unicode_norm.c

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/*-------------------------------------------------------------------------
 * unicode_norm.c
 *      Normalize a Unicode string
 *
 * This implements Unicode normalization, per the documentation at
 * https://www.unicode.org/reports/tr15/.
 *
 * Portions Copyright (c) 2017-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/common/unicode_norm.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#include "common/unicode_norm.h"
#ifndef FRONTEND
#include "common/unicode_norm_hashfunc.h"
#include "common/unicode_normprops_table.h"
#include "port/pg_bswap.h"
#include "utils/memutils.h"
#else
#include "common/unicode_norm_table.h"
#endif
 
#ifndef FRONTEND
#define ALLOC(size) palloc(size)
#define FREE(size) pfree(size)
#else
#define ALLOC(size) malloc(size)
#define FREE(size) free(size)
#endif
 
/* Constants for calculations with Hangul characters */
#define SBASE       0xAC00      /* U+AC00 */
#define LBASE       0x1100      /* U+1100 */
#define VBASE       0x1161      /* U+1161 */
#define TBASE       0x11A7      /* U+11A7 */
#define LCOUNT      19
#define VCOUNT      21
#define TCOUNT      28
#define NCOUNT      VCOUNT * TCOUNT
#define SCOUNT      LCOUNT * NCOUNT
 
#ifdef FRONTEND
/* comparison routine for bsearch() of decomposition lookup table. */
static int
conv_compare(const void *p1, const void *p2)
{
    uint32      v1,
                v2;
 
    v1 = *(const uint32 *) p1;
    v2 = ((const pg_unicode_decomposition *) p2)->codepoint;
    return (v1 > v2) ? 1 : ((v1 == v2) ? 0 : -1);
}
 
#endif
 
/*
 * get_code_entry
 *
 * Get the entry corresponding to code in the decomposition lookup table.
 * The backend version of this code uses a perfect hash function for the
 * lookup, while the frontend version uses a binary search.
 */
static const pg_unicode_decomposition *
get_code_entry(char32_t code)
{
#ifndef FRONTEND
    int         h;
    uint32      hashkey;
    pg_unicode_decompinfo decompinfo = UnicodeDecompInfo;
 
    /*
     * Compute the hash function. The hash key is the codepoint with the bytes
     * in network order.
     */
    hashkey = pg_hton32(code);
    h = decompinfo.hash(&hashkey);
 
    /* An out-of-range result implies no match */
    if (h < 0 || h >= decompinfo.num_decomps)
        return NULL;
 
    /*
     * Since it's a perfect hash, we need only match to the specific codepoint
     * it identifies.
     */
    if (code != decompinfo.decomps[h].codepoint)
        return NULL;
 
    /* Success! */
    return &decompinfo.decomps[h];
#else
    return bsearch(&(code),
                   UnicodeDecompMain,
                   lengthof(UnicodeDecompMain),
                   sizeof(pg_unicode_decomposition),
                   conv_compare);
#endif
}
 
/*
 * Get the combining class of the given codepoint.
 */
static uint8
get_canonical_class(char32_t code)
{
    const pg_unicode_decomposition *entry = get_code_entry(code);
 
    /*
     * If no entries are found, the character used is either a Hangul
     * character or a character with a class of 0 and no decompositions.
     */
    if (!entry)
        return 0;
    else
        return entry->comb_class;
}
 
/*
 * Given a decomposition entry looked up earlier, get the decomposed
 * characters.
 *
 * Note: the returned pointer can point to statically allocated buffer, and
 * is only valid until next call to this function!
 */
static const char32_t *
get_code_decomposition(const pg_unicode_decomposition *entry, int *dec_size)
{
    static char32_t x;
 
    if (DECOMPOSITION_IS_INLINE(entry))
    {
        Assert(DECOMPOSITION_SIZE(entry) == 1);
        x = (char32_t) entry->dec_index;
        *dec_size = 1;
        return &x;
    }
    else
    {
        *dec_size = DECOMPOSITION_SIZE(entry);
        return &UnicodeDecomp_codepoints[entry->dec_index];
    }
}
 
/*
 * Calculate how many characters a given character will decompose to.
 *
 * This needs to recurse, if the character decomposes into characters that
 * are, in turn, decomposable.
 */
static int
get_decomposed_size(char32_t code, bool compat)
{
    const pg_unicode_decomposition *entry;
    int         size = 0;
    int         i;
    const uint32 *decomp;
    int         dec_size;
 
    /*
     * Fast path for Hangul characters not stored in tables to save memory as
     * decomposition is algorithmic. See
     * https://www.unicode.org/reports/tr15/tr15-18.html, annex 10 for details
     * on the matter.
     */
    if (code >= SBASE && code < SBASE + SCOUNT)
    {
        uint32      tindex,
                    sindex;
 
        sindex = code - SBASE;
        tindex = sindex % TCOUNT;
 
        if (tindex != 0)
            return 3;
        return 2;
    }
 
    entry = get_code_entry(code);
 
