X rebuild: tests: Precompute kadj10·kadj21

82s -> 75s.

wcfs/internal/xbtree/δbtail_test.go

@@ -542,6 +542,23 @@ func (kadj KAdjMatrix) Map(keys SetKey) SetKey {
 	return res
 }
 
+// Mul returns kadjA·kadjB .
+//
+// (kadjA·kadjB).Map(keys) = kadjA.Map(kadjB.Map(keys))
+func (kadjA KAdjMatrix) Mul(kadjB KAdjMatrix) KAdjMatrix {
+	// ~ assert kadjA.keys == kadjB.keys
+	// check only len here; the rest will be asserted by Map
+	if len(kadjA) != len(kadjB) {
+		panicf("kadj.Mul: different keys:\n\nkadjA: %v\nkadjB: %v", kadjA, kadjB)
+	}
+
+	kadj := make(KAdjMatrix, len(kadjB))
+	for k, tob := range kadjB {
+		kadj[k] = kadjA.Map(tob)
+	}
+	return kadj
+}
+
 // KAdj computes adjacency matrix for t1 -> t2 transition.
 //
 // The set of keys for which kadj matrix is computed can be optionally provided.
@@ -962,6 +979,9 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 		kadj21 := KAdj(t2,t1, allTestKeys(t0,t1,t2))
 		kadj12 := KAdj(t1,t2, allTestKeys(t0,t1,t2))
 
+		// kadj210 = kadj10·kadj21
+		kadj210 := kadj10.Mul(kadj21)
+
 		ø := PPTreeSubSet{}
 
 		// verify t0 -> t1 Track(keys1) Rebuild -> t2 Track(keys2) Rebuild
@@ -1008,7 +1028,7 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 					// Update()  (which includes rebuild)
 					keys1R2 := kadj12.Map(keys1)
 					for {
-						keys1R2_ := kadj10.Map(kadj21.Map(keys1R2))
+						keys1R2_ := kadj210.Map(keys1R2)
 						if keys1R2.Equal(keys1R2_) {
 							break
 						}
@@ -1046,7 +1066,7 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 						// Track(keys2) + rebuild
 						keys12R2 := keys1R2.Union(keys2)
 						for {
-							keys12R2_ := kadj10.Map(kadj21.Map(keys12R2))
+							keys12R2_ := kadj210.Map(keys12R2)
 							if keys12R2.Equal(keys12R2_) {
 								break
 							}