stores true of false values.
 * ulen1: count of unique trigrams of array "trg1".
 * len2: length of array "trg2" and array "trg2indexes".
 * len: length of the array "found".
 * flags: set of boolean flags parameterizing similarity calculation.
 * bounds: whether each trigram is left/right bound of word.
 *
 * Returns word similarity.
 */
static float4
iterate_word_similarity(int *trg2indexes,
                        bool *found,
                        int ulen1,
                        int len2,
                        int len,
                        uint8 flags,
                        TrgmBound *bounds)
{
    int        *lastpos,
                i,
                ulen2 = 0,
                count = 0,
                upper = -1,
                lower;
    float4      smlr_cur,
                smlr_max = 0.0f;
    double      threshold;
 
    Assert(bounds || !(flags & WORD_SIMILARITY_STRICT));
 
    /* Select appropriate threshold */
    threshold = (flags & WORD_SIMILARITY_STRICT) ?
        strict_word_similarity_threshold :
        word_similarity_threshold;
 
    /*
     * Consider first trigram as initial lower bound for strict word
     * similarity, or initialize it later with first trigram present for plain
     * word similarity.
     */
    lower = (flags & WORD_SIMILARITY_STRICT) ? 0 : -1;
 
    /* Memorise last position of each trigram */
    lastpos = palloc_array(int, len);
    memset(lastpos, -1, sizeof(int) * len);
 
    for (i = 0; i < len2; i++)
    {
        int         trgindex;
 
        CHECK_FOR_INTERRUPTS();
 
        /* Get index of next trigram */
        trgindex = trg2indexes[i];
 
        /* Update last position of this trigram */
        if (lower >= 0 || found[trgindex])
        {
            if (lastpos[trgindex] < 0)
            {
                ulen2++;
                if (found[trgindex])
                    count++;
            }
            lastpos[trgindex] = i;
        }
 
        /*
         * Adjust upper bound if trigram is upper bound of word for strict
         * word similarity, or if trigram is present in required substring for
         * plain word similarity
         */
        if ((flags & WORD_SIMILARITY_STRICT) ? (bounds[i] & TRGM_BOUND_RIGHT)
            : found[trgindex])
        {
            int         prev_lower,
                        tmp_ulen2,
                        tmp_lower,
                        tmp_count;
 
            upper = i;
            if (lower == -1)
            {
                lower = i;
                ulen2 = 1;
            }
 
            smlr_cur = CALCSML(count, ulen1, ulen2);
 
            /* Also try to adjust lower bound for greater similarity */
            tmp_count = count;
            tmp_ulen2 = ulen2;
            prev_lower = lower;
            for (tmp_lower = lower; tmp_lower <= upper; tmp_lower++)
            {
                float       smlr_tmp;
                int         tmp_trgindex;
 
                /*
                 * Adjust lower bound only if trigram is lower bound of word
                 * for strict word similarity, or consider every trigram as
                 * lower bound for plain word similarity.
                 */
                if (!(flags & WORD_SIMILARITY_STRICT)
                    || (bounds[tmp_lower] & TRGM_BOUND_LEFT))
                {
                    smlr_tmp = CALCSML(tmp_count, ulen1, tmp_ulen2);
                    if (smlr_tmp > smlr_cur)
                    {
                        smlr_cur = smlr_tmp;
                        ulen2 = tmp_ulen2;
                        lower = tmp_lower;
                        count = tmp_count;
                    }
 
                    /*
                     * If we only check that word similarity is greater than
                     * threshold we do not need to calculate a maximum
                     * similarity.
                     */
                    if ((flags & WORD_SIMILARITY_CHECK_ONLY)
                        && smlr_cur >= threshold)
                        break;
                }
 
                tmp_trgindex = trg2indexes[tmp_lower];
                if (lastpos[tmp_trgindex] == tmp_lower)
                {
                    tmp_ulen2--;
                    if (found[tmp_trgindex])
                        tmp_count--;
                }
            }
 
            smlr_max = Max(smlr_max, smlr_cur);
 