    /*
     * Just count current code if no other decompositions.  A NULL entry is
     * equivalent to a character with class 0 and no decompositions.
     */
    if (entry == NULL || DECOMPOSITION_SIZE(entry) == 0 ||
        (!compat && DECOMPOSITION_IS_COMPAT(entry)))
        return 1;
 
    /*
     * If this entry has other decomposition codes look at them as well. First
     * get its decomposition in the list of tables available.
     */
    decomp = get_code_decomposition(entry, &dec_size);
    for (i = 0; i < dec_size; i++)
    {
        uint32      lcode = decomp[i];
 
        size += get_decomposed_size(lcode, compat);
    }
 
    return size;
}
 
/*
 * Recompose a set of characters. For hangul characters, the calculation
 * is algorithmic. For others, an inverse lookup at the decomposition
 * table is necessary. Returns true if a recomposition can be done, and
 * false otherwise.
 */
static bool
recompose_code(uint32 start, uint32 code, uint32 *result)
{
    /*
     * Handle Hangul characters algorithmically, per the Unicode spec.
     *
     * Check if two current characters are L and V.
     */
    if (start >= LBASE && start < LBASE + LCOUNT &&
        code >= VBASE && code < VBASE + VCOUNT)
    {
        /* make syllable of form LV */
        uint32      lindex = start - LBASE;
        uint32      vindex = code - VBASE;
 
        *result = SBASE + (lindex * VCOUNT + vindex) * TCOUNT;
        return true;
    }
    /* Check if two current characters are LV and T */
    else if (start >= SBASE && start < (SBASE + SCOUNT) &&
             ((start - SBASE) % TCOUNT) == 0 &&
             code >= TBASE && code < (TBASE + TCOUNT))
    {
        /* make syllable of form LVT */
        uint32      tindex = code - TBASE;
 
        *result = start + tindex;
        return true;
    }
    else
    {
        const pg_unicode_decomposition *entry;
 
        /*
         * Do an inverse lookup of the decomposition tables to see if anything
         * matches. The comparison just needs to be a perfect match on the
         * sub-table of size two, because the start character has already been
         * recomposed partially.  This lookup uses a perfect hash function for
         * the backend code.
         */
#ifndef FRONTEND
 
        int         h,
                    inv_lookup_index;
        uint64      hashkey;
        pg_unicode_recompinfo recompinfo = UnicodeRecompInfo;
 
        /*
         * Compute the hash function. The hash key is formed by concatenating
         * bytes of the two codepoints in network order. See also
         * src/common/unicode/generate-unicode_norm_table.pl.
         */
        hashkey = pg_hton64(((uint64) start << 32) | (uint64) code);
        h = recompinfo.hash(&hashkey);
 
        /* An out-of-range result implies no match */
        if (h < 0 || h >= recompinfo.num_recomps)
            return false;
 
        inv_lookup_index = recompinfo.inverse_lookup[h];
        entry = &UnicodeDecompMain[inv_lookup_index];
 
        if (start == UnicodeDecomp_codepoints[entry->dec_index] &&
            code == UnicodeDecomp_codepoints[entry->dec_index + 1])
        {
            *result = entry->codepoint;
            return true;
        }
 
#else
 
        int         i;
 
        for (i = 0; i < lengthof(UnicodeDecompMain); i++)
        {
            entry = &UnicodeDecompMain[i];
 
            if (DECOMPOSITION_SIZE(entry) != 2)
                continue;
 
            if (DECOMPOSITION_NO_COMPOSE(entry))
                continue;
 
            if (start == UnicodeDecomp_codepoints[entry->dec_index] &&
                code == UnicodeDecomp_codepoints[entry->dec_index + 1])
            {
                *result = entry->codepoint;
                return true;
            }
        }
#endif                          /* !FRONTEND */
    }
 
    return false;
}
 
/*
 * Decompose the given code into the array given by caller. The
 * decomposition begins at the position given by caller, saving one
 * lookup on the decomposition table. The current position needs to be
 * updated here to let the caller know from where to continue filling
 * in the array result.
 */
static void
decompose_code(char32_t code, bool compat, char32_t **result, int *current)
{
    const pg_unicode_decomposition *entry;
    int         i;
    const uint32 *decomp;
    int         dec_size;
 
