add return bool to indicate changed

common.go

@@ -18,7 +18,13 @@ func (p sortableSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
 
 type set map[uint32]bool
 
-func (s set) Add(i uint32) { s[i] = true }
+func (s set) Add(i uint32) bool {
+	if s[i] {
+		return false
+	}
+	s[i] = true
+	return true
+}
 
 func alpha(m uint32) float64 {
 	if m == 16 {

hyperloglog.go

@@ -45,15 +45,18 @@ func (h *HyperLogLog) Clear() {
 }
 
 // Add adds a new item to HyperLogLog h.
-func (h *HyperLogLog) Add(item Hash32) {
+func (h *HyperLogLog) Add(item Hash32) bool {
 	x := item.Sum32()
 	i := eb32(x, 32, 32-h.p) // {x31,...,x32-p}
 	w := x<<h.p | 1<<(h.p-1) // {x32-p,...,x0}
 
+	changed := false
 	zeroBits := clz32(w) + 1
 	if zeroBits > h.reg[i] {
 		h.reg[i] = zeroBits
+		changed = true
 	}
+	return changed
 }
 
 // Merge takes another HyperLogLog and combines it with HyperLogLog h.

hyperloglogplus.go

@@ -144,20 +144,25 @@ func (h *HyperLogLogPlus) toNormal() {
 }
 
 // Add adds a new item to HyperLogLogPlus h.
-func (h *HyperLogLogPlus) Add(item Hash64) {
+func (h *HyperLogLogPlus) Add(item Hash64) bool {
 	x := item.Sum64()
+	changed := false
 	if h.sparse {
-		h.tmpSet.Add(h.encodeHash(x))
-		h.maybeMerge()
+		changed = h.tmpSet.Add(h.encodeHash(x))
+		if changed {
+			h.maybeMerge()
+		}
 	} else {
 		i := eb64(x, 64, 64-h.p) // {x63,...,x64-p}
 		w := x<<h.p | 1<<(h.p-1) // {x63-p,...,x0}
 
 		zeroBits := clz64(w) + 1
 		if zeroBits > h.reg[i] {
 			h.reg[i] = zeroBits
+			changed = true
 		}
 	}
+	return changed
 }
 
 // Merge takes another HyperLogLogPlus and combines it with HyperLogLogPlus h.