Add isPowerOfTwo function.

Author: trekhleb

src/algorithms/math/bits/README.md

@@ -91,23 +91,6 @@ inverting all of the bits of the number and adding 1 to it.
 
 > See [switchSign.js](switchSign.js) for further details.
 
-#### Power of 2
-
-This method checks if a number provided is power of two. It uses the property that when
-a power of 2 is `&` with power of 2 minus 1, it would return 0 implying that the provided
-number is power of 2.
-
-```
-Number: 4
-Power of 2: True
-
-Number: 1
-Power of 2: False
-```
-
-> See `ifPowerof2` function for further details.
-
-
 #### Multiply Two Numbers
 
 This method multiplies two integer numbers using bitwise operators.
@@ -173,6 +156,24 @@ When we shift 1 four times it will become bigger than 5.
 
 > See [bitLength.js](bitLength.js) for further details.
 
+#### Is Power of Two
+
+This method checks if a number provided is power of two. It uses the following 
+property. Let's say that `powerNumber` is a number that has been formed as a power
+of two (i.e. 2, 4, 8, 16 etc.). Then if we'll do `&` operation between `powerNumber`
+and `powerNumber - 1` it will return `0` (in case if number is power of two).
+
+```
+Number: 4 = 0b0100
+Number: 3 = (4 - 1) = 0b0011
+4 & 3 = 0b0100 & 0b0011 = 0b0000 <-- Equal to zero, is power of two.
+
+Number: 10 = 0b01010
+Number: 9 = (10 - 1) = 0b01001
+10 & 9 = 0b01010 & 0b01001 = 0b01000 <-- Not equal to zero, not a power of two.
+```
+
+> See [isPowerOfTwo.js](isPowerOfTwo.js) for further details.
 
 ## References
 

src/algorithms/math/bits/__test__/ifPowerOf2.test.js

@@ -0,0 +1,20 @@
+import isPowerOfTwo from '../isPowerOfTwo';
+
+describe('isPowerOfTwo', () => {
+  it('should detect if the number is power of two', () => {
+    expect(isPowerOfTwo(1)).toBe(true);
+    expect(isPowerOfTwo(2)).toBe(true);
+    expect(isPowerOfTwo(3)).toBe(false);
+    expect(isPowerOfTwo(4)).toBe(true);
+    expect(isPowerOfTwo(5)).toBe(false);
+    expect(isPowerOfTwo(6)).toBe(false);
+    expect(isPowerOfTwo(7)).toBe(false);
+    expect(isPowerOfTwo(8)).toBe(true);
+    expect(isPowerOfTwo(9)).toBe(false);
+    expect(isPowerOfTwo(16)).toBe(true);
+    expect(isPowerOfTwo(23)).toBe(false);
+    expect(isPowerOfTwo(32)).toBe(true);
+    expect(isPowerOfTwo(127)).toBe(false);
+    expect(isPowerOfTwo(128)).toBe(true);
+  });
+});

src/algorithms/math/bits/__test__/isPowerOfTwo.test.js

@@ -0,0 +1,7 @@
+/**
+ * @param {number} number
+ * @return bool
+ */
+export default function isPowerOfTwo(number) {
+  return (number & (number - 1)) === 0;
+}