feat: yaaay first stem

packages/utils/src/fastHash.test.ts

@@ -0,0 +1,54 @@
+import { test, expect } from 'vitest';
+import { fastHashArray, fastHashString } from './fastHash';
+
+test('fastHashString doesnt produce clashes', () => {
+  const hashA = fastHashString('abcdef');
+  const hashB = fastHashString('abcdeg');
+  const hashC = fastHashString('abcdeg');
+
+  expect(hashA).not.toEqual(hashB);
+  expect(hashB).toEqual(hashC);
+});
+
+test("fastHashArray doesnt product collisions", () => {
+
+  const a = new Int32Array(1000);
+
+  const hash_a = fastHashArray(a);
+  a[0] = 1;
+
+  const hash_b = fastHashArray(a);
+
+  expect(hash_a).not.toEqual(hash_b);
+
+});
+
+test('fastHashArray is fast(ish) < 20ms', () => {
+
+  const a = new Int32Array(10_000);
+
+  const t0 = performance.now();
+  fastHashArray(a);
+
+  const t1 = performance.now();
+
+  a[0] = 1;
+
+  fastHashArray(a);
+
+  const t2 = performance.now();
+
+  expect(t1 - t0).toBeLessThan(20);
+  expect(t2 - t1).toBeLessThan(20);
+});
+
+// test if the fastHashArray function is deterministic
+test('fastHashArray is deterministic', () => {
+  const a = new Int32Array(1000);
+  a[42] = 69;
+  const b = new Int32Array(1000);
+  b[42] = 69;
+  const hashA = fastHashArray(a);
+  const hashB = fastHashArray(b);
+  expect(hashA).toEqual(hashB);
+});