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Obsolete multibyte encoding for Unicode

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UTF-1
MIME / IANA	ISO-10646-UTF-1
Language	International
Current status	Obscure, of mainly historical interest.
Classification	Unicode Transformation Format,extended ASCII,variable-width encoding
Extends	US-ASCII
Transforms / Encodes	ISO/IEC 10646 (Unicode)
Succeeded by	UTF-8

UTF-1 is an obsolete method of transformingISO/IEC 10646/Unicode into a stream ofbytes. Its design does not provideself-synchronization, which makes searching forsubstrings and error recovery difficult. It reuses the ASCII printing characters for multi-byte encodings, making it unsuited for some uses (for instance Unix filenames cannot contain the byte value used for forward slash). UTF-1 is also slow to encode or decode due to its use of division and multiplication by a number which is not a power of 2. Due to these issues, it did not gain acceptance and was quickly replaced byUTF-8.

Design

[edit]

Similar toUTF-8, UTF-1 is avariable-width encoding that is backwards-compatible withASCII. EveryUnicode code point is represented by either a single byte, or a sequence of two, three, orfive bytes. All ASCII code points are a single byte (the code pointsU+0080 throughU+009F are also single bytes).

UTF-1 does not use theC0 and C1 control codes or the space character in multi-byte encodings: a byte in the range 0–0x20 or 0x7F–0x9F always stands for the corresponding code point. This design with 66protected characters tried to beISO/IEC 2022 compatible.

UTF-1 uses "modulo 190" arithmetic (256 − 66 = 190). For comparison, UTF-8 protects all 128 ASCII characters and needs one bit for this, and a second bit to make it self-synchronizing, resulting in "modulo 64" arithmetic (8 − 2 = 6;2⁶ = 64).BOCU-1 protects only the minimal set required forMIME-compatibility (0x00, 0x07–0x0F, 0x1A–0x1B, and 0x20), resulting in "modulo 243" arithmetic (256 − 13 = 243).

UTF-1
First code point	Last code point	Byte 1	Byte 2	Byte 3	Byte 4	Byte 5
U+0000	U+009F	00–9F
U+00A0	U+00FF	A0	A0–FF
U+0100	U+4015	A1–F5	21–7E, A0–FF
U+4016	U+38E2D	F6–FB	21–7E, A0–FF	21–7E, A0–FF
U+38E2E	U+7FFFFFFF	FC–FF	21–7E, A0–FF	21–7E, A0–FF	21–7E, A0–FF	21–7E, A0–FF

code point	UTF-8	UTF-1
U+007F	7F	7F
U+0080	C2 80	80
U+009F	C2 9F	9F
U+00A0	C2 A0	A0 A0
U+00BF	C2 BF	A0 BF
U+00C0	C3 80	A0 C0
U+00FF	C3 BF	A0 FF
U+0100	C4 80	A1 21
U+015D	C5 9D	A1 7E
U+015E	C5 9E	A1 A0
U+01BD	C6 BD	A1 FF
U+01BE	C6 BE	A2 21
U+07FF	DF BF	AA 72
U+0800	E0 A0 80	AA 73
U+0FFF	E0 BF BF	B5 48
U+1000	E1 80 80	B5 49
U+4015	E4 80 95	F5 FF
U+4016	E4 80 96	F6 21 21
U+D7FF	ED 9F BF	F7 2F C3
U+E000	EE 80 80	F7 3A 79
U+F8FF	EF A3 BF	F7 5C 3C
U+FDD0	EF B7 90	F7 62 BA
U+FDEF	EF B7 AF	F7 62 D9
U+FEFF	EF BB BF	F7 64 4C
U+FFFD	EF BF BD	F7 65 AD
U+FFFE	EF BF BE	F7 65 AE
U+FFFF	EF BF BF	F7 65 AF
U+10000	F0 90 80 80	F7 65 B0
U+38E2D	F0 B8 B8 AD	FB FF FF
U+38E2E	F0 B8 B8 AE	FC 21 21 21 21
U+FFFFF	F3 BF BF BF	FC 21 37 B2 7A
U+100000	F4 80 80 80	FC 21 37 B2 7B
U+10FFFF	F4 8F BF BF	FC 21 39 6E 6C
U+7FFFFFFF	FD BF BF BF BF BF	FD BD 2B B9 40

Although modern Unicode ends at U+10FFFF, both UTF-1 and UTF-8 were designed to encode the complete 31 bits of the originalUniversal Character Set (UCS-4), and the last entry in this table shows this original final code point.

