mirror of
https://github.com/MariaDB/server.git
synced 2025-11-03 20:36:16 +01:00
281 lines
9.2 KiB
Text
281 lines
9.2 KiB
Text
|
|
CHARSET_INFO
|
|
============
|
|
A structure containing data for charset+collation pair implementation.
|
|
|
|
Virtual functions that use this data are collected into separate
|
|
structures, MY_CHARSET_HANDLER and MY_COLLATION_HANDLER.
|
|
|
|
|
|
typedef struct charset_info_st
|
|
{
|
|
uint number;
|
|
uint primary_number;
|
|
uint binary_number;
|
|
uint state;
|
|
|
|
const char *csname;
|
|
const char *name;
|
|
const char *comment;
|
|
|
|
uchar *ctype;
|
|
uchar *to_lower;
|
|
uchar *to_upper;
|
|
uchar *sort_order;
|
|
|
|
uint16 *tab_to_uni;
|
|
MY_UNI_IDX *tab_from_uni;
|
|
|
|
uchar state_map[256];
|
|
uchar ident_map[256];
|
|
|
|
uint strxfrm_multiply;
|
|
uint mbminlen;
|
|
uint mbmaxlen;
|
|
uint16 max_sort_char; /* For LIKE optimization */
|
|
|
|
MY_CHARSET_HANDLER *cset;
|
|
MY_COLLATION_HANDLER *coll;
|
|
|
|
} CHARSET_INFO;
|
|
|
|
|
|
CHARSET_INFO fields description:
|
|
===============================
|
|
|
|
|
|
Numbers (identifiers)
|
|
---------------------
|
|
|
|
number - an ID uniquely identifying this charset+collation pair.
|
|
|
|
primary_number - ID of a charset+collation pair, which consists
|
|
of the same character set and the default collation of this
|
|
character set. Not really used now. Intended to optimize some
|
|
parts of the code where we need to find the default collation
|
|
using its non-default counterpart for the given character set.
|
|
|
|
binary_number - ID of a charset+collation pair, which consists
|
|
of the same character set and the binary collation of this
|
|
character set. Not really used now.
|
|
|
|
Names
|
|
-----
|
|
|
|
csname - name of the character set for this charset+collation pair.
|
|
name - name of the collation for this charset+collation pair.
|
|
comment - a text comment, displayed in "Description" column of
|
|
SHOW CHARACTER SET output.
|
|
|
|
Conversion tables
|
|
-----------------
|
|
|
|
ctype - pointer to array[257] of "type of characters"
|
|
bit mask for each character, e.g., whether a
|
|
character is a digit, letter, separator, etc.
|
|
|
|
Monty 2004-10-21:
|
|
If you look at the macros, we use ctype[(char)+1].
|
|
ctype[0] is traditionally in most ctype libraries
|
|
reserved for EOF (-1). The idea is that you can use
|
|
the result from fgetc() directly with ctype[]. As
|
|
we have to be compatible with external ctype[] versions,
|
|
it's better to do it the same way as they do...
|
|
|
|
to_lower - pointer to array[256] used in LCASE()
|
|
to_upper - pointer to array[256] used in UCASE()
|
|
sort_order - pointer to array[256] used for strings comparison
|
|
|
|
In all Asian charsets these arrays are set up as follows:
|
|
|
|
- All bytes in the range 0x80..0xFF were marked as letters in the
|
|
ctype array.
|
|
|
|
- The to_lower and to_upper arrays map only ASCII letters.
|
|
UPPER() and LOWER() doesn't really work for multi-byte characters.
|
|
Most of the characters in Asian character sets are ideograms
|
|
anyway and they don't have case mapping. However, there are
|
|
still some characters from European alphabets.
|
|
For example:
|
|
_ujis 0x8FAAF2 - LATIN CAPITAL LETTER Y WITH ACUTE
|
|
_ujis 0x8FABF2 - LATIN SMALL LETTER Y WITH ACUTE
|
|
|
|
But they don't map to each other with UPPER and LOWER operations.
|
|
|
|
- The sort_order array is filled case insensitively for the
|
|
ASCII range 0x00..0x7F, and in "binary" fashion for the multi-byte
|
|
range 0x80..0xFF for these collations:
|
|
|
|
cp932_japanese_ci,
|
|
euckr_korean_ci,
|
|
eucjpms_japanese_ci,
|
|
gb2312_chinese_ci,
|
|
sjis_japanese_ci,
|
|
ujis_japanese_ci.
|
|
|
|
So multi-byte characters are sorted just according to their codes.
|
|
|
|
|
|
- Two collations are still case insensitive for the ASCII characters,
|
|
but have special sorting order for multi-byte characters
|
|
(something more complex than just according to codes):
|
|
|
|
big5_chinese_ci
|
|
gbk_chinese_ci
|
|
|
|
So handlers for these collations use only the 0x00..0x7F part
|
|
of their sort_order arrays, and apply the special functions
|
|
for multi-byte characters
|
|
|
|
In Unicode character sets we have full support of UPPER/LOWER mapping,
|
|
for sorting order, and for character type detection.
|
|
"utf8mb3_general_ci" still has the "old-fashioned" arrays
|
|
like to_upper, to_lower, sort_order and ctype, but they are
|
|
not really used (maybe only in some rare legacy functions).