            /*
             * if we only check that word similarity is greater than threshold
             * we do not need to calculate a maximum similarity.
             */
            if ((flags & WORD_SIMILARITY_CHECK_ONLY) && smlr_max >= threshold)
                break;
 
            for (tmp_lower = prev_lower; tmp_lower < lower; tmp_lower++)
            {
                int         tmp_trgindex;
 
                tmp_trgindex = trg2indexes[tmp_lower];
                if (lastpos[tmp_trgindex] == tmp_lower)
                    lastpos[tmp_trgindex] = -1;
            }
        }
    }
 
    pfree(lastpos);
 
    return smlr_max;
}
 
/*
 * Calculate word similarity.
 * This function prepare two arrays: "trg2indexes" and "found". Then this arrays
 * are used to calculate word similarity using iterate_word_similarity().
 *
 * "trg2indexes" is array which stores indexes of the array "found".
 * In other words:
 * trg2indexes[j] = i;
 * found[i] = true (or false);
 * If found[i] == true then there is trigram trg2[j] in array "trg1".
 * If found[i] == false then there is not trigram trg2[j] in array "trg1".
 *
 * str1: search pattern string, of length slen1 bytes.
 * str2: text in which we are looking for a word, of length slen2 bytes.
 * flags: set of boolean flags parameterizing similarity calculation.
 *
 * Returns word similarity.
 */
static float4
calc_word_similarity(char *str1, int slen1, char *str2, int slen2,
                     uint8 flags)
{
    bool       *found;
    pos_trgm   *ptrg;
    growable_trgm_array trg1;
    growable_trgm_array trg2;
    int         len1,
                len2,
                len,
                i,
                j,
                ulen1;
    int        *trg2indexes;
    float4      result;
    TrgmBound  *bounds = NULL;
 
    /* Make positional trigrams */
 
    generate_trgm_only(&trg1, str1, slen1, NULL);
    len1 = trg1.length;
    generate_trgm_only(&trg2, str2, slen2, (flags & WORD_SIMILARITY_STRICT) ? &bounds : NULL);
    len2 = trg2.length;
 
    ptrg = make_positional_trgm(GETARR(trg1.datum), len1, GETARR(trg2.datum), len2);
    len = len1 + len2;
    qsort(ptrg, len, sizeof(pos_trgm), comp_ptrgm);
 
    pfree(trg1.datum);
    pfree(trg2.datum);
 
    /*
     * Merge positional trigrams array: enumerate each trigram and find its
     * presence in required word.
     */
    trg2indexes = palloc_array(int, len2);
    found = palloc0_array(bool, len);
 
    ulen1 = 0;
    j = 0;
    for (i = 0; i < len; i++)
    {
        if (i > 0)
        {
            int         cmp = CMPTRGM(ptrg[i - 1].trg, ptrg[i].trg);
 
            if (cmp != 0)
            {
                if (found[j])
                    ulen1++;
                j++;
            }
        }
 
        if (ptrg[i].index >= 0)
        {
            trg2indexes[ptrg[i].index] = j;
        }
        else
        {
            found[j] = true;
        }
    }
    if (found[j])
        ulen1++;
 
    /* Run iterative procedure to find maximum similarity with word */
    result = iterate_word_similarity(trg2indexes, found, ulen1, len2, len,
                                     flags, bounds);
 
    pfree(trg2indexes);
    pfree(found);
    pfree(ptrg);
 
    return result;
}
 
 
/*
 * Extract the next non-wildcard part of a search string, i.e. a word bounded
 * by '_' or '%' meta-characters, non-word characters or string end.
 *
 * str: source string, of length lenstr bytes (need not be null-terminated)
 * buf: where to return the substring (must be long enough)
 * *bytelen: receives byte length of the found substring
 *
 * Returns pointer to end+1 of the found substring in the source string.
 * Returns NULL if no word found (in which case buf, bytelen is not set)
 *
 * If the found word is bounded by non-word characters or string boundaries
 * then this function will include corresponding padding spaces into buf.
 */
static const char *
get_wildcard_part(const char *str, int lenstr,
                  char *buf, int *bytelen)
{
    const char *beginword = str;
    const char *endword;
    const char *endstr = str + lenstr;
    char       *s = buf;
    bool        in_leading_wildcard_meta = false;
    bool        in_trailing_wildcard_meta = false;
    bool        in_escape = false;
    int         clen;
 
