In b5ff87ca71, I made a number of adjustments to our conversion code
for CP1252. One of the adjustments was to make the mappings match those
published by the Unicode Consortium in the file CP1252.TXT. These do
not include mappings for the CP1252 bytes 0x81, 0x8D, 0x8F, 0x90, and
0x9D.
Rostyslav Gulka reported that this caused a problem. His application
stores binary JPEG data in an MS-SQL database. When they SELECT the
binary data out of the database, it is treated as CP1252 text and
automatically converted to UTF-8. To recover the original binary
data, they then do a conversion from UTF-8 to CP1252.
Obviously, that does not work if certain CP1252 bytes do not map to
any Unicode codepoint at all.
While this is a very unusual application of text encoding conversion,
and we might choose not to support it if there was no other basis for
including those mappings, it seems that Microsoft does actually include
them in the Win32 API as "best fit" mappings. These are extra mappings
from Unicode to other text encodings, which the Win32 API function
WideCharToMultiByte uses by default unless the WC_NO_BEST_FIT_CHARS
flag was passed.
A list of these "best fit" mappings for CP1252 can be found here:
https://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WindowsBestFit/bestfit1252.txt
a1a69c3734