unicode_case.c

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/*-------------------------------------------------------------------------
 * unicode_case.c
 *      Unicode case mapping and case conversion.
 *
 * Portions Copyright (c) 2017-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/common/unicode_case.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#include "common/unicode_case.h"
#include "common/unicode_case_table.h"
#include "common/unicode_category.h"
#include "mb/pg_wchar.h"
 
enum CaseMapResult
{
    CASEMAP_SELF,
    CASEMAP_SIMPLE,
    CASEMAP_SPECIAL,
};
 
/*
 * Map for each case kind.
 */
static const char32_t *const casekind_map[NCaseKind] =
{
    [CaseLower] = case_map_lower,
    [CaseTitle] = case_map_title,
    [CaseUpper] = case_map_upper,
    [CaseFold] = case_map_fold,
};
 
static char32_t find_case_map(char32_t ucs, const char32_t *map);
static size_t convert_case(char *dst, size_t dstsize, const char *src, size_t srclen,
                           CaseKind str_casekind, bool full, WordBoundaryNext wbnext,
                           void *wbstate);
static enum CaseMapResult casemap(char32_t u1, CaseKind casekind, bool full,
                                  const char *src, size_t srclen, size_t srcoff,
                                  char32_t *simple, const char32_t **special);
 
char32_t
unicode_lowercase_simple(char32_t code)
{
    char32_t    cp = find_case_map(code, case_map_lower);
 
    return cp != 0 ? cp : code;
}
 
char32_t
unicode_titlecase_simple(char32_t code)
{
    char32_t    cp = find_case_map(code, case_map_title);
 
    return cp != 0 ? cp : code;
}
 
char32_t
unicode_uppercase_simple(char32_t code)
{
    char32_t    cp = find_case_map(code, case_map_upper);
 
    return cp != 0 ? cp : code;
}
 
char32_t
unicode_casefold_simple(char32_t code)
{
    char32_t    cp = find_case_map(code, case_map_fold);
 
    return cp != 0 ? cp : code;
}
 
/*
 * unicode_strlower()
 *
 * Convert src to lowercase, and return the result length (not including
 * terminating NUL).
 *
 * String src must be encoded in UTF-8.
 *
 * Result string is stored in dst, truncating if larger than dstsize. If
 * dstsize is greater than the result length, dst will be NUL-terminated;
 * otherwise not.
 *
 * If dstsize is zero, dst may be NULL. This is useful for calculating the
 * required buffer size before allocating.
 *
 * If full is true, use special case mappings if available and if the
 * conditions are satisfied.
 */
size_t
unicode_strlower(char *dst, size_t dstsize, const char *src, size_t srclen,
                 bool full)
{
    return convert_case(dst, dstsize, src, srclen, CaseLower, full, NULL,
                        NULL);
}
 
/*
 * unicode_strtitle()
 *
 * Convert src to titlecase, and return the result length (not including
 * terminating NUL).
 *
 * String src must be encoded in UTF-8.
 *
 * Result string is stored in dst, truncating if larger than dstsize. If
 * dstsize is greater than the result length, dst will be NUL-terminated;
 * otherwise not.
 *
 * If dstsize is zero, dst may be NULL. This is useful for calculating the
 * required buffer size before allocating.
 *
 * If full is true, use special case mappings if available and if the
 * conditions are satisfied. Otherwise, use only simple mappings and use
 * uppercase instead of titlecase.
 *
 * Titlecasing requires knowledge about word boundaries, which is provided by
 * the callback wbnext. A word boundary is the offset of the start of a word
 * or the offset of the character immediately following a word.
 *
 * The caller is expected to initialize and free the callback state
 * wbstate. The callback should first return offset 0 for the first boundary;
 * then the offset of each subsequent word boundary; then the total length of
 * the string to indicate the final boundary.
 */
size_t
unicode_strtitle(char *dst, size_t dstsize, const char *src, size_t srclen,
                 bool full, WordBoundaryNext wbnext, void *wbstate)
{
    return convert_case(dst, dstsize, src, srclen, CaseTitle, full, wbnext,
                        wbstate);
}
 
