build: remove next-pow-2 dependency (#21)

This is such a small function that it's not worth having an external dependency.

package.json

@@ -46,8 +46,7 @@
   },
   "homepage": "https://github.com/ianprime0509/pitchy#readme",
   "dependencies": {
-    "fft.js": "^4.0.4",
-    "next-pow-2": "^1.0.0"
+    "fft.js": "^4.0.4"
   },
   "devDependencies": {
     "@types/jest": "^27.0.3",

src/index.ts

@@ -1,5 +1,6 @@
 import FFT from "fft.js";
-import np2 from "next-pow-2";
+
+import { ceilPow2 } from "./util";
 
 /**
  * One of the supported buffer types. Other numeric array types may not work
@@ -85,7 +86,7 @@ export class Autocorrelator<T extends Buffer> {
     this._inputLength = inputLength;
     // We need to double the input length to get correct results, and the FFT
     // algorithm we use requires a length that's a power of 2
-    this._fft = new FFT(np2(2 * inputLength));
+    this._fft = new FFT(ceilPow2(2 * inputLength));
     this._bufferSupplier = bufferSupplier;
     this._paddedInputBuffer = this._bufferSupplier(this._fft.size);
     this._transformBuffer = this._bufferSupplier(2 * this._fft.size);

src/util.test.ts

@@ -0,0 +1,11 @@
+/* eslint-env jest */
+import { ceilPow2 } from "./util";
+
+describe("ceilPow2", () => {
+  test("returns the next power of 2 at least as large as the input", () => {
+    expect(ceilPow2(1)).toBe(1);
+    expect(ceilPow2(2)).toBe(2);
+    expect(ceilPow2(5)).toBe(8);
+    expect(ceilPow2(255)).toBe(256);
+  });
+});

src/util.ts

@@ -0,0 +1,11 @@
+export function ceilPow2(v: number): number {
+  // https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+  v--;
+  v |= v >> 1;
+  v |= v >> 2;
+  v |= v >> 4;
+  v |= v >> 8;
+  v |= v >> 16;
+  v++;
+  return v;
+}

vite.config.ts

@@ -10,11 +10,10 @@ export default defineConfig({
     },
     sourcemap: true,
     rollupOptions: {
-      external: ["fft.js", "next-pow-2"],
+      external: ["fft.js"],
       output: {
         globals: {
           "fft.js": "fft",
-          "next-pow-2": "np2",
         },
       },
     },