This is interesting (in a morbid sort of way)...

Is 'subkey' initialized in another translation unit? (Clang is weak in
inter-translation unit analysis). I suspect if there was an actual problem
below, then it would have been seen already...

libtool: compile: /usr/local/bin/scan-build/ccc-analyzer -DHAVE_CONFIG_H -I.
-I.. -I../src -I../src -I/usr/local/include -g3 -O1 -fvisibility=hidden -Wall
-MT des.lo -MD -MP -MF .deps/des.Tpo -c des.c -o des.o

des.c:630:3: warning: The right operand of '^' is a garbage value

DES_ROUND (right, left, work, keys) DES_ROUND (left, right, work, keys)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

des.c:444:17: note: expanded from macro 'DES_ROUND'

work = from ^ *subkey++;                            \
            ^ ~~~~~~~~~

1 warning generated.