UTF-8 space efficiency

Kragen Sitaker kragen at pobox.com
Sat Nov 13 17:04:49 GMT 1999

UTF-8 requires:
- 1 byte each for the ASCII characters (U+0000 to U+007F), known as the
  "Basic Latin" block in Unicode.  This is better than UTF-16, and no
  worse than ASCII.
- 2 bytes each for characters from U+0080 to U+07FF.  This includes Latin-1,
  Latin Extended-A, Latin Extended-B, the IPA extensions, spacing
  modifier letters, combining diacritical marks, Greek, Cyrillic,
  Armenian, Hebrew, and Arabic.  This is no worse than UTF-16.
- 3 bytes each for U+0800 to U+FFFF.  This is worse than UTF-16, and it covers
  the vast majority of Unicode characters in use today.
- 4 bytes each for U+10000 to U+10FFFF.  This is no worse than UTF-16,
  and it potentially covers many more characters than in all the
  previous ranges put together, but it is currently nearly unused.  In
  the future, it is likely to be used only for extremely unusual
  scripts, such as Sumerian cuneiform, the Tengwar of Feanor, Egyptian
  hieroglyphics, hieratic, and demotic.  So I doubt this will be of
  much import to many people.

UTF-8 has some other advantages over UTF-16.  It has no byte-order
ambiguity, and for many purposes -- such as string-searching -- it can
be treated as simply a string of bytes.  And it's "filesystem-safe",
which means you can use it in filenames without modifying the
filesystem to be Unicode-aware.

>From my provincial American point of view, it looks like a space win,
too -- most of my text is ASCII anyway.  Obviously if I were mostly
using one of the numerous scripts in the UTF-8-disadvantaged area, I
might feel differently.

But to tell the truth, most of the space on my disk and bandwidth on my
modem isn't consumed by text, anyway.  A 50% increase in the size of
all that text wouldn't bother me much.

<kragen at pobox.com>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
The Internet stock bubble didn't burst on 1999-11-08.  Hurrah!

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