Benchmark edge cases better.

src/benchmark/benchmark.ts

@@ -1,9 +1,21 @@
+const originalGetRandomValues = globalThis.crypto.getRandomValues.bind(
+  globalThis.crypto,
+);
+
+let counter = 0;
+
+globalThis.crypto.getRandomValues = (array) => {
+  counter++;
+  return originalGetRandomValues(array);
+};
+
 import { randomUIntBelow } from "../random-uint-below";
 
 const DEFAULT_NUM_RUNS = 1_000_000;
 const DEFAULT_MAX = 1337;
 
 export function benchmark(options?: { numRuns?: number; max?: number }) {
+  counter = 0;
   const start = performance.now();
   let total = 0;
   const numRuns = options?.numRuns ?? DEFAULT_NUM_RUNS;
@@ -14,7 +26,7 @@ export function benchmark(options?: { numRuns?: number; max?: number }) {
     total += randomUIntBelow(max);
   }
   console.log(
-    `Finished ${numRuns} runs for max ${max} in: ${Math.floor((performance.now() - start) * 1000) / 1000}ms`,
+    `Finished ${numRuns} runs for max ${max} in: ${Math.floor((performance.now() - start) * 1000) / 1000}ms (${counter} calls)`,
   );
   console.log(
     `Mean of generated values (should be ≈${(max - 1) / 2}): ${total / numRuns}`,

src/benchmark/main.ts

@@ -1,6 +1,7 @@
 import { benchmark } from "./benchmark";
 
 benchmark();
-benchmark({ numRuns: 1_000_000, max: 2 ** 52 });
 benchmark({ numRuns: 1_000_000, max: 7 });
+benchmark({ numRuns: 1_000_000, max: 2 ** 52 });
+benchmark({ numRuns: 1_000_000, max: 2 ** 52 + 1 });
 benchmark({ numRuns: 1_000_000, max: 3 * 2 ** 51 });

src/random-uint-below/randomUIntBelow.ts

@@ -7,8 +7,18 @@ const MAX_JS_PRECISE_INT = 2 ** 53;
 const UPPER_HALF_MULTIPLIER = 2097152; // 2^21.
 const LOWER_HALF_RIGHT_SHIFT_BITS = 11;
 
+let counter = 0;
+
+export function resetCounter() {
+  counter = 0;
+}
+export function getCounter(): number {
+  return counter;
+}
+
 const arr = new Uint32Array(2);
 function random53BitNumber(): number {
+  counter++;
   // Construct a random 53-bit value from a 32-bit upper half and a 21-bit lower half.
   // Note that in theory it *could* be faster to construct only a 32-bit number when needed, but the impact on performance is negligible.
   globalThis.crypto.getRandomValues(arr);