Fixed bug #896
authorSam Lantinga <slouken@libsdl.org>
Fri, 11 Dec 2009 08:03:43 +0000
changeset 3539f2846bf19360
parent 3538 a1896642a47e
child 3540 3ad09fdbfcb0
Fixed bug #896

John Popplewell 2009-12-08 23:05:50 PST

Originally reported by AKFoerster on the mailing list.

Error decoding UTF8 Russian text to UTF-16LE on Windows, but specifically on
platforms without iconv support (the default on Windows).

Valid UTF8 characters are flagged as being overlong and then substituted by the
UNKNOWN_UNICODE character.

After studying the testiconv.c example program, reading the RFCs and putting
some printf statements in SDL_iconv.c the problem is in a test for 'Maximum
overlong sequences', specifically 4.2.1, which is carried out by the following
code:

} else if ( p[0] >= 0xC0 ) {
if ( (p[0] & 0xE0) != 0xC0 ) {
/* Skip illegal sequences
return SDL_ICONV_EILSEQ;
*/
ch = UNKNOWN_UNICODE;
} else {
if ( (p[0] & 0xCE) == 0xC0 ) { <<<<<<<< here
overlong = SDL_TRUE;
}
ch = (Uint32)(p[0] & 0x1F);
left = 1;
}
} else {

Here is the 2-byte encoding of a character in range 00000080 - 000007FF
110xxxxx 10xxxxxx

The line in question is supposed to be checking for an overlong sequence which
would be less than
11000001 10111111

which should be represented as a single byte.

BUT, the mask value (0xCE) is wrong, it isn't checking the top-most bit:
11000001 value
11001110 mask (incorrect)
^
and should be (0xDE):
11000001 value
11011110 mask (correct)

making the above code:

} else if ( p[0] >= 0xC0 ) {
if ( (p[0] & 0xE0) != 0xC0 ) {
/* Skip illegal sequences
return SDL_ICONV_EILSEQ;
*/
ch = UNKNOWN_UNICODE;
} else {
if ( (p[0] & 0xDE) == 0xC0 ) { <<<<<<<< here
overlong = SDL_TRUE;
}
ch = (Uint32)(p[0] & 0x1F);
left = 1;
}
} else {

I can supply a test program and/or a patch if required,

best regards,
John Popplewell
src/stdlib/SDL_iconv.c
     1.1 --- a/src/stdlib/SDL_iconv.c	Thu Dec 10 09:27:23 2009 +0000
     1.2 +++ b/src/stdlib/SDL_iconv.c	Fri Dec 11 08:03:43 2009 +0000
     1.3 @@ -391,7 +391,7 @@
     1.4                           */
     1.5                          ch = UNKNOWN_UNICODE;
     1.6                      } else {
     1.7 -                        if ((p[0] & 0xCE) == 0xC0) {
     1.8 +                        if ((p[0] & 0xDE) == 0xC0) {
     1.9                              overlong = SDL_TRUE;
    1.10                          }
    1.11                          ch = (Uint32) (p[0] & 0x1F);