unicode_case.c

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/*-------------------------------------------------------------------------
 * unicode_case.c
 *      Unicode case mapping and case conversion.
 *
 * Portions Copyright (c) 2017-2024, 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 "mb/pg_wchar.h"
 
static const pg_case_map *find_case_map(pg_wchar ucs);
static size_t convert_case(char *dst, size_t dstsize, const char *src, ssize_t srclen,
                           CaseKind str_casekind, WordBoundaryNext wbnext,
                           void *wbstate);
 
pg_wchar
unicode_lowercase_simple(pg_wchar code)
{
    const pg_case_map *map = find_case_map(code);
 
    return map ? map->simplemap[CaseLower] : code;
}
 
pg_wchar
unicode_titlecase_simple(pg_wchar code)
{
    const pg_case_map *map = find_case_map(code);
 
    return map ? map->simplemap[CaseTitle] : code;
}
 
pg_wchar
unicode_uppercase_simple(pg_wchar code)
{
    const pg_case_map *map = find_case_map(code);
 
    return map ? map->simplemap[CaseUpper] : code;
}
 
/*
 * unicode_strlower()
 *
 * Convert src to lowercase, and return the result length (not including
 * terminating NUL).
 *
 * String src must be encoded in UTF-8. If srclen < 0, src must be
 * NUL-terminated.
 *
 * 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_strlower(char *dst, size_t dstsize, const char *src, ssize_t srclen)
{
    return convert_case(dst, dstsize, src, srclen, CaseLower, 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. If srclen < 0, src must be
 * NUL-terminated.
 *
 * 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.
 *
 * 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, ssize_t srclen,
                 WordBoundaryNext wbnext, void *wbstate)
{
    return convert_case(dst, dstsize, src, srclen, CaseTitle, 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. If srclen < 0, src must be
 * NUL-terminated.
 *
 * 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_strupper(char *dst, size_t dstsize, const char *src, ssize_t srclen)
{
    return convert_case(dst, dstsize, src, srclen, CaseUpper, NULL, NULL);
}
 
/*
 * 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
 * uppercase and other characters to lowercase.
 */
static size_t
convert_case(char *dst, size_t dstsize, const char *src, ssize_t srclen,
             CaseKind str_casekind, 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 ((srclen < 0 || srcoff < srclen) && src[srcoff] != '\0')
    {
        pg_wchar    u1 = utf8_to_unicode((unsigned char *) src + srcoff);
        int         u1len = unicode_utf8len(u1);
        const pg_case_map *casemap = find_case_map(u1);
 
        if (str_casekind == CaseTitle)
        {
            if (srcoff == boundary)
            {
                chr_casekind = CaseUpper;
                boundary = wbnext(wbstate);
            }
            else
                chr_casekind = CaseLower;
        }
 
        /* perform mapping, update result_len, and write to dst */
        if (casemap)
        {
            pg_wchar    u2 = casemap->simplemap[chr_casekind];
            pg_wchar    u2len = unicode_utf8len(u2);
 
            if (result_len + u2len <= dstsize)
                unicode_to_utf8(u2, (unsigned char *) dst + result_len);
 
            result_len += u2len;
        }
        else
        {
            /* no mapping; copy bytes from src */
            if (result_len + u1len <= dstsize)
                memcpy(dst + result_len, src + srcoff, u1len);
 
            result_len += u1len;
        }
 
        srcoff += u1len;
    }
 
    if (result_len < dstsize)
        dst[result_len] = '\0';
 
    return result_len;
}
 
/* find entry in simple case map, if any */
static const pg_case_map *
find_case_map(pg_wchar ucs)
{
    int         min;
    int         mid;
    int         max;
 
    /* all chars <= 0x80 are stored in array for fast lookup */
    Assert(lengthof(case_map) >= 0x80);
    if (ucs < 0x80)
    {
        const pg_case_map *map = &case_map[ucs];
 
        Assert(map->codepoint == ucs);
        return map;
    }
 
    /* otherwise, binary search */
    min = 0x80;
    max = lengthof(case_map) - 1;
    while (max >= min)
    {
        mid = (min + max) / 2;
        if (ucs > case_map[mid].codepoint)
            min = mid + 1;
        else if (ucs < case_map[mid].codepoint)
            max = mid - 1;
        else
            return &case_map[mid];
    }
 
    return NULL;
}