I don't know about the ext4 code specifically, but in hardware programming it is common to have stuff like "3 means 5". If for whatever reason a field of a regi

I don't know about the ext4 code specifically, but in hardware programming it is common to have stuff like "3 means 5". If for whatever reason a field of a register may only accept values that actually mean 1, 5 and 7 (to program whatever bits of the hardware, like clock divisors or whatnot), the hw register will probably only contain 2 bits, and be encoded in such a way where if you write 00b you mean 1d, if you write 01b you mean 5d and if you write 10d you mean 7. And 11b is reserved. This is a common thing, it's encoding to pack a sparse set of possible values into a few bits as you can. But then, you should probably do something such as "#define CLOCK_DIVISOR_3 0x1" instead of simply "int three = 1".