This document discusses character sets, encodings, and text conversion. It provides information on: - Character sets like Unicode, GB18030, Big5, and encodings like UTF-8, UTF-16, UTF-32. - Issues with encodings like Big5 that use characters with special meanings. - Projects like Chvar for mapping between traditional and simplified Chinese, and Khmerconv for converting Khmer fonts. - The bsdconv tool for decoding, encoding, and converting between character sets and encodings, including handling phases, fallback characters, cascading conversions, and look-through processing.

1. BSDCONV
Buganini Q
Since 2009

2. Charset & Encoding
Character Set
Collection of characters
Encoding
Binary representation

3. Charset & Encoding
..
Unicode (32bits addr. space)
.
Unicode up to U+10FFFF
.
Unicode BMP (up to U+FFFF)
.
(Basic Multilingual Plane)
. GB18030.
CNS11643
.
CP950
.
Latin1
Figure: Character Sets

4. Charset & Encoding
..
Unicode (32bits addr. space)
.
Unicode up to U+10FFFF
.
Unicode BMP (up to U+FFFF)
.GB18030.
CNS11643
.
CP950
.
Latin1
.
UTF-32 / UCS4
.
UTF-81 / UTF-16
.
UCS2
. GB18030.
CNS11643
.
CP950 (DBCS)
.
ISO-8859-1 / EBCDIC-0372
1
Could cover more but restricted by RFC 3629
2
Aka. IBM-37, some control characters are different from ISO-8859-1

5. Encoding :: UTF-32 / UCS4
Fixed Length
4 bytes
Filesize *= 4 for ASCII text file
Incompatible with C-style string convention
Endianness concern

6. Encoding :: UCS2
Fixed Length
2 bytes
Filesize *= 2 for ASCII text file
Incompatible with C-style string convention
Endianness concern
BMP-only

7. Encoding :: UTF-16
Variable Length
2 bytes / 4 bytes (Surrogate pairs)
Surrogates
Using U+D800..U+DFFF
Incompatible with C-style string convention
Endianness concern
******** ********
110110** ******** 110111** ********
Table: UTF-16 Structure

8. Encoding :: UTF-8
Variable Length
1~6 bytes
Compatible with C-style string convention
Self-synchronizing
Endian-neutral
Sorting order = Code point order
0******* (ASCII)
110***** 10******
1110**** 10****** 10******
11110*** 10****** 10****** 10******
111110** 10****** 10****** 10****** 10******
1111110* 10****** 10****** 10****** 10****** 10******
Table: UTF-8 Structure

9. Encoding :: CNS11643 (全字庫) #issue
http://www.cns11643.gov.tw/
Only used by Taiwan government
NOT a subset of Unicode
Not just an charset/encoding
Font
Pronunciation ㄇㄥ ˊ / méng
Radical 艸
Component 艹日月
Stroke
Tra/Sim mapping 萌蕄
Table: Examples for some information provided by 全字庫 for「萌」

10. Encoding :: CCCII
Variants
Variant glyph at different plane
Mostly used for library indexing
強 21 3D 48
彊 2D 3D 48
强 33 3D 48

11. Encoding :: Big5
Many incompatible variations (abusing PUA), none of
standard tools can rule them all
http://moztw.org/docs/big5/
Scenario Dominating encoding
Microsoft CP950
Taiwan BBS UAO (Unicode-at-Once)
gov.tw Big5-2003
gov.hk HKSCS (1999,2001,2004)
Special characters conflict
The second byte could be 0x5C (), 0x7C (|), 0x7E (~), which
may have special meaning in certain context

12. Bsdconv :: Decoding and Encoding
Alternative to iconv
... ISO-8859-1. :. UTF-8..
from
.
to
Figure: Basic two phases conversion

