2 * superset.c: deal with character sets which are supersets of
9 * Just in case it's ever useful again, this rather simplistic
10 * piece of Perl/sh analyses sbcs.dat and determines which pairs of
11 * character sets are identical in the A0-FF region. This doesn't
12 * prove supersethood, but it spots obvious cases.
14 perl -ne '/^[^ ]{4} / and defined ($line) and $line < 16 and do {' \
15 -e ' chomp; print " $_" if $line>=10; print "\n" if ++$line==16; };' \
16 -e '/^charset (.*)$/ and do { $line = 0; printf "%30s:", $1; };' \
17 sbcs.dat | sort +1 | uniq -f1 -D
19 * When run on sbcs.dat rev 1.3, it reports only two sets of matches:
21 * - ISO8859_1, ISO8859_1_X11 and CP1252 all match.
22 * - ISO8859_4 and CP1254 match.
24 * FIXME: There is more to it than this, and in particular there's
25 * even more to it than simple subsethood. Look at CP1255 and
26 * ISO8859_8: they match at every code point defined in both, but
27 * they each define at least one code point the other doesn't. It
28 * isn't clear how I should handle this. The right thing might be
29 * to define yet another SBCS which is the union of both, and
30 * upgrade both to that. Or it might be that the unicode.org
31 * mapping table for CP1255 is simply out of date, and the mapping
32 * ISO8859_8 has which it doesn't (DF -> U+2017 DOUBLE LOW LINE)
33 * should be present in it too, which would make it a proper
34 * superset of ISO8859_8 and solve the problem.
36 * However, for the moment I'm satisfied with enhancing this table
37 * as and when necessary; the idea is not to include _all_ superset
38 * relations here, the idea is to spot charset IDs which are used
39 * _in practice_ to mean other charset IDs. So unless and until I
40 * find out that there really is confusion between ISO8859_8 and
41 * CP1255, I don't need to do anything about it here.
44 int charset_upgrade(int charset
)
46 if (charset
== CS_ASCII
|| charset
== CS_ISO8859_1
)
48 if (charset
== CS_ISO8859_4
)
50 if (charset
== CS_EUC_KR
)
56 * This function returns TRUE if the input charset is a vaguely
57 * sensible superset of ASCII. That is, it returns FALSE for 7-bit
58 * encoding formats such as HZ and UTF-7.
60 int charset_contains_ascii(int charset
)
62 return (charset
!= CS_HZ
&&
64 charset
!= CS_UTF7_CONSERVATIVE
);