Fixed in Firebird 2.5.2 and 3.0.x CHAR_TO_UUID and GEN_UUID works different in big/little endian architectures

Important CHAR_TO_UUID CORE bug fix for for big-endian servers (ex: debian on IBM s390x or sparc64/powerpc) also that fixes GEN_UUID to return a compliant RFC-4122 UUID:

It has been discovered that before Firebird 2.5.2, CHAR_TO_UUID and UUID_TO_CHAR works incorrectly in big-endian servers. In these machines, bytes/characters are swapped and goes in wrong positions when converting. This bug was fixed in 2.5.2 and 3.0, but that means these functions now returns different values (for the same input parameter) than before.

ps: And here is Firebird development discussion and here is the full patch

If you want to know on what endian os you have you can check the Endianness Table