gistfile1.lua

function putb(buf, type, where, what)
   local bp = ffi.cast('uint8_t*', buf)
   local ptr = ffi.cast(type..'*', bp + where)
   ptr[0] = what
end

function getb(buf, type, where)
   local bp = ffi.cast('uint8_t*', buf)
   return ffi.cast(type..'*', bp + where)[0]
end