There are no current middle-endian systems but they used to exist. The PDP-11 is the most famous one. The macros would work on all systems, but as only very old

There are no current middle-endian systems but they used to exist. The PDP-11 is the most famous one. The macros would work on all systems, but as only very old systems are middle-endian, they also have old compilers so may not be able to optimise it as well.