Do log2 of the value.
Env_Flags :: distinct bit_set[Env_Flag; c.uint]
Env_Flag :: enum c.uint {
FIXEDMAP = 0,
NOSUBDIR = 14,
RDONLY = 17,
WRITEMAP = 19,
NOMETASYNC = 18,
NOSYNC = 16,
MAPASYNC = 20,
NOTLS = 21,
NOLOCK = 22,
NORDAHEAD = 23,
NOMEMINIT = 24,
PREVSNAPSHOT = 25,
}