    /*
     * Fast path for Hangul characters not stored in tables to save memory as
     * decomposition is algorithmic. See
     * https://www.unicode.org/reports/tr15/tr15-18.html, annex 10 for details
     * on the matter.
     */
    if (code >= SBASE && code < SBASE + SCOUNT)
    {
        uint32      l,
                    v,
                    tindex,
                    sindex;
        char32_t   *res = *result;
 
        sindex = code - SBASE;
        l = LBASE + sindex / (VCOUNT * TCOUNT);
        v = VBASE + (sindex % (VCOUNT * TCOUNT)) / TCOUNT;
        tindex = sindex % TCOUNT;
 
        res[*current] = l;
        (*current)++;
        res[*current] = v;
        (*current)++;
 
        if (tindex != 0)
        {
            res[*current] = TBASE + tindex;
            (*current)++;
        }
 
        return;
    }
 
    entry = get_code_entry(code);
 
    /*
     * Just fill in with the current decomposition if there are no
     * decomposition codes to recurse to.  A NULL entry is equivalent to a
     * character with class 0 and no decompositions, so just leave also in
     * this case.
     */
    if (entry == NULL || DECOMPOSITION_SIZE(entry) == 0 ||
        (!compat && DECOMPOSITION_IS_COMPAT(entry)))
    {
        char32_t   *res = *result;
 
        res[*current] = code;
        (*current)++;
        return;
    }
 
    /*
     * If this entry has other decomposition codes look at them as well.
     */
    decomp = get_code_decomposition(entry, &dec_size);
    for (i = 0; i < dec_size; i++)
    {
        char32_t    lcode = (char32_t) decomp[i];
 
        /* Leave if no more decompositions */
        decompose_code(lcode, compat, result, current);
    }
}
 
/*
 * unicode_normalize - Normalize a Unicode string to the specified form.
 *
 * The input is a 0-terminated array of codepoints.
 *
 * In frontend, returns a 0-terminated array of codepoints, allocated with
 * malloc. Or NULL if we run out of memory. In backend, the returned
 * string is palloc'd instead, and OOM is reported with ereport().
 */
char32_t *
unicode_normalize(UnicodeNormalizationForm form, const char32_t *input)
{
    bool        compat = (form == UNICODE_NFKC || form == UNICODE_NFKD);
    bool        recompose = (form == UNICODE_NFC || form == UNICODE_NFKC);
    char32_t   *decomp_chars;
    char32_t   *recomp_chars;
    int         decomp_size,
                current_size;
    int         count;
    const char32_t *p;
 
    /* variables for recomposition */
    int         last_class;
    int         starter_pos;
    int         target_pos;
    uint32      starter_ch;
 
    /* First, do character decomposition */
 
    /*
     * Calculate how many characters long the decomposed version will be.
     *
     * Some characters decompose to quite a few code points, so that the
     * decomposed version's size could overrun MaxAllocSize, and even 32-bit
     * size_t, even though the input string presumably fits in that.  In
     * frontend we want to just return NULL in that case, so monitor the sum
     * and exit early once we'd need more than MaxAllocSize bytes.
     */
    decomp_size = 0;
    for (p = input; *p; p++)
    {
        decomp_size += get_decomposed_size(*p, compat);
        if (unlikely(decomp_size > MaxAllocSize / sizeof(char32_t)))
        {
#ifndef FRONTEND
            /* Exit loop and let palloc() throw error below */
            break;
#else
            /* Just return NULL with no explicit error */
            return NULL;
#endif
        }
    }
 
    decomp_chars = (char32_t *) ALLOC((decomp_size + 1) * sizeof(char32_t));
    if (decomp_chars == NULL)
        return NULL;
 
    /*
     * Now fill in each entry recursively. This needs a second pass on the
     * decomposition table.
     */
    current_size = 0;
    for (p = input; *p; p++)
        decompose_code(*p, compat, &decomp_chars, &current_size);
    decomp_chars[decomp_size] = '\0';
    Assert(decomp_size == current_size);
 
    /* Leave if there is nothing to decompose */
    if (decomp_size == 0)
        return decomp_chars;
 
    /*
     * Now apply canonical ordering.
     */
    for (count = 1; count < decomp_size; count++)
    {
        char32_t    prev = decomp_chars[count - 1];
        char32_t    next = decomp_chars[count];
        char32_t    tmp;
        const uint8 prevClass = get_canonical_class(prev);
        const uint8 nextClass = get_canonical_class(next);
 
        /*
         * Per Unicode (https://www.unicode.org/reports/tr15/tr15-18.html)
         * annex 4, a sequence of two adjacent characters in a string is an
         * exchangeable pair if the combining class (from the Unicode
         * Character Database) for the first character is greater than the
         * combining class for the second, and the second is not a starter.  A
         * character is a starter if its combining class is 0.
         */
        if (prevClass == 0 || nextClass == 0)
            continue;
 
        if (prevClass <= nextClass)
            continue;
 