    /*
     * Find the first word character, remembering whether preceding character
     * was wildcard meta-character.  Note that the in_escape state persists
     * from this loop to the next one, since we may exit at a word character
     * that is in_escape.
     */
    while (beginword < endstr)
    {
        clen = pg_mblen_range(beginword, endstr);
 
        if (in_escape)
        {
            if (ISWORDCHR(beginword, clen))
                break;
            in_escape = false;
            in_leading_wildcard_meta = false;
        }
        else
        {
            if (ISESCAPECHAR(beginword))
                in_escape = true;
            else if (ISWILDCARDCHAR(beginword))
                in_leading_wildcard_meta = true;
            else if (ISWORDCHR(beginword, clen))
                break;
            else
                in_leading_wildcard_meta = false;
        }
        beginword += clen;
    }
 
    /*
     * Handle string end.
     */
    if (beginword - str >= lenstr)
        return NULL;
 
    /*
     * Add left padding spaces if preceding character wasn't wildcard
     * meta-character.
     */
    if (!in_leading_wildcard_meta)
    {
        if (LPADDING > 0)
        {
            *s++ = ' ';
            if (LPADDING > 1)
                *s++ = ' ';
        }
    }
 
    /*
     * Copy data into buf until wildcard meta-character, non-word character or
     * string boundary.  Strip escapes during copy.
     */
    endword = beginword;
    while (endword < endstr)
    {
        clen = pg_mblen_range(endword, endstr);
        if (in_escape)
        {
            if (ISWORDCHR(endword, clen))
            {
                memcpy(s, endword, clen);
                s += clen;
            }
            else
            {
                /*
                 * Back up endword to the escape character when stopping at an
                 * escaped char, so that subsequent get_wildcard_part will
                 * restart from the escape character.  We assume here that
                 * escape chars are single-byte.
                 */
                endword--;
                break;
            }
            in_escape = false;
        }
        else
        {
            if (ISESCAPECHAR(endword))
                in_escape = true;
            else if (ISWILDCARDCHAR(endword))
            {
                in_trailing_wildcard_meta = true;
                break;
            }
            else if (ISWORDCHR(endword, clen))
            {
                memcpy(s, endword, clen);
                s += clen;
            }
            else
                break;
        }
        endword += clen;
    }
 
    /*
     * Add right padding spaces if next character isn't wildcard
     * meta-character.
     */
    if (!in_trailing_wildcard_meta)
    {
        if (RPADDING > 0)
        {
            *s++ = ' ';
            if (RPADDING > 1)
                *s++ = ' ';
        }
    }
 
    *bytelen = s - buf;
    return endword;
}
 
/*
 * Generates trigrams for wildcard search string.
 *
 * Returns array of trigrams that must occur in any string that matches the
 * wildcard string.  For example, given pattern "a%bcd%" the trigrams
 * " a", "bcd" would be extracted.
 */
TRGM *
generate_wildcard_trgm(const char *str, int slen)
{
    TRGM       *trg;
    growable_trgm_array arr;
    char       *buf;
    int         len,
                bytelen;
    const char *eword;
 
    if (slen + LPADDING + RPADDING < 3 || slen == 0)
    {
        trg = (TRGM *) palloc(TRGMHDRSIZE);
        trg->flag = ARRKEY;
        SET_VARSIZE(trg, TRGMHDRSIZE);
        return trg;
    }
 
    init_trgm_array(&arr, slen);
 
    /* Allocate a buffer for blank-padded, but not yet case-folded, words */
    buf = palloc_array(char, slen + 4);
 
    /*
     * Extract trigrams from each substring extracted by get_wildcard_part.
     */
    eword = str;
    while ((eword = get_wildcard_part(eword, slen - (eword - str),
                                      buf, &bytelen)) != NULL)
    {
        char       *word;
 
#ifdef IGNORECASE
        word = str_tolower(buf, bytelen, DEFAULT_COLLATION_OID);
        bytelen = strlen(word);
#else
        word = buf;
#endif
 
        /*
         * count trigrams
         */
        make_trigrams(&arr, word, bytelen);
 
#ifdef IGNORECASE
        pfree(word);
#endif
    }
 
    pfree(buf);
 