/*
 * unicode_strupper()
 *
 * Convert src to uppercase, and return the result length (not including
 * terminating NUL).
 *
 * String src must be encoded in UTF-8.
 *
 * Result string is stored in dst, truncating if larger than dstsize. If
 * dstsize is greater than the result length, dst will be NUL-terminated;
 * otherwise not.
 *
 * If dstsize is zero, dst may be NULL. This is useful for calculating the
 * required buffer size before allocating.
 *
 * If full is true, use special case mappings if available and if the
 * conditions are satisfied.
 */
size_t
unicode_strupper(char *dst, size_t dstsize, const char *src, size_t srclen,
                 bool full)
{
    return convert_case(dst, dstsize, src, srclen, CaseUpper, full, NULL,
                        NULL);
}
 
/*
 * unicode_strfold()
 *
 * Case fold src, and return the result length (not including terminating
 * NUL).
 *
 * String src must be encoded in UTF-8.
 *
 * Result string is stored in dst, truncating if larger than dstsize. If
 * dstsize is greater than the result length, dst will be NUL-terminated;
 * otherwise not.
 *
 * If dstsize is zero, dst may be NULL. This is useful for calculating the
 * required buffer size before allocating.
 */
size_t
unicode_strfold(char *dst, size_t dstsize, const char *src, size_t srclen,
                bool full)
{
    return convert_case(dst, dstsize, src, srclen, CaseFold, full, NULL,
                        NULL);
}
 
/*
 * Implement Unicode Default Case Conversion algorithm.
 *
 * If str_casekind is CaseLower or CaseUpper, map each character in the string
 * for which a mapping is available.
 *
 * If str_casekind is CaseTitle, maps characters found on a word boundary to
 * titlecase (or uppercase if full is false) and other characters to
 * lowercase. NB: does not currently implement the Unicode behavior in which
 * the word boundary is adjusted to the next Cased character. That behavior
 * could be implemented as an option, but it doesn't match the default
 * behavior of ICU, nor does it match the documented behavior of INITCAP().
 *
 * If full is true, use special mappings for relevant characters, which can
 * map a single codepoint to multiple codepoints, or depend on conditions.
 */
static size_t
convert_case(char *dst, size_t dstsize, const char *src, size_t srclen,
             CaseKind str_casekind, bool full, WordBoundaryNext wbnext,
             void *wbstate)
{
    /* character CaseKind varies while titlecasing */
    CaseKind    chr_casekind = str_casekind;
    size_t      srcoff = 0;
    size_t      result_len = 0;
    size_t      boundary = 0;
 
    Assert((str_casekind == CaseTitle && wbnext && wbstate) ||
           (str_casekind != CaseTitle && !wbnext && !wbstate));
 
    if (str_casekind == CaseTitle)
    {
        boundary = wbnext(wbstate);
        Assert(boundary == 0);  /* start of text is always a boundary */
    }
 
    while (srcoff < srclen)
    {
        char32_t    u1 = utf8_to_unicode((const unsigned char *) src + srcoff);
        int         u1len = unicode_utf8len(u1);
        char32_t    simple = 0;
        const char32_t *special = NULL;
        enum CaseMapResult casemap_result;
 
        if (str_casekind == CaseTitle)
        {
            if (srcoff == boundary)
            {
                chr_casekind = full ? CaseTitle : CaseUpper;
                boundary = wbnext(wbstate);
            }
            else
                chr_casekind = CaseLower;
        }
 
        casemap_result = casemap(u1, chr_casekind, full, src, srclen, srcoff,
                                 &simple, &special);
 
        switch (casemap_result)
        {
            case CASEMAP_SELF:
                /* no mapping; copy bytes from src */
                Assert(simple == 0);
                Assert(special == NULL);
                if (result_len + u1len <= dstsize)
                    memcpy(dst + result_len, src + srcoff, u1len);
 
                result_len += u1len;
                break;
            case CASEMAP_SIMPLE:
                {
                    /* replace with single character */
                    char32_t    u2 = simple;
                    char32_t    u2len = unicode_utf8len(u2);
 
                    Assert(special == NULL);
                    if (result_len + u2len <= dstsize)
                        unicode_to_utf8(u2, (unsigned char *) dst + result_len);
 
                    result_len += u2len;
                }
                break;
            case CASEMAP_SPECIAL:
                /* replace with up to MAX_CASE_EXPANSION characters */
                Assert(simple == 0);
                for (int i = 0; i < MAX_CASE_EXPANSION && special[i]; i++)
                {
                    char32_t    u2 = special[i];
                    size_t      u2len = unicode_utf8len(u2);
 
                    if (result_len + u2len <= dstsize)
                        unicode_to_utf8(u2, (unsigned char *) dst + result_len);
 