13. Bsdconv :: Codecs & Fallback
Optionally produce question mark (U+003F) as replacement
... UTF-8. ,. 3F. :. ASCII. ,. 3F..
from
.
to
Figure: Fallback codec
Transliteration
... UTF-8. :. CP936. ,. CP936-TRANS. ,. 3F..
from
.
to
Figure: Multiple fallback codecs

14. Encoding :: Big5
Many incompatible variations (abusing PUA), none of
standard tools can rule them all
http://moztw.org/docs/big5/
Scenario Dominating encoding
Microsoft CP950
Taiwan BBS UAO (Unicode-at-Once)
gov.tw Big5-2003
gov.hk HKSCS (1999,2001,2004)
Special characters conflict
The second byte could be 0x5C (), 0x7C (|), 0x7E (~), which
may have special meaning in certain context

15. Big5 5C issue (許功蓋)
BIG5:BIG5-5C,BIG5
# Input Output
Big5 Literal ” 成功” ” 成功 ”
ASCII/Hex ”xA6xA8xA5” ”xA6xA8xA5”
BIG5-5C,BIG5:BIG5
# Input Output
Big5 Literal ” 成功 ” ” 成功”
ASCII/Hex ”xA6xA8xA5” ”xA6xA8xA5”

16. Traditional/Simplified Chinese
NOT one-to-one mapping
Traditional 乾幹干
vs.
Simplified 干干干
Context dependent
之後、夜之后、入夜之後
Variants
峰、峯

17. Project Chvar (1/2)
https://github.com/buganini/chvar
..
..签簽. 籖籤.
Canonical group
.
Canonical group
.
Compatibility group
Figure: Two level grouping in Chvar
签 簽 籖 籤
TW 簽 - 籤 -
CN - 签 - 籖
CP950 簽 - 籤 -
GB2312 - 签 × ×
Table: Canonical Group
签 簽 籖 籤
TW 簽 - 簽 簽
CN - 签 签 签
CP950 簽 - 簽 簽
GB2312 - 签 签 签
Table: Compatibility Group

18. Project Chvar (2/2)
https://github.com/buganini/chvar
Normalization
Canonical Equivalence
Transliteration
Converted
or Canonical Equivalence
or Compatibility Equivalence
Fuzzy character matching
Compatibility Equivalence
签 簽 籖 籤
TW 簽 - 籤 -
CN - 签 - 籖
CP950 簽 - 籤 -
GB2312 - 签 × ×
Table: Canonical Group
签 簽 籖 籤
TW 簽 - 簽 簽
CN - 签 签 签
CP950 簽 - 簽 簽
GB2312 - 签 签 签
Table: Compatibility Group

19. Bsdconv :: Phases
Traditional Chinese ⇔ Simplified Chinese
... UTF-8. :. ZHTW. :. UTF-8..
from
.
inter
.
to
Figure: Conversion with inter-mapping phase

20. Bsdconv :: Phases
Furthermore, phrases mapping
... UTF-8. :. ZHTW. :. ZHTW-WORDS. :. UTF-8..
from
.
inter
.
inter
.
to
Figure: Conversion with multiple inter-mapping phases

21. Unicode :: Casing
IS complicated
Lowercase Uppercase
a A
i I
Table: English
Lowercase Uppercase
ı I
i İ
Table: Turkic
Lowercase Uppercase
a A
à A
Table: French
Lowercase Uppercase
σ Σ
ς Σ
Table: Greek
Default Case Folding

22. Unicode :: Normalization Forms (1/2)
UAX#15
Indexing
Identification security
Username, Domain name
Combining sequence Ç C + ◌̧
Ordering of combining marks q+◌̇+◌̣ q+◌̣+◌̇
Hangul 가 ᄀ + ᅡ
Singleton Ω Ω
Table: Canonical Equivalence

