fix: validate values passed to isPowerOfTwo()

packages/melonjs/CHANGELOG.md

@@ -23,6 +23,7 @@
 - UI: `UITextButton#bitmapText`, for `label`
 
 ### Fixed
+- Math: `isPowerOfTwo()` rejects zero, negative and fractional values instead of accepting them after 32-bit coercion, and handles powers and non-powers beyond the 32-bit range (thanks @mmporong)
 - Input: a child cropped out of view by a container with `clipping`, or scrolled out of a `UIPanel`, no longer gets pointer events where it is not drawn
 - UI: a `UITextButton` moved after it was built draws its background where it is, not where it was first put
 - UI: a blocking `UIPanel` stays opaque to hover for as long as the pointer is on it, not only on the frame the pointer enters

packages/melonjs/src/math/math.ts

@@ -34,7 +34,11 @@ export const EPSILON = 0.000001;
  * @returns true if number is a power of two
  */
 export function isPowerOfTwo(val: number) {
-	return (val & (val - 1)) === 0;
+	if (!Number.isInteger(val) || val <= 0) {
+		return false;
+	}
+	const exponent = Math.log2(val);
+	return Number.isInteger(exponent) && val === 2 ** exponent;
 }
 
 /**

packages/melonjs/tests/math.spec.js

@@ -328,6 +328,27 @@ describe("Math", () => {
 		it("32 is a Power of 2", () => {
 			expect(math.isPowerOfTwo(32)).toEqual(true);
 		});
+		it("0 and negative values are not Powers of 2", () => {
+			expect(math.isPowerOfTwo(0)).toEqual(false);
+			expect(math.isPowerOfTwo(-2)).toEqual(false);
+		});
+		it("fractional values are not Powers of 2", () => {
+			expect(math.isPowerOfTwo(2.5)).toEqual(false);
+		});
+		it("supports Powers of 2 outside the 32-bit range", () => {
+			expect(math.isPowerOfTwo(2 ** 40)).toEqual(true);
+			expect(math.isPowerOfTwo(3 * 2 ** 32)).toEqual(false);
+		});
+		it("rejects large non-Powers whose logarithms round to integers", () => {
+			for (const value of [
+				Number.MAX_SAFE_INTEGER,
+				2 ** 53 + 2,
+				2 ** 53 + 4,
+				2 ** 54 - 2,
+			]) {
+				expect(math.isPowerOfTwo(value)).toEqual(false);
+			}
+		});
 		it("1027 is not a Power of 2", () => {
 			expect(math.isPowerOfTwo(1027)).toEqual(false);
 		});