                    result_len += u2len;
                }
                break;
        }
 
        srcoff += u1len;
    }
 
    if (result_len < dstsize)
        dst[result_len] = '\0';
 
    return result_len;
}
 
/*
 * Check that the condition matches Final_Sigma, described in Unicode Table
 * 3-17. The character at the given offset must be directly preceded by a
 * Cased character, and must not be directly followed by a Cased character.
 *
 * Case_Ignorable characters are ignored. NB: some characters may be both
 * Cased and Case_Ignorable, in which case they are ignored.
 */
static bool
check_final_sigma(const unsigned char *str, size_t len, size_t offset)
{
    /* the start of the string is not preceded by a Cased character */
    if (offset == 0)
        return false;
 
    /* iterate backwards, looking for Cased character */
    for (int i = offset - 1; i >= 0; i--)
    {
        if ((str[i] & 0x80) == 0 || (str[i] & 0xC0) == 0xC0)
        {
            char32_t    curr = utf8_to_unicode(str + i);
 
            if (pg_u_prop_case_ignorable(curr))
                continue;
            else if (pg_u_prop_cased(curr))
                break;
            else
                return false;
        }
        else if ((str[i] & 0xC0) == 0x80)
            continue;
 
        Assert(false);          /* invalid UTF-8 */
    }
 
    /* end of string is not followed by a Cased character */
    if (offset == len)
        return true;
 
    /* iterate forwards, looking for Cased character */
    for (int i = offset + 1; i < len && str[i] != '\0'; i++)
    {
        if ((str[i] & 0x80) == 0 || (str[i] & 0xC0) == 0xC0)
        {
            char32_t    curr = utf8_to_unicode(str + i);
 
            if (pg_u_prop_case_ignorable(curr))
                continue;
            else if (pg_u_prop_cased(curr))
                return false;
            else
                break;
        }
        else if ((str[i] & 0xC0) == 0x80)
            continue;
 
        Assert(false);          /* invalid UTF-8 */
    }
 
    return true;
}
 
/*
 * Unicode allows for special casing to be applied only under certain
 * circumstances. The only currently-supported condition is Final_Sigma.
 */
static bool
check_special_conditions(int conditions, const char *str, size_t len,
                         size_t offset)
{
    if (conditions == 0)
        return true;
    else if (conditions == PG_U_FINAL_SIGMA)
        return check_final_sigma((const unsigned char *) str, len, offset);
 
    /* no other conditions supported */
    Assert(false);
    return false;
}
 
/*
 * Map the given character to the requested case.
 *
 * If full is true, and a special case mapping is found and the conditions are
 * met, 'special' is set to the mapping result (which is an array of up to
 * MAX_CASE_EXPANSION characters) and CASEMAP_SPECIAL is returned.
 *
 * Otherwise, search for a simple mapping, and if found, set 'simple' to the
 * result and return CASEMAP_SIMPLE.
 *
 * If no mapping is found, return CASEMAP_SELF, and the caller should copy the
 * character without modification.
 */
static enum CaseMapResult
casemap(char32_t u1, CaseKind casekind, bool full,
        const char *src, size_t srclen, size_t srcoff,
        char32_t *simple, const char32_t **special)
{
    uint16      idx;
 
    /* Fast path for codepoints < 0x80 */
    if (u1 < 0x80)
    {
        /*
         * The first elements in all tables are reserved as 0 (as NULL). The
         * data starts at index 1, not 0.
         */
        *simple = casekind_map[casekind][u1 + 1];
 
        return CASEMAP_SIMPLE;
    }
 
    idx = case_index(u1);
 
    if (idx == 0)
        return CASEMAP_SELF;
 
    if (full && case_map_special[idx] &&
        check_special_conditions(special_case[case_map_special[idx]].conditions,
                                 src, srclen, srcoff))
    {
        *special = special_case[case_map_special[idx]].map[casekind];
        return CASEMAP_SPECIAL;
    }
 
    *simple = casekind_map[casekind][idx];
 
    return CASEMAP_SIMPLE;
}
 
/*
 * Find entry in simple case map.
 * If the entry does not exist, 0 will be returned.
 */
static char32_t
find_case_map(char32_t ucs, const char32_t *map)
{
    /* Fast path for codepoints < 0x80 */
    if (ucs < 0x80)
        /* The first elements in all tables are reserved as 0 (as NULL). */
        return map[ucs + 1];
    return map[case_index(ucs)];
}