id 0 reserver

README.md

@@ -4,7 +4,9 @@ go-hnsw is a GO implementation of the HNSW approximate nearest-neighbour search
 
 ## Usage
 
-Simple usage example. Note that both index building and searching can be safely done in parallel with multiple goroutines. 
+Simple usage example. See examples folder for more.
+Note that both index building and searching can be safely done in parallel with multiple goroutines.
+You can always extend the index, even while searching.
 
 ```go
 package main
@@ -31,10 +33,11 @@ func main() {
 	h := hnsw.New(M, efConstruction, &zero)
 	h.Grow(10000)
 
-	for i := 0; i < 10000; i++ {
+    // Note that added ID:s must start from 1
+	for i := 1; i <= 10000; i++ {
 		h.Add(randomPoint(), uint32(i))
-		if (i+1)%1000 == 0 {
-			fmt.Printf("%v points added\n", i+1)
+		if (i)%1000 == 0 {
+			fmt.Printf("%v points added\n", i)
 		}
 	}
 

hnsw.go

@@ -256,15 +256,19 @@ func (h *Hnsw) Grow(size int) {
 
 func (h *Hnsw) Add(q *Point, id uint32) {
 
+	if id == 0 {
+		panic("Id 0 is reserved, use ID:s starting from 1 when building index")
+	}
+
 	// generate random level
 	curlevel := int(math.Floor(-math.Log(rand.Float64() * h.LevelMult)))
 
 	epID := h.enterpoint
 	currentMaxLayer := h.nodes[epID].level
 	ep := &distqueue.Item{ID: h.enterpoint, D: DistFast(h.nodes[h.enterpoint].p, q)}
 
-	// Preassigned id (starting from 0), assume Grow has been called in advance
-	newID := uint32(id + 1)
+	// assume Grow has been called in advance
+	newID := id
 	newNode := node{p: q, level: curlevel, friends: make([][]uint32, min(curlevel, currentMaxLayer)+1)}
 
 	// first pass, find another ep if curlevel < maxLayer
@@ -419,7 +423,6 @@ func (h *Hnsw) Search(q *Point, ef int, K int) *distqueue.DistQueueClosestLast {
 	for resultSet.Len() > K {
 		resultSet.Pop()
 	}
-	// actually we should fix the id since our returned ids start from 1
 	return resultSet
 }