        /* exchange can happen */
        tmp = decomp_chars[count - 1];
        decomp_chars[count - 1] = decomp_chars[count];
        decomp_chars[count] = tmp;
 
        /* backtrack to check again */
        if (count > 1)
            count -= 2;
    }
 
    if (!recompose)
        return decomp_chars;
 
    /*
     * The last phase of NFC and NFKC is the recomposition of the reordered
     * Unicode string using combining classes. The recomposed string cannot be
     * longer than the decomposed one, so make the allocation of the output
     * string based on that assumption.
     */
    recomp_chars = (char32_t *) ALLOC((decomp_size + 1) * sizeof(char32_t));
    if (!recomp_chars)
    {
        FREE(decomp_chars);
        return NULL;
    }
 
    last_class = -1;            /* this eliminates a special check */
    starter_pos = 0;
    target_pos = 1;
    starter_ch = recomp_chars[0] = decomp_chars[0];
 
    for (count = 1; count < decomp_size; count++)
    {
        char32_t    ch = decomp_chars[count];
        int         ch_class = get_canonical_class(ch);
        char32_t    composite;
 
        if (last_class < ch_class &&
            recompose_code(starter_ch, ch, &composite))
        {
            recomp_chars[starter_pos] = composite;
            starter_ch = composite;
        }
        else if (ch_class == 0)
        {
            starter_pos = target_pos;
            starter_ch = ch;
            last_class = -1;
            recomp_chars[target_pos++] = ch;
        }
        else
        {
            last_class = ch_class;
            recomp_chars[target_pos++] = ch;
        }
    }
    recomp_chars[target_pos] = (char32_t) '\0';
 
    FREE(decomp_chars);
 
    return recomp_chars;
}
 
/*
 * Normalization "quick check" algorithm; see
 * <http://www.unicode.org/reports/tr15/#Detecting_Normalization_Forms>
 */
 
/* We only need this in the backend. */
#ifndef FRONTEND
 
static const pg_unicode_normprops *
qc_hash_lookup(char32_t ch, const pg_unicode_norminfo *norminfo)
{
    int         h;
    uint32      hashkey;
 
    /*
     * Compute the hash function. The hash key is the codepoint with the bytes
     * in network order.
     */
    hashkey = pg_hton32(ch);
    h = norminfo->hash(&hashkey);
 
    /* An out-of-range result implies no match */
    if (h < 0 || h >= norminfo->num_normprops)
        return NULL;
 
    /*
     * Since it's a perfect hash, we need only match to the specific codepoint
     * it identifies.
     */
    if (ch != norminfo->normprops[h].codepoint)
        return NULL;
 
    /* Success! */
    return &norminfo->normprops[h];
}
 
/*
 * Look up the normalization quick check character property
 */
static UnicodeNormalizationQC
qc_is_allowed(UnicodeNormalizationForm form, char32_t ch)
{
    const pg_unicode_normprops *found = NULL;
 
    switch (form)
    {
        case UNICODE_NFC:
            found = qc_hash_lookup(ch, &UnicodeNormInfo_NFC_QC);
            break;
        case UNICODE_NFKC:
            found = qc_hash_lookup(ch, &UnicodeNormInfo_NFKC_QC);
            break;
        default:
            Assert(false);
            break;
    }
 
    if (found)
        return found->quickcheck;
    else
        return UNICODE_NORM_QC_YES;
}
 
UnicodeNormalizationQC
unicode_is_normalized_quickcheck(UnicodeNormalizationForm form, const char32_t *input)
{
    uint8       lastCanonicalClass = 0;
    UnicodeNormalizationQC result = UNICODE_NORM_QC_YES;
 
    /*
     * For the "D" forms, we don't run the quickcheck.  We don't include the
     * lookup tables for those because they are huge, checking for these
     * particular forms is less common, and running the slow path is faster
     * for the "D" forms than the "C" forms because you don't need to
     * recompose, which is slow.
     */
    if (form == UNICODE_NFD || form == UNICODE_NFKD)
        return UNICODE_NORM_QC_MAYBE;
 
    for (const char32_t *p = input; *p; p++)
    {
        char32_t    ch = *p;
        uint8       canonicalClass;
        UnicodeNormalizationQC check;
 
        canonicalClass = get_canonical_class(ch);
        if (lastCanonicalClass > canonicalClass && canonicalClass != 0)
            return UNICODE_NORM_QC_NO;
 
        check = qc_is_allowed(form, ch);
        if (check == UNICODE_NORM_QC_NO)
            return UNICODE_NORM_QC_NO;
        else if (check == UNICODE_NORM_QC_MAYBE)
            result = UNICODE_NORM_QC_MAYBE;
 
        lastCanonicalClass = canonicalClass;
    }
    return result;
}
 
#endif                          /* !FRONTEND */