func GetField(L *luajit.State, f string) (float64, bool) {
var result float64
L.Pushstring(f)
L.Gettable(-2)
if L.Isnumber(-1) != true {
print("invalid field in table")
return 0, false
}
result = L.Tonumber(-1)
L.Pop(1)
return result, true
}
