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5. Leading Periods: In the event that there do not exist any characters
prior to the first “.” (#002E) character, leading “.” (#002E) characters
shall be disregarded up to the first non “.” (#002E) character, in the
application of this heuristic.
6. Multiple Periods: In the event that the FileIdentifier contains multiple
“.” (#002E) characters, all characters appearing subsequent to the last
‘.’ (#002E) shall be considered as constituting the file extension if and
only if it is less than or equal to 5 characters in length, otherwise the
file extension shall not exist. Characters appearing prior to the file
extension, excluding the last ‘.’ (#002E), shall be considered as
constituting the file name. All embedded “.” (#002E) characters
within the file name shall be removed.
7. Long Extension: In the event that the number of characters constituting
the file extension at this step in the process is greater than 3, the file
extension shall be regarded as having been composed of the first 3
characters amongst the characters constituting the file extension at this
step in the process.
8. Long Filename: In the event that the number of characters constituting
the file name at this step in the process is greater than 8, the file name
shall be truncated to 4 characters.
9. FileIdentifier CRC: Since through the above process character
information from the original FileIdentifier is lost the chance of
creating a duplicate FileIdentifier in the same directory increases. To
greatly reduce the chance of having a duplicate FileIdentifier the file
name shall be modified to contain a CRC of the original FileIdentifier.
The file name shall be composed of the first 4 characters constituting
the file name at this step in the process, followed by the separator ‘#’
(#0023), followed by the 3 digit CS0 Base41 representation of the 16-
bit CRC of the UNICODE expansion of the original filename.
10. The new file identifier shall be translated to all upper case.
4.2.2.1.2 OS/2
Due to the restrictions imposed by the OS/2 operating system environment, on the
FileIdentifier associated with a file the following methodology shall be employed
to handle FileIdentifier(s) under the above-mentioned operating system
environment:
1. FileIdentifier Lookup: Upon request for a “lookup” of a FileIdentifier,
a case-sensitive comparison may be performed. If the case-sensitive
comparison is not done or if it fails, a case-insensitive comparison
shall be performed.
2. Validate FileIdentifer: If the FileIdentifier is a valid OS/2 file
identifier then do not apply the following steps.
UDF 2.01
102
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