RULE: The bit manipulation routines IAND, IOR, IEOR, NOT, ISHFT, IBITS, IBSET, BTEST, IBCLR AND ISHTFC are permitted. Versions are available from the CERN General Library for those machines that don't have compiler support for them. Note: it is not possible to force all compilers to use the CERN routines by declaring them as EXTERNAL; the CERN library only supplies them for those compilers that don't have them. However, the type of each function must be declared. The code must not make any assumption about the value of the carry-ins when bit shifting.