Add bits counter function.

Author: trekhleb

src/algorithms/math/bits/README.md

@@ -143,6 +143,19 @@ Count of Bits to be Flipped: 1
 
 > See `bitsDiff` function for further details.
 
+#### Count Bits of a Number
+
+To calculate the number of valuable bits we need to shift `1` one bit left each
+time and see if shifted number is bigger than the input number.
+
+```
+5 = 0b0101
+Count of valuable bits is: 3
+When we shift 1 four times it will become bigger than 5.
+```
+
+> See `bitsDiff` function for further details.
+
 ## References
 
 - [Bit Manipulation on YouTube](https://www.youtube.com/watch?v=NLKQEOgBAnw&t=0s&index=28&list=PLLXdhg_r2hKA7DPDsunoDZ-Z769jWn4R8)

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

@@ -0,0 +1,14 @@
+import bitLength from '../bitLength';
+
+describe('bitLength', () => {
+  it('should calculate number of bits that the number is consists of', () => {
+    expect(bitLength(0b0)).toBe(0);
+    expect(bitLength(0b1)).toBe(1);
+    expect(bitLength(0b01)).toBe(1);
+    expect(bitLength(0b101)).toBe(3);
+    expect(bitLength(0b0101)).toBe(3);
+    expect(bitLength(0b10101)).toBe(5);
+    expect(bitLength(0b11110101)).toBe(8);
+    expect(bitLength(0b00011110101)).toBe(8);
+  });
+});

src/algorithms/math/bits/bitLength.js

@@ -0,0 +1,15 @@
+/**
+ * Return the number of bits used in the binary representation of the number.
+ *
+ * @param {number} number
+ * @return {number}
+ */
+export default function bitLength(number) {
+  let bitsCounter = 0;
+
+  while ((1 << bitsCounter) <= number) {
+    bitsCounter += 1;
+  }
+
+  return bitsCounter;
+}