From c26cc0350bfde58d227cf7507b675abcc306aeea Mon Sep 17 00:00:00 2001
From: Lumi Pakkanen <lumi.pakkanen@gmail.com>
Date: Sat, 13 Jan 2024 12:59:08 +0200
Subject: [PATCH] Implement ceiling power of two

---
 src/__tests__/index.spec.ts | 27 +++++++++++++++++++++++++++
 src/index.ts                | 15 +++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/src/__tests__/index.spec.ts b/src/__tests__/index.spec.ts
index 005b406..05c3407 100644
--- a/src/__tests__/index.spec.ts
+++ b/src/__tests__/index.spec.ts
@@ -2,6 +2,7 @@ import {describe, it, expect} from 'vitest';
 import {
   arraysEqual,
   binomial,
+  ceilPow2,
   circleDifference,
   circleDistance,
   clamp,
@@ -152,3 +153,29 @@ describe('Pitch distance with circle equivalence', () => {
     expect(diff).toBeCloseTo(247.741);
   });
 });
+
+describe('Ceiling power of two', () => {
+  it('works with small values', () => {
+    const x = 1 + Math.random() * (2 ** 30 - 2);
+    const p2 = ceilPow2(x);
+    expect(x).toBeLessThanOrEqual(p2);
+    expect(p2).toBeLessThan(2 * x);
+    expect(Math.log2(p2)).toBeCloseTo(Math.round(Math.log2(p2)));
+  });
+
+  it('works with tiny values', () => {
+    const x = Math.random();
+    const p2 = ceilPow2(x);
+    expect(x).toBeLessThanOrEqual(p2);
+    expect(p2).toBeLessThan(2 * x);
+    expect(Math.log2(p2)).toBeCloseTo(Math.round(Math.log2(p2)));
+  });
+
+  it('works with large values', () => {
+    const x = 2 ** 31 + Math.random() * 2 ** 37;
+    const p2 = ceilPow2(x);
+    expect(x).toBeLessThanOrEqual(p2);
+    expect(p2).toBeLessThan(2 * x);
+    expect(Math.log2(p2)).toBeCloseTo(Math.round(Math.log2(p2)));
+  });
+});
diff --git a/src/index.ts b/src/index.ts
index 794f255..93a7849 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -284,3 +284,18 @@ export function circleDifference(a: number, b: number, equaveCents = 1200.0) {
 export function circleDistance(a: number, b: number, equaveCents = 1200.0) {
   return Math.abs(circleDifference(a, b, equaveCents));
 }
+
+/**
+ * Calculate the smallest power of two greater or equal to the input value.
+ * @param x Value to compare to.
+ * @returns Smallest `2**n` such that `x <= 2**n`.
+ */
+export function ceilPow2(x: number) {
+  if (x >= 1 && x < 0x40000000) {
+    return 1 << (32 - Math.clz32(x - 1));
+  }
+  if (x <= 0) {
+    return 0;
+  }
+  return 2 ** Math.ceil(Math.log2(x));
+}