    /*
     * Make trigrams unique.
     */
    trg = arr.datum;
    len = arr.length;
    if (len > 1)
    {
        trigram_qsort(GETARR(trg), len);
        len = trigram_qunique(GETARR(trg), len);
    }
 
    trg->flag = ARRKEY;
    SET_VARSIZE(trg, CALCGTSIZE(ARRKEY, len));
 
    return trg;
}
 
uint32
trgm2int(trgm *ptr)
{
    uint32      val = 0;
 
    val |= *(((unsigned char *) ptr));
    val <<= 8;
    val |= *(((unsigned char *) ptr) + 1);
    val <<= 8;
    val |= *(((unsigned char *) ptr) + 2);
 
    return val;
}
 
Datum
show_trgm(PG_FUNCTION_ARGS)
{
    text       *in = PG_GETARG_TEXT_PP(0);
    TRGM       *trg;
    Datum      *d;
    ArrayType  *a;
    trgm       *ptr;
    int         i;
 
    trg = generate_trgm(VARDATA_ANY(in), VARSIZE_ANY_EXHDR(in));
    d = palloc_array(Datum, 1 + ARRNELEM(trg));
 
    for (i = 0, ptr = GETARR(trg); i < ARRNELEM(trg); i++, ptr++)
    {
        text       *item = (text *) palloc(VARHDRSZ + Max(12, pg_database_encoding_max_length() * 3));
 
        if (pg_database_encoding_max_length() > 1 && !ISPRINTABLETRGM(ptr))
        {
            snprintf(VARDATA(item), 12, "0x%06x", trgm2int(ptr));
            SET_VARSIZE(item, VARHDRSZ + strlen(VARDATA(item)));
        }
        else
        {
            SET_VARSIZE(item, VARHDRSZ + 3);
            CPTRGM(VARDATA(item), ptr);
        }
        d[i] = PointerGetDatum(item);
    }
 
    a = construct_array_builtin(d, ARRNELEM(trg), TEXTOID);
 
    for (i = 0; i < ARRNELEM(trg); i++)
        pfree(DatumGetPointer(d[i]));
 
    pfree(d);
    pfree(trg);
    PG_FREE_IF_COPY(in, 0);
 
    PG_RETURN_POINTER(a);
}
 
float4
cnt_sml(TRGM *trg1, TRGM *trg2, bool inexact)
{
    trgm       *ptr1,
               *ptr2;
    int         count = 0;
    int         len1,
                len2;
 
    ptr1 = GETARR(trg1);
    ptr2 = GETARR(trg2);
 
    len1 = ARRNELEM(trg1);
    len2 = ARRNELEM(trg2);
 
    /* explicit test is needed to avoid 0/0 division when both lengths are 0 */
    if (len1 <= 0 || len2 <= 0)
        return (float4) 0.0;
 
    while (ptr1 - GETARR(trg1) < len1 && ptr2 - GETARR(trg2) < len2)
    {
        int         res = CMPTRGM(ptr1, ptr2);
 
        if (res < 0)
            ptr1++;
        else if (res > 0)
            ptr2++;
        else
        {
            ptr1++;
            ptr2++;
            count++;
        }
    }
 
    /*
     * If inexact then len2 is equal to count, because we don't know actual
     * length of second string in inexact search and we can assume that count
     * is a lower bound of len2.
     */
    return CALCSML(count, len1, inexact ? count : len2);
}
 
 
/*
 * Returns whether trg2 contains all trigrams in trg1.
 * This relies on the trigram arrays being sorted.
 */
bool
trgm_contained_by(TRGM *trg1, TRGM *trg2)
{
    trgm       *ptr1,
               *ptr2;
    int         len1,
                len2;
 
    ptr1 = GETARR(trg1);
    ptr2 = GETARR(trg2);
 
    len1 = ARRNELEM(trg1);
    len2 = ARRNELEM(trg2);
 
    while (ptr1 - GETARR(trg1) < len1 && ptr2 - GETARR(trg2) < len2)
    {
        int         res = CMPTRGM(ptr1, ptr2);
 
        if (res < 0)
            return false;
        else if (res > 0)
            ptr2++;
        else
        {
            ptr1++;
            ptr2++;
        }
    }
    if (ptr1 - GETARR(trg1) < len1)
        return false;
    else
        return true;
}
 
