Function m4ri_build_code 

pub unsafe extern "C" fn m4ri_build_code(
    ord: *mut c_int,
    inc: *mut c_int,
    l: c_int,
)

Fils var ord and var inc with Gray code dat afor a Gray code of length 2^l

ord: Will hold gray code data, must be preallocated with correct size inc: Will hold some increment data, must be preallocated with correct size l: logarithm of the length of Gray code