23. Unicode :: Normalization Forms (2/2)
UAX#15
Font variants ℌ H
Breaking differences NBSP SP
Cursive forms ‫ﻧ‬ ‫ﻨ‬
Circled ① 1
Width, size, rotated
ｶ カ
︷ {
Superscripts/subscripts ⁹ 9
Squared characters ㍿ 株 + 式 + 会 + 社
Fractions ¾ 3 + / + 4
Others dž d + z + ◌̌
Table: Compatibility Equivalence

24. Normalization for fuzzy matching
UTF-8:UPPER:UTF-8
Input: aăⅷDžбⓐᾥ
Output: AĂⅧDŽБⒶᾭ
UTF-8:ZH-FUZZY-TW:KANA-PHONETIC:NFKD-
CASEFOLD:UTF-8
Input: ¼ℌℍăDžⓐ⁹ 灣湾ド鬒鬒㊣ æß
Output: 1⁄4hhădža9 灣灣 do 鬒鬒正 æss
Composition Decomposition
Canonical NFC NFD
Compatibility NFKC NFKD
Table: The four Unicode normalization forms and the transformations

25. Bsdconv :: Cascade
Re-encode
... UTF-8. :. ISO-8859-1. |. BIG5. :. UTF-8..
from
.
to
.
from
.
to
Figure: Cascaded conversions
Input Output
¥x¥_ 台北

26. Bsdconv :: Codec argument
Other than question mark
... UTF-8. ,. ANY#0121. :. ASCII. ,. ANY#21..
from
.
to
Figure: Codec argument
Or more than one character
... UTF-8. ,. ANY#013F.0121. :. ASCII. ,. ANY#21..
from
.
to
Figure: Data list, separated by dot

27. Bsdconv :: Alias
from/3F
ANY#013F&ERROR
to/3F
ANY#3F&ERROR
from/UTF-8
ASCII,_UTF-8
inter/NFKD
_NFKD:_NF-HANGUL-DECOMPOSITION:_NF-ORDER
inter/NFKC
NFKD:_NFC:_NF-HANGUL-COMPOSITION
inter/NFKD-CASEFOLD
NFD:CASEFOLD:NFKD:CASEFOLD:NFKD
filter/01
UNICODE

28. Charset & Encoding
..
Unicode (32bits addr. space)
.
Unicode up to U+10FFFF
.
Unicode BMP (up to U+FFFF)
.
(Basic Multilingual Plane)
. GB18030.
CNS11643
.
CP950
.
Latin1
Figure: Character Sets

29. Bsdconv :: Types
(01) Unicode
(02) CNS11643
(03) Byte
(04) Chinese components
(1B) ANSI control sequences
(00) Bsdconv special characters

30. Encoding :: CNS11643 (全字庫) #issue
http://www.cns11643.gov.tw/
Only used by Taiwan government
NOT a subset of Unicode
Not just an charset/encoding
Font
Pronunciation ㄇㄥ ˊ / méng
Radical 艸
Component 艹日月
Stroke
Tra/Sim mapping 萌蕄
Table: Examples for some information provided by 全字庫 for「萌」

31. Chinese components composition
https://github.com/buganini/chicomp
UTF-8:ZH-DECOMP:ZH-COMP:UTF-8
Input: 功夫不好不要艹我
Output: 巭孬嫑莪
UTF-8:ZH-DECOMP:ZH-COMP:CHEWING:UTF-8
Input: 功夫不好不要艹我
Output: ㄆㄨ ㄋㄠ ㄧㄠ ㄜ ˊ
UTF-8:ZH-DECOMP:ZH-COMP:CHEWING:HAN-
PINYIN:UTF-8
Input: 功夫不好不要艹我
Output: pu nao yao [uh]2

32. Bsdconv :: Flags
FREE - memory management
MARK - identifier

33. Bsdconv :: Cascade
Re-encode
... UTF-8. :. ISO-8859-1. |. BIG5. :. UTF-8..
from
.
to
.
from
.
to
Figure: Cascaded conversions
Input Output
¥x¥_ 台北