/*
 * Return a palloc'd boolean array showing, for each trigram in "query",
 * whether it is present in the trigram array "key".
 * This relies on the "key" array being sorted, but "query" need not be.
 */
bool *
trgm_presence_map(TRGM *query, TRGM *key)
{
    bool       *result;
    trgm       *ptrq = GETARR(query),
               *ptrk = GETARR(key);
    int         lenq = ARRNELEM(query),
                lenk = ARRNELEM(key),
                i;
 
    result = palloc0_array(bool, lenq);
 
    /* for each query trigram, do a binary search in the key array */
    for (i = 0; i < lenq; i++)
    {
        int         lo = 0;
        int         hi = lenk;
 
        while (lo < hi)
        {
            int         mid = (lo + hi) / 2;
            int         res = CMPTRGM(ptrq, ptrk + mid);
 
            if (res < 0)
                hi = mid;
            else if (res > 0)
                lo = mid + 1;
            else
            {
                result[i] = true;
                break;
            }
        }
        ptrq++;
    }
 
    return result;
}
 
Datum
similarity(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    TRGM       *trg1,
               *trg2;
    float4      res;
 
    trg1 = generate_trgm(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1));
    trg2 = generate_trgm(VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2));
 
    res = cnt_sml(trg1, trg2, false);
 
    pfree(trg1);
    pfree(trg2);
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
 
    PG_RETURN_FLOAT4(res);
}
 
Datum
word_similarity(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               0);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_FLOAT4(res);
}
 
Datum
strict_word_similarity(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               WORD_SIMILARITY_STRICT);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_FLOAT4(res);
}
 
Datum
similarity_dist(PG_FUNCTION_ARGS)
{
    float4      res = DatumGetFloat4(DirectFunctionCall2(similarity,
                                                         PG_GETARG_DATUM(0),
                                                         PG_GETARG_DATUM(1)));
 
    PG_RETURN_FLOAT4(1.0 - res);
}
 
Datum
similarity_op(PG_FUNCTION_ARGS)
{
    float4      res = DatumGetFloat4(DirectFunctionCall2(similarity,
                                                         PG_GETARG_DATUM(0),
                                                         PG_GETARG_DATUM(1)));
 
    PG_RETURN_BOOL(res >= similarity_threshold);
}
 
Datum
word_similarity_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               WORD_SIMILARITY_CHECK_ONLY);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_BOOL(res >= word_similarity_threshold);
}
 
Datum
word_similarity_commutator_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               WORD_SIMILARITY_CHECK_ONLY);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_BOOL(res >= word_similarity_threshold);
}
 
Datum
word_similarity_dist_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               0);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_FLOAT4(1.0 - res);
}
 
Datum
word_similarity_dist_commutator_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               0);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_FLOAT4(1.0 - res);
}
 
Datum
strict_word_similarity_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               WORD_SIMILARITY_CHECK_ONLY | WORD_SIMILARITY_STRICT);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_BOOL(res >= strict_word_similarity_threshold);
}
 
Datum
strict_word_similarity_commutator_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               WORD_SIMILARITY_CHECK_ONLY | WORD_SIMILARITY_STRICT);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_BOOL(res >= strict_word_similarity_threshold);
}
 
Datum
strict_word_similarity_dist_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               WORD_SIMILARITY_STRICT);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_FLOAT4(1.0 - res);
}
 
Datum
strict_word_similarity_dist_commutator_op(PG_FUNCTION_ARGS)
{
    text       *in1 = PG_GETARG_TEXT_PP(0);
    text       *in2 = PG_GETARG_TEXT_PP(1);
    float4      res;
 
    res = calc_word_similarity(VARDATA_ANY(in2), VARSIZE_ANY_EXHDR(in2),
                               VARDATA_ANY(in1), VARSIZE_ANY_EXHDR(in1),
                               WORD_SIMILARITY_STRICT);
 
    PG_FREE_IF_COPY(in1, 0);
    PG_FREE_IF_COPY(in2, 1);
    PG_RETURN_FLOAT4(1.0 - res);
}