Replace string conversion with prime multiplication in hash

It's benchmarking about 67% faster without any degradation in uniformity.

Also fixed some tests that were assuming some things about hashing.

packages/core/graph/src/AdjacencyList.js

@@ -1099,19 +1099,15 @@ export default class AdjacencyList<TEdgeType: number = 1> {
    *
    */
   hash(from: NodeId, to: NodeId, type: TEdgeType | NullEdgeType): EdgeHash {
-    // A crude multiplicative hash, in 3 steps:
-    // 1. Serialize the args into an integer that reflects the argument order,
-    // shifting the magnitude of each argument by the sum
-    // of the significant digits of the following arguments,
-    // .e.g., `hash(10, 24, 4) => 10244`.
-    // $FlowFixMe[unsafe-addition]
-    // $FlowFixMe[incompatible-type]
-    let hash = '' + from + to + type - 0;
-    // 2. Mix the upper bits of the integer into the lower bits.
-    // We do this to increase the likelihood that a change to any
-    // bit of the input will vary the output widely.
-    hash = hash32shift(hash);
-    // 3. Map the hash to a value modulo the edge capacity.
+    // Each parameter is hashed by mixing its upper bits into its lower bits to
+    // increase the likelihood that a change to any bit of the input will vary
+    // the output widely. Then we do a series of prime multiplications and
+    // additions to combine the hashes into one value.
+    let hash = 17;
+    hash = hash * 37 + hash32shift((from: any));
+    hash = hash * 37 + hash32shift((to: any));
+    hash = hash * 37 + hash32shift((type: any));
+    // Finally, we map the hash to a value modulo the edge capacity.
     hash %= this.#edges[CAPACITY];
     return hash;
   }

packages/core/graph/test/AdjacencyList.test.js

@@ -193,10 +193,13 @@ describe('AdjacencyList', () => {
   });
 
   it('addEdge should not replace a deleted edge if the edge was already added', () => {
-    let graph = new AdjacencyList();
     // Mock hash fn to generate collisions
+    // $FlowFixMe[method-unbinding]
+    let originalHash = AdjacencyList.prototype.hash;
     // $FlowFixMe[cannot-write]
-    graph.hash = () => 1;
+    AdjacencyList.prototype.hash = () => 1;
+
+    let graph = new AdjacencyList();
     let n0 = graph.addNode();
     let n1 = graph.addNode();
     let n2 = graph.addNode();
@@ -210,26 +213,42 @@ describe('AdjacencyList', () => {
     graph.addEdge(n0, n1, 1);
     assert(!graph.serialize().edges[index]);
     assert(graph.stats.edges === 1);
+
+    // $FlowFixMe[cannot-write]
+    AdjacencyList.prototype.hash = originalHash;
   });
 
   it('addEdge should replace a deleted edge', () => {
-    let graph = new AdjacencyList({edgeCapacity: 2});
     // Mock hash fn to generate collisions
+    // $FlowFixMe[method-unbinding]
+    let originalHash = AdjacencyList.prototype.hash;
     // $FlowFixMe[cannot-write]
-    graph.hash = () => 1;
+    AdjacencyList.prototype.hash = () => 1;
+
+    let graph = new AdjacencyList();
     let n0 = graph.addNode();
     let n1 = graph.addNode();
-    graph.addEdge(n0, n1, 1);
     graph.addEdge(n0, n1, 2);
     // $FlowFixMe[incompatible-type]
     let index: number = graph.indexOf(n0, n1, 2);
-    assert(graph.serialize().edges[index] > 0);
     assert(graph.serialize().edges[index]);
     graph.removeEdge(n0, n1, 2);
     assert(!graph.serialize().edges[index]);
     graph.addEdge(n0, n1, 2);
-    assert(graph.serialize().edges[index] > 0);
-    assert(graph.serialize().edges[index]);
+    // $FlowFixMe[incompatible-type]
+    let index2: number = graph.indexOf(n0, n1, 2);
+    assert(!graph.serialize().edges[index]);
+    assert(graph.serialize().edges[index2]);
+    // Resize to reclaim deleted edge space.
+    graph.resizeEdges(4);
+    // $FlowFixMe[incompatible-type]
+    let index3: number = graph.indexOf(n0, n1, 2);
+    assert(!graph.serialize().edges[index]);
+    assert(!graph.serialize().edges[index2]);
+    assert(graph.serialize().edges[index3]);
+
+    // $FlowFixMe[cannot-write]
+    AdjacencyList.prototype.hash = originalHash;
   });
 
   describe('deserialize', function() {