34. Look-through (1/4)
..%u03B1%CE%B2.
Input (UTF-8 literal)
. ESCAPE : ....
Decoder
.
..
01
.
03
.
B1
.
03
.
CE
.
03
.
B2
.
Internal data
.
Entity Unicode UTF-8 Hex
α U+03B1 CEB1
β U+03B2 CEB2
Figure: ESCAPE:PASS#MARK&FOR=1,BYTE|PASS#UNMARK,UTF-8:UTF-8

35. Look-through (2/4)
..
..01.
03
.
B1
. 03.
CE
. 03.
B2.
Internal data
. ... : PASS#MARK&FOR=1,BYTE.
Encoder
.
..
01
.
03
.
B1
.
MARK
.
CE
.
B2
.
Internal data
.
Entity Unicode UTF-8 Hex
α U+03B1 CEB1
β U+03B2 CEB2
Figure: ESCAPE:PASS#MARK&FOR=1,BYTE|PASS#UNMARK,UTF-8:UTF-8

36. Look-through (3/4)
..
..01.
03
.
B1
.
MARK
. CE. B2
.
Internal data
. PASS#UNMARK,UTF-8 : ....
Decoder
.
..
01
.
03
.
B1
.
01
.
03
.
B2
.
Internal data
.
Entity Unicode UTF-8 Hex
α U+03B1 CEB1
β U+03B2 CEB2
Figure: ESCAPE:PASS#MARK&FOR=1,BYTE|PASS#UNMARK,UTF-8:UTF-8

37. Look-through (4/4)
..
01
.
03
.
B1
.
01
.
03
.
B2
Internal data
... : UTF-8
Encoder
..
CE
.
B1
.”α”.
CE
.
B2
. ”β”
Internal data
αβ
Output (UTF-8 literal)
Entity Unicode UTF-8 Hex
α U+03B1 CEB1
β U+03B2 CEB2
Figure: ESCAPE:PASS#MARK&FOR=1,BYTE|PASS#UNMARK,UTF-8:UTF-8

38. Unicode :: East Asian Width (1/2)
UAX#11
..
..Narrow.
Halfwidth
..
.. Wide.
Fullwidth
.
Ambiguous
.
Neutral
Figure: Venn Diagram Showing the Set Relations for Six Categories

39. Unicode :: East Asian Width (2/2)
UAX#11
Narrow Ambiguous Wide
Я
N ऊ
Na A Ａ F
H ｶ カ W
咦 W
Table: Examples for Each Character Class and Their Resolved Widths
Na Narrow
N Neural, usually treated as Narrow
W Wide
F Fullwidth
H Halfwidth
Table: Width attributes

40. String width measurement
echo "42(ˊ_>ˋ) 紅茶" | bsdconv UTF-8:WIDTH:NULL
FULL: 2
HALF: 7
AMBI: 2

41. Chinese charset encoding detection
https://github.com/buganini/chiconv
ENCODING:SCORE#WITH=CJK:COUNT:ZH-
BONUS:ZHTW:ZH-BONUS-PHRASE:NULL
Score(s) = $SCORE−$IERR∗$COUNT∗0.01
$COUNT
帥呆了 ⇒ UTF-8:SCORE#WITH=CJK:……
ENCODING SCORE COUNT IERR Score(s)
UTF-8 19 4 0 4.75
BIG5 8 3 2 -4.0
GBK 4 1 4 -36.0
CCCII 36 9 0 4.0
UTF-16LE 20 5 2 0.0

42. Khmer legacy font converter
https://github.com/buganini/khmerconv
Issues
Encoding without registerd name, bound on fonts
Stored in CP1252 or UTF-8
Solution
Two pass detection
Detect encoding
Detect font family (currently not working)
(High converage in SBCS)
Algorithm ported from Khmer Converter3
Khmer Converter
Mapping
Reordering
Visual order vs. Unicode model
Unicode Model: baseCharacter [+ [Robat/Shifter] + [Coeng*]
+ [Shifter] + [Vowel] + [Sign]]
3
http://www.khmeros.info/en/khmer-converter

