Don't use 0 for uninitialized indexes

0 is a valid index.  It can legitimately be the head of the optimal
path.  When it was the head of the optimal path, DescribePath() would
print nothing.  This fixes that bug.

diff --git a/planeteer.go b/planeteer.go
index 67a843dd400c9ca3d8e708af48d0850442b91c4f..e3c04cfb3bd9690bbd5e465605240b788b34c6fc 100644 (file)
--- a/planeteer.go
+++ b/planeteer.go
@@ -241,9 +241,11 @@ type State struct {
 }
 
 const (
-       CELL_UNINITIALIZED = -2147483647 + iota
-       CELL_BEING_EVALUATED
-       CELL_RUBISH
+       FROM_ROOT = -2147483647 + iota
+       FROM_UNINITIALIZED
+       VALUE_UNINITIALIZED
+       VALUE_BEING_EVALUATED
+       VALUE_RUBISH
 )
 
 func EncodeIndex(dims, addr []int) int32 {
@@ -273,7 +275,8 @@ func DecodeIndex(dims []int, index int32) []int {
 func CreateStateTable(data planet_data, dims []int) []State {
        table := make([]State, StateTableSize(dims))
        for i := range table {
-               table[i].value = CELL_UNINITIALIZED
+               table[i].value = VALUE_UNINITIALIZED
+               table[i].from = FROM_UNINITIALIZED
        }
 
        addr := make([]int, NumDimensions)
@@ -281,7 +284,9 @@ func CreateStateTable(data planet_data, dims []int) []State {
        addr[Edens] = *start_edens
        addr[Location] = data.p2i[*start]
        addr[Traded] = 1
-       table[EncodeIndex(dims, addr)].value = int32(*funds)
+       start_index := EncodeIndex(dims, addr)
+       table[start_index].value = int32(*funds)
+       table[start_index].from = FROM_ROOT
 
        return table
 }
@@ -306,15 +311,15 @@ var cell_filled_count int
 
 func CellValue(data planet_data, dims []int, table []State, addr []int) int32 {
        my_index := EncodeIndex(dims, addr)
-       if table[my_index].value == CELL_BEING_EVALUATED {
+       if table[my_index].value == VALUE_BEING_EVALUATED {
                panic("Circular dependency")
        }
-       if table[my_index].value != CELL_UNINITIALIZED {
+       if table[my_index].value != VALUE_UNINITIALIZED {
                return table[my_index].value
        }
-       table[my_index].value = CELL_BEING_EVALUATED
+       table[my_index].value = VALUE_BEING_EVALUATED
 
-       best_value := int32(CELL_RUBISH)
+       best_value := int32(VALUE_RUBISH)
        best_source := make([]int, NumDimensions)
        other := make([]int, NumDimensions)
        copy(other, addr)
@@ -505,7 +510,7 @@ func CellValue(data planet_data, dims []int, table []State, addr []int) int32 {
 
        // Sanity check: This cell was in state BEING_EVALUATED
        // the whole time that it was being evaluated.
-       if table[my_index].value != CELL_BEING_EVALUATED {
+       if table[my_index].value != VALUE_BEING_EVALUATED {
                panic(my_index)
        }
 
@@ -566,7 +571,10 @@ func Commas(n int32) (s string) {
 }
 
 func DescribePath(data planet_data, dims []int, table []State, start int32) (description []string) {
-       for index := start; index > 0 && table[index].from > 0; index = table[index].from {
+       for index := start; table[index].from > FROM_ROOT; index = table[index].from {
+               if table[index].from == FROM_UNINITIALIZED {
+                       panic(index)
+               }
                var line string
                addr := DecodeIndex(dims, index)
                prev := DecodeIndex(dims, table[index].from)