|
|
|
|
|
|
|
|
Unicode conversion data
|
|
-----------------------
|
|
For 8-bit character sets:
|
|
|
|
tab_to_uni : array[256] of charset->Unicode translation
|
|
tab_from_uni: a structure for Unicode->charset translation
|
|
|
|
Non-8-bit charsets have their own structures per charset
|
|
hidden in corresponding ctype-xxx.c file and don't use
|
|
tab_to_uni and tab_from_uni tables.
|
|
|
|
|
|
Parser maps
|
|
-----------
|
|
state_map[]
|
|
ident_map[]
|
|
|
|
These maps are used to quickly identify whether a character is an
|
|
identifier part, a digit, a special character, or a part of another
|
|
SQL language lexical item.
|
|
|
|
Probably can be combined with ctype array in the future.
|
|
But for some reasons these two arrays are used in the parser,
|
|
while a separate ctype[] array is used in the other part of the
|
|
code, like fulltext, etc.
|
|
|
|
|
|
Miscellaneous fields
|
|
--------------------
|
|
|
|
strxfrm_multiply - how many times a sort key (that is, a string
|
|
that can be passed into memcmp() for comparison)
|
|
can be longer than the original string.
|
|
Usually it is 1. For some complex
|
|
collations it can be bigger. For example,
|
|
in latin1_german2_ci, a sort key is up to
|
|
two times longer than the original string.
|
|
e.g. Letter 'A' with two dots above is
|
|
substituted with 'AE'.
|
|
mbminlen - minimum multi-byte sequence length.
|
|
Now always 1 except for ucs2. For ucs2,
|
|
it is 2.
|
|
mbmaxlen - maximum multi-byte sequence length.
|
|
1 for 8-bit charsets. Can be also 2 or 3.
|
|
|
|
max_sort_char - for LIKE range
|
|
in case of 8-bit character sets - native code
|
|
of maximum character (max_str pad byte);
|
|
in case of UTF8 and UCS2 - Unicode code of the maximum
|
|
possible character (usually U+FFFF). This code is
|
|
converted to multi-byte representation (usually 0xEFBFBF)
|
|
and then used as a pad sequence for max_str.
|
|
in case of other multi-byte character sets -
|
|
max_str pad byte (usually 0xFF).
|
|
|
|
MY_CHARSET_HANDLER
|
|
==================
|
|
|
|
MY_CHARSET_HANDLER is a collection of character-set
|
|
related routines. Defined in m_ctype.h. Have the
|
|
following set of functions:
|
|
|
|
Multi-byte routines
|
|
------------------
|
|
ismbchar() - detects whether the given string is a multi-byte sequence
|
|
mbcharlen() - returns length of multi-byte sequence starting with
|
|
the given character
|
|
numchars() - returns number of characters in the given string, e.g.
|
|
in SQL function CHAR_LENGTH().
|
|
charpos() - calculates the offset of the given position in the string.
|
|
Used in SQL functions LEFT(), RIGHT(), SUBSTRING(),
|
|
INSERT()
|
|
|
|
well_formed_len()
|
|
- returns length of a given multi-byte string in bytes
|
|
Used in INSERTs to shorten the given string so it
|
|
a) is "well formed" according to the given character set
|
|
b) can fit into the given data type
|
|
|
|
lengthsp() - returns the length of the given string without trailing spaces.
|
|
|
|
|
|
Unicode conversion routines
|
|
---------------------------
|
|
mb_wc - converts the left multi-byte sequence into its Unicode code.
|
|
mc_mb - converts the given Unicode code into multi-byte sequence.
|
|
|
|
|
|
Case and sort conversion
|
|
------------------------
|
|
caseup_str - converts the given 0-terminated string to uppercase
|
|
casedn_str - converts the given 0-terminated string to lowercase
|
|
caseup - converts the given string to lowercase using length
|
|
casedn - converts the given string to lowercase using length
|
|
|
|
Number-to-string conversion routines
|
|
------------------------------------
|
|
snprintf()
|
|
long10_to_str()
|
|
longlong10_to_str()
|
|
|
|
The names are pretty self-describing.
|
|
|
|
String padding routines
|
|
-----------------------
|
|
fill() - writes the given Unicode value into the given string
|
|
with the given length. Used to pad the string, usually
|
|
with space character, according to the given charset.
|
|
|
|
String-to-number conversion routines
|
|
------------------------------------
|
|
strntol()
|
|
strntoul()
|
|
strntoll()
|
|
strntoull()
|
|
strntod()
|
|
|
|
These functions are almost the same as their STDLIB counterparts,
|
|
but also:
|
|
- accept length instead of 0-terminator
|
|
- are character set dependent
|
|
|
|
Simple scanner routines
|
|
-----------------------
|
|
scan() - to skip leading spaces in the given string.
|
|
Used when a string value is inserted into a numeric field.
|
|
|
|
|
|
|
|
MY_COLLATION_HANDLER
|
|
====================
|
|
strnncoll() - compares two strings according to the given collation
|
|
strnncollsp() - like the above but ignores trailing spaces
|
|
strnxfrm() - makes a sort key suitable for memcmp() corresponding
|
|
to the given string
|
|
like_range() - creates a LIKE range, for optimizer
|
|
wildcmp() - wildcard comparison, for LIKE
|
|
strcasecmp() - 0-terminated string comparison
|
|
instr() - finds the first substring appearance in the string
|
|
hash_sort() - calculates hash value taking into account
|
|
the collation rules, e.g. case-insensitivity,
|
|
accent sensitivity, etc.
|
|
|
|
|