43. Encoding :: Big5
Many incompatible variations (abusing PUA), none of
standard tools can rule them all
http://moztw.org/docs/big5/
Scenario Dominating encoding
Microsoft CP950
Taiwan BBS UAO (Unicode-at-Once)
gov.tw Big5-2003
gov.hk HKSCS (1999,2001,2004)
Special characters conflict
The second byte could be 0x5C (), 0x7C (|), 0x7E (~), which
may have special meaning in certain context

44. Unicode :: East Asian Width (1/2)
UAX#11
..
..Narrow.
Halfwidth
..
.. Wide.
Fullwidth
.
Ambiguous
.
Neutral
Figure: Venn Diagram Showing the Set Relations for Six Categories

45. Unicode :: East Asian Width (2/2)
UAX#11
Narrow Ambiguous Wide
Я
N ऊ
Na A Ａ F
H ｶ カ W
咦 W
Table: Examples for Each Character Class and Their Resolved Widths
Na Narrow
N Neural, usually treated as Narrow
W Wide
F Fullwidth
H Halfwidth
Table: Width attributes

46. Terminal transcoding
https://github.com/buganini/bug5
Issues
UAO: Non-standard big5 extension
Double color hack
ANSI control sequence in the middle of DBCS
Ambiguous width characters
luit/screen cannot help
Solution (tl;dr)
Big5 to Unicode
ANSI-CONTROL,BYTE:BIG5-DEFRAG:
BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:
UTF-8,PASS#FOR=1B
Unicode to Big5
UTF-8,00,BYTE:ZHTW:AMBIGUOUS-UNPAD:
BIG5,CP950-TRANS,UAO,00,ANY#3F

47. Bug5 explained (1/6)
..⋆xC5x1B[1mxE5.
Input (Big5 literal)
. ANSI-CONTROL,BYTE : ....
Decoder
.
..
03
.
A1
.
03
.
B9
.
03
.
C5
.
1B
.
5B
.
31
.
6D
.
03
.
E5
.
Internal data
.
Entity Unicode UTF-8 Hex Big5 Hex
⋆ U+2605 E29885 A1B9
驚 U+9A5A E9A99A C5E5
[ U+005B 5B 5B
1 U+0031 31 31
m U+006D 6D 6D
(NBSP) U+00A0 C2A0 -
Figure: ANSI-CONTROL,BYTE:BIG5-DEFRAG:BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:UTF-8,PASS#FOR=1B

48. Bug5 explained (2/6)
..
..03.
A1
. 03.
B9
. 03.
C5
. 1B.
5B
.
31
.
6D
. 03.
E5.
Internal data
. ... : BIG5-DEFRAG : ....
Inter-conversion
.
..
03
.
A1
.
03
.
B9
.
03
.
C5
.
03
.
E5
.
1B
.
5B
.
31
.
6D
.
Internal data
.
Entity Unicode UTF-8 Hex Big5 Hex
⋆ U+2605 E29885 A1B9
驚 U+9A5A E9A99A C5E5
[ U+005B 5B 5B
1 U+0031 31 31
m U+006D 6D 6D
(NBSP) U+00A0 C2A0 -
Figure: ANSI-CONTROL,BYTE:BIG5-DEFRAG:BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:UTF-8,PASS#FOR=1B

