Current File : //usr/include/mysql/server/private/cset_narrowing.h
/*
Copyright (c) 2023, MariaDB Corporation.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
#ifndef CSET_NARROWING_H_INCLUDED
#define CSET_NARROWING_H_INCLUDED
/*
A singleton class to provide "utf8mb3_from_mb4.charset()".
This is a variant of utf8mb3_general_ci that one can use when they have data
in MB4 and want to make index lookup keys in MB3.
*/
extern
class Charset_utf8narrow
{
struct my_charset_handler_st cset_handler;
struct charset_info_st cset;
public:
Charset_utf8narrow() :
cset_handler(*my_charset_utf8mb3_general_ci.cset),
cset(my_charset_utf8mb3_general_ci) /* Copy the CHARSET_INFO structure */
{
/* Insert our function wc_mb */
cset_handler.wc_mb= my_wc_mb_utf8mb4_bmp_only;
cset.cset=&cset_handler;
/* Charsets are compared by their name, so assign a different name */
LEX_CSTRING tmp= {STRING_WITH_LEN("utf8_mb4_to_mb3")};
cset.cs_name= tmp;
}
CHARSET_INFO *charset() { return &cset; }
} utf8mb3_from_mb4;
/*
A class to temporary change a field that uses utf8mb3_general_ci to enable
correct lookup key construction from string value in utf8mb4_general_ci
Intended usage:
// can do this in advance:
bool do_narrowing= Utf8_narrow::should_do_narrowing(field, value_cset);
...
// This sets the field to do narrowing if necessary:
Utf8_narrow narrow(field, do_narrowing);
// write to 'field' here
// item->save_in_field(field) or something else
// Stop doing narrowing
narrow.stop();
*/
class Utf8_narrow
{
Field *field;
DTCollation save_collation;
public:
static bool should_do_narrowing(const THD *thd, CHARSET_INFO *field_cset,
CHARSET_INFO *value_cset);
static bool should_do_narrowing(const Field *field, CHARSET_INFO *value_cset)
{
CHARSET_INFO *field_cset= field->charset();
THD *thd= field->table->in_use;
return should_do_narrowing(thd, field_cset, value_cset);
}
Utf8_narrow(Field *field_arg, bool is_applicable)
{
field= NULL;
if (is_applicable)
{
DTCollation mb3_from_mb4= utf8mb3_from_mb4.charset();
field= field_arg;
save_collation= field->dtcollation();
field->change_charset(mb3_from_mb4);
}
}
void stop()
{
if (field)
field->change_charset(save_collation);
#ifndef NDEBUG
field= NULL;
#endif
}
~Utf8_narrow()
{
DBUG_ASSERT(!field);
}
};
/*
@brief
Check if two fields can participate in a multiple equality using charset
narrowing.
@detail
Normally, check_simple_equality() checks this by calling:
left_field->eq_def(right_field)
This function does the same but takes into account we might use charset
narrowing:
- collations are not the same but rather an utf8mb{3,4}_general_ci pair
- for field lengths, should compare # characters, not #bytes.
*/
inline
bool fields_equal_using_narrowing(const THD *thd, const Field *left, const Field *right)
{
return
dynamic_cast<const Field_longstr*>(left) &&
dynamic_cast<const Field_longstr*>(right) &&
left->real_type() == right->real_type() &&
(Utf8_narrow::should_do_narrowing(left, right->charset()) ||
Utf8_narrow::should_do_narrowing(right, left->charset())) &&
left->char_length() == right->char_length();
};
#endif /* CSET_NARROWING_H_INCLUDED */
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