References

[edit]

"The Unicode Standard: Appendix F FSS-UTF"(PDF) (PDF, 768 KiB). Version 1.1. Unicode, Inc.
ISO/IEC JTC 1/SC2/WG2 (1993-01-21)."ISO IR 178: UCS Transformation Format One (UTF-1)"(PDF) (PDF, 256 KiB) (1 ed.). Registration number 178. Archived fromthe original(PDF) on 2015-03-18.{{cite web}}: CS1 maint: numeric names: authors list (link)
Czyborra, Roman (1998-11-30)."Unicode Transformation Formats: UTF-8 & Co".Archived from the original on 2016-06-07. Retrieved2016-06-07.
Yergeau, F. (November 2003).UTF-8, a transformation format of ISO 10646.IETF.doi:10.17487/RFC3629. STD 63. RFC 3629.

Unicode

Code points

Characters

Special purpose	BOM Combining grapheme joiner Left-to-right mark /Right-to-left mark Soft hyphen Variant form Word joiner Zero-width joiner Zero-width non-joiner Zero-width space
Lists	Characters CJK Unified Ideographs Combining character Duplicate characters Numerals Scripts Spaces Symbols Halfwidth and fullwidth Alias names and abbreviations Whitespace characters

Processing

Algorithms	Bidirectional text Collation ISO/IEC 14651 Equivalence Variation sequences International Ideographs Core
Comparison of encodings	BOCU-1 CESU-8 Punycode SCSU UTF-1 UTF-7 UTF-8 UTF-16/UCS-2 UTF-32/UCS-4 UTF-EBCDIC

On pairs of
code points

Usage

Related standards

Related topics

Scripts and symbols in Unicode
Common and inherited scripts	Combining marks Diacritics Punctuation marks Spaces Numbers
Modern scripts	Adlam Arabic Armenian Balinese Bamum Batak Bengali Beria Erfe Bopomofo Braille Buhid Burmese Canadian Aboriginal Chakma Cham Cherokee CJK Unified Ideographs (Han) Cyrillic Deseret Devanagari Garay Geʽez Georgian Greek Gujarati Gunjala Gondi Gurmukhi Gurung Khema Hangul Hanifi Rohingya Hanja Hanunuoo Hebrew Hiragana Javanese Kanji Kannada Katakana Kayah Li Khmer Kirat Rai Lao Latin Lepcha Limbu Lisu (Fraser) Lontara Malayalam Masaram Gondi Mende Kikakui Medefaidrin Miao (Pollard) Mongolian Mru N'Ko Nag Mundari New Tai Lue Nüshu Nyiakeng Puachue Hmong Odia Ol Chiki Ol Onal Osage Osmanya Pahawh Hmong Pau Cin Hau Pracalit (Newa) Ranjana Rejang Samaritan Saurashtra Shavian Sinhala Sorang Sompeng Sundanese Sunuwar Syriac Tagbanwa Tai Le Tai Tham Tai Viet Tai Yo Tamil Tangsa Telugu Thaana Thai Tibetan Tifinagh Tirhuta Tolong Siki Toto Vai Wancho Warang Citi Yi
Ancient and historic scripts	Ahom Anatolian hieroglyphs Ancient North Arabian Avestan Bassa Vah Bhaiksuki Brāhmī Carian Caucasian Albanian Coptic Cuneiform Cypriot Cypro-Minoan Dives Akuru Dogra Egyptian hieroglyphs Elbasan Elymaic Glagolitic Gothic Grantha Hatran Imperial Aramaic Inscriptional Pahlavi Inscriptional Parthian Kaithi Kawi Kharosthi Khitan small script Khojki Khudawadi Khwarezmian (Chorasmian) Linear A Linear B Lycian Lydian Mahajani Makasar Mandaic Manichaean Marchen Meetei Mayek Meroitic Modi Multani Nabataean Nandinagari Ogham Old Hungarian Old Italic Old Permic Old Persian cuneiform Old Sogdian Old Turkic Old Uyghur Palmyrene ʼPhags-pa Phoenician Psalter Pahlavi Runic Sharada Siddham Sidetic Sogdian South Arabian Soyombo Sylheti Nagri Tagalog (Baybayin) Takri Tangut Todhri Tulu Tigalari Ugaritic Vithkuqi Yezidi Zanabazar Square
Notational scripts	Duployan SignWriting
Symbols, emojis	Cultural, political, and religious symbols Currency Control Pictures Mathematical operators and symbols Glossary Phonetic symbols (including IPA) Emoji
Category: Unicode Category: Unicode blocks