49. Bug5 explained (3/6)
..
..03.
A1
. 03.
B9
. 03.
C5
. 03.
E5
. 1B.
5B
.
31
.
6D
.
Internal data
. ... : BYTE,PASS#MARK&FOR=1B.
Encoder
.
..
A1
.
B9
.
C5
.
E5
.
1B
.
5B
.
31
.
6D
.
MARK
.
Internal data
.
Entity Unicode UTF-8 Hex Big5 Hex
⋆ U+2605 E29885 A1B9
驚 U+9A5A E9A99A C5E5
[ U+005B 5B 5B
1 U+0031 31 31
m U+006D 6D 6D
(NBSP) U+00A0 C2A0 -
Figure: ANSI-CONTROL,BYTE:BIG5-DEFRAG:BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:UTF-8,PASS#FOR=1B

50. Bug5 explained (4/6)
..
..A1. B9. C5. E5. 1B.
5B
.
31
.
6D
.
MARK
.
Internal data
. PASS#UNMARK,BIG5 : ....
Decoder
.
..
01
.
26
.
05
.
01
.
9A
.
5A
.
1B
.
5B
.
31
.
6D
.
Internal data
.
Entity Unicode UTF-8 Hex Big5 Hex
⋆ U+2605 E29885 A1B9
驚 U+9A5A E9A99A C5E5
[ U+005B 5B 5B
1 U+0031 31 31
m U+006D 6D 6D
(NBSP) U+00A0 C2A0 -
Figure: ANSI-CONTROL,BYTE:BIG5-DEFRAG:BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:UTF-8,PASS#FOR=1B

51. Bug5 explained (5/6)
..
..01.
26
.
05
. 01.
9A
.
5A
. 1B.
5B
.
31
.
6D
.
Internal data
. ... : AMBIGUOUS-PAD : ....
Inter-conversion
.
..
01
.
26
.
05
.
01
.
A0
.
01
.
9A
.
5A
.
1B
.
5B
.
31
.
6D
.
Internal data
.
Entity Unicode UTF-8 Hex Big5 Hex
⋆ U+2605 E29885 A1B9
驚 U+9A5A E9A99A C5E5
[ U+005B 5B 5B
1 U+0031 31 31
m U+006D 6D 6D
(NBSP) U+00A0 C2A0 -
Figure: ANSI-CONTROL,BYTE:BIG5-DEFRAG:BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:UTF-8,PASS#FOR=1B

52. Bug5 explained (6/6)
..
..01.
26
.
05
. 01.
A0
. 01.
9A
.
5A
. 1B.
5B
.
31
.
6D
.
Internal data
. ... : UTF-8,PASS#FOR=1B.
Encoder
.
⋆ 驚 x1B[1m
.
Output (UTF-8 literal)
.
Entity Unicode UTF-8 Hex Big5 Hex
⋆ U+2605 E29885 A1B9
驚 U+9A5A E9A99A C5E5
[ U+005B 5B 5B
1 U+0031 31 31
m U+006D 6D 6D
(NBSP) U+00A0 C2A0 -
Figure: ANSI-CONTROL,BYTE:BIG5-DEFRAG:BYTE,PASS#MARK&FOR=1B|
PASS#UNMARK,BIG5:AMBIGUOUS-PAD:UTF-8,PASS#FOR=1B

53. Bsdconv :: Bindings
Python/Ruby/Go/Perl/PHP
https://pypi.python.org/pypi/bsdconv
https://rubygems.org/gems/ruby-bsdconv
https://github.com/buganini/go-bsdconv
https://github.com/buganini/perl-bsdconv
https://github.com/buganini/php-bsdconv
PostgreSQL/MySQL
https://github.com/buganini/postgres-bsdconv
https://github.com/buganini/mysql-udf-bsdconv
Irssi
https://github.com/buganini/irssi-scripts/blob/master/irssi-bsdconv.pl

54. Bsdconv :: GUI
https://github.com/buganini/gbsdconv
Alternative to ConvertZ
Text
File name
File content
Meta tag

55. Thanks
ESCAPE,UTF-8:PA
SS#FOR=UNICODE&M
ARK,BYTE|PASS#UNMA
RK,UTF-8:NFC:ASCII,ES
CAPE|
https://github.com/buganini/bsdconv