+/* This program operates by filling in a state table representing the best
+ * possible trips you could make; the ones that makes you the most money.
+ * This is feasible because we don't look at all the possible trips.
+ * We define a list of things that are germane to this game and then only
+ * consider the best outcome in each possible game state.
+ *
+ * Each cell in the table represents a state in the game. In each cell,
+ * we track two things: 1. the most money you could possibly have while in
+ * that state and 2. one possible way to get into that state with that
+ * amount of money.
+ *
+ * A basic analysis can be done with a two-dimensional table: location and
+ * fuel. planeteer-1.0 used this two-dimensional table. This version
+ * adds features mostly by adding dimensions to this table.
+ *
+ * Note that the sizes of each dimension are data driven. Many dimensions
+ * collapse to one possible value (ie, disappear) if the corresponding
+ * feature is not enabled.
+ *
+ * The order of the dimensions in the list of constants below determines
+ * their layout in RAM. The cargo-based 'dimensions' are not completely
+ * independent -- some combinations are illegal and not used. They are
+ * handled as three dimensions rather than one for simplicity. Placing
+ * these dimensions first causes the unused cells in the table to be
+ * grouped together in large blocks. This keeps them from polluting
+ * cache lines, and if they are large enough, prevent the memory manager
+ * from allocating pages for these areas at all.
+ *
+ * If the table gets too big to fit in RAM:
+ * * Combine the Edens, Cloaks, and UnusedCargo dimensions. Of the
+ * 24 combinations, only 15 are legal: a 38% savings.
+ * * Reduce the size of the Fuel dimension to 3. We only ever look
+ * backwards 2 units, so just rotate the logical values through
+ * the same 3 physical addresses. This is good for an 82% savings.
+ * * Reduce the size of the Edens dimension from 3 to 2, for the
+ * same reasons as Fuel above. 33% savings.
+ * * Buy more ram. (Just sayin'. It's cheaper than you think.)
+ *
+ */
+
+// The official list of dimensions:
+const (
+ // Name Num Size Description
+ Edens = iota // 1 3 # of Eden warp units (0 - 2 typically)
+ Cloaks // 2 2 # of Devices of Cloaking (0 or 1)
+ UnusedCargo // 3 4 # of unused cargo spaces (0 - 3 typically)
+ Fuel // 4 17 Reactor power left (0 - 16)
+ Location // 5 26 Location (which planet)
+ Hold // 6 15 Cargo bay contents (a *Commodity or nil)
+ NeedFighters // 7 2 Errand: Buy fighter drones (needed or not)
+ NeedShields // 8 2 Errand: Buy shield batteries (needed or not)
+ Visit // 9 2**N Visit: Stop by these N planets in the route
+
+ NumDimensions
+)
+
+func bint(b bool) int {
+ if b {
+ return 1
+ }
+ return 0
+}
+
+func DimensionSizes(data planet_data) []int {
+ eden_capacity := data.Commodities["Eden Warp Units"].Limit
+ if *start_edens > eden_capacity {
+ eden_capacity = *start_edens
+ }
+ cloak_capacity := bint(*cloak)
+ dims := make([]int, NumDimensions)
+ dims[Edens] = eden_capacity + 1
+ dims[Cloaks] = cloak_capacity + 1
+ dims[UnusedCargo] = eden_capacity + cloak_capacity + 1
+ dims[Fuel] = *fuel + 1
+ dims[Location] = len(data.Planets)
+ dims[Hold] = len(data.Commodities) + 1
+ dims[NeedFighters] = bint(*drones > 0) + 1
+ dims[NeedShields] = bint(*batteries > 0) + 1
+ dims[Visit] = 1 << uint(len(visit()))
+
+ // Remind myself to add a line above when adding new dimensions
+ for i, dim := range dims {
+ if dim < 1 {
+ panic(i)
+ }
+ }
+ return dims
+}
+
+func StateTableSize(dims []int) int {
+ product := 1
+ for _, size := range dims {
+ product *= size
+ }
+ return product
+}
+
+type State struct {
+ value, from int
+}
+
+func EncodeIndex(dims, addr []int) int {
+ index := addr[0]
+ if addr[0] > dims[0] {
+ panic(0)
+ }
+ for i := 1; i < NumDimensions; i++ {
+ if addr[i] > dims[i] {
+ panic(i)
+ }
+ index = index*dims[i] + addr[i]
+ }
+ return index
+}
+
+func DecodeIndex(dims []int, index int) []int {
+ addr := make([]int, NumDimensions)
+ for i := NumDimensions - 1; i > 0; i-- {
+ addr[i] = index % dims[i]
+ index /= dims[i]
+ }
+ addr[0] = index
+ return addr
+}
+
+func InitializeStateTable(data planet_data, dims []int) []State {
+ table := make([]State, StateTableSize(dims))
+
+ addr := make([]int, NumDimensions)
+ addr[Fuel] = *fuel
+ addr[Edens] = *start_edens
+ addr[Location] = data.p2i[*start]
+ table[EncodeIndex(dims, addr)].value = *funds
+
+ return table
+}
+
+/* These four fill procedures fill in the cell at address addr by
+ * looking at all the possible ways to reach this cell and selecting
+ * the best one.
+ *
+ * The other obvious implementation choice is to do this the other way
+ * around -- for each cell, conditionally overwrite all the other cells
+ * that are reachable *from* the considered cell. We choose gathering
+ * reads over scattering writes to avoid having to take a bunch of locks.
+ */
+
+func UpdateCell(table []State, here, there, value_difference int) {
+ possible_value := table[there].value + value_difference
+ if table[there].value > 0 && possible_value > table[here].value {
+ table[here].value = possible_value
+ table[here].from = there
+ }
+}
+
+func FillCellByArriving(data planet_data, dims []int, table []State, addr []int) {
+ my_index := EncodeIndex(dims, addr)
+ other := make([]int, NumDimensions)
+ copy(other, addr)
+
+ /* Travel here via a 2-fuel unit jump */
+ if addr[Fuel]+2 < dims[Fuel] {
+ other[Fuel] = addr[Fuel] + 2
+ for other[Location] = 0; other[Location] < dims[Location]; other[Location]++ {
+ if data.Planets[data.i2p[addr[Location]]].BeaconOn {
+ UpdateCell(table, my_index, EncodeIndex(dims, other), 0)
+ }
+ }
+ other[Location] = addr[Location]
+ other[Fuel] = addr[Fuel]
projects / planeteer / blobdiff