v t e Character encodings
Early telecommunications	Telegraph code Needle Morse Non-Latin Wabun/Kana Chinese Cyrillic Baudot and Murray Fieldata ASCII ISO/IEC 646 BCDIC Teletex andVideotex/Teletext T.51/ISO/IEC 6937 ITU T.61 ITU T.101 World System Teletext background sets Transcode
ISO/IEC 8859	Approved parts -1 (Western Europe) -2 (Central Europe) -3 (Maltese/Esperanto) -4 (North Europe) -5 (Cyrillic) -6 (Arabic) -7 (Greek) -8 (Hebrew) -9 (Turkish) -10 (Nordic) -11 (Thai) -13 (Baltic) -14 (Celtic) -15 (New Western Europe) -16 (Romanian) Abandoned parts -12 (Devanagari) Proposed but not approved KOI-8 Cyrillic Sámi Adaptations Welsh Estonian Ukrainian Cyrillic
Bibliographic use	MARC-8 ANSEL CCCII/EACC ISO 5426 5426-2 5427 5428 6438 6862
National standards	ArmSCII Big5 BraSCII BSCII CNS 11643 DIN 66003 ELOT 927 GOST 10859 GB 2312 GB 12345 GB 12052 GB 18030 HKSCS ISCII JIS X 0201 JIS X 0208 JIS X 0212 JIS X 0213 KOI-7 KPS 9566 KS X 1001 KS X 1002 LST 1564 LST 1590-4 PASCII Shift JIS SI 960 TIS-620 TSCII VISCII VSCII YUSCII
ISO/IEC 2022	ISO/IEC 8859 ISO/IEC 10367 Extended Unix Code / EUC
Mac OSCode pages ("scripts")	Armenian Arabic Barents Cyrillic Celtic Central European Croatian Cyrillic Devanagari Farsi (Persian) Font X (Kermit) Gaelic Georgian Greek Gujarati Gurmukhi Hebrew Iceland Inuit Keyboard Latin (Kermit) Maltese/Esperanto Ogham Roman Romanian Sámi Turkish Turkic Cyrillic Ukrainian VT100
DOS code pages	437 737 850 858 861 862 863 864 865 866 867 868 869 899 904 932 936 942 949 950 951 1040 1043 1046 1098 1115 1116 1117 1118 1127 ABICOMP CS Indic CSX Indic CSX+ Indic CWI-2 Iran System Kamenický Mazovia MIK
IBM AIX code pages	895 896 912 915 921 922 1006 1008 1009 1010 1012 1013 1014 1015 1016 1017 1018 1019 1046 1133
Windows code pages	CER-GS 932 936 (GBK) 950 Extended Latin-8 1250 1251 1252 1253 1254 1255 1256 1257 1258 1270 Cyrillic + French Cyrillic + German Polytonic Greek
EBCDIC code pages	Japanese language in EBCDIC DKOI
DEC terminals (VTx)	Multinational (MCS) National Replacement (NRCS) French Canadian Swiss Spanish United Kingdom Dutch Finnish French Norwegian and Danish Swedish Norwegian and Danish (alternative) 8-bit Greek 8-bit Turkish SI 960 Hebrew Special Graphics Technical (TCS)
Platform specific	1052 1053 1054 1055 1058 Acorn RISC OS Amstrad CPC Apple II ATASCII Atari ST BICS Casio calculators CDC Compucolor 8001 Compucolor II CP/M+ DEC RADIX 50 DEC MCS/NRCS DG International Galaksija GEM GSM 03.38 HP Roman HP FOCAL HP RPL SQUOZE LICS LMBCS MSX NEC APC NeXT PETSCII PostScript Standard PostScript Latin 1 SAM Coupé Sega SC-3000 Sharp calculators Sharp MZ Sinclair QL Teletext TI calculators TRS-80 Ventura International WISCII XCCS ZX80 ZX81 ZX Spectrum
Unicode /ISO/IEC 10646	UTF-1 UTF-7 UTF-8 UTF-16 UTF-32 UTF-EBCDIC GB 18030 DIN 91379 BOCU-1 CESU-8 SCSU TACE16 Comparison of Unicode encodings
TeX typesetting system	Cork LY1 OML OMS OT1
Miscellaneous code pages	ABICOMP ASMO 449 Digital encoding of APL symbols ISO-IR-68 ARIB STD-B24 Fieldata HZ IEC-P27-1 INIS 7-bit 8-bit ISO-IR-169 ISO 2033 KOI KOI8-R KOI8-RU KOI8-U Mojikyō SEASCII Stanford/ITS Symbol TRON Unified Hangul Code
Control character	Morse prosigns C0 and C1 control codes ISO/IEC 6429 JIS X 0211 Unicode control, format and separator characters Whitespace characters
Related topics	CCSID Character encodings in HTML Charset detection Han unification Hardware code page MICR code Mojibake Variable-length encoding
Character sets

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