Add more bit manipulation functions.

trekhleb · trekhleb · commit c26820325917 · 2018-06-27T17:33:16.000+03:00
diff --git a/README.md b/README.md
@@ -49,7 +49,7 @@ a set of rules that precisely define a sequence of operations.
 ### Algorithms by Topic
 
 * **Math**
-  * `B` [Bit Manipulation](src/algorithms/math/bits) - set/get/update/clear bits
+  * `B` [Bit Manipulation](src/algorithms/math/bits) - set/get/update/clear bits, multiplication/division by two etc.
   * `B` [Factorial](src/algorithms/math/factorial) 
   * `B` [Fibonacci Number](src/algorithms/math/fibonacci)
   * `B` [Primality Test](src/algorithms/math/primality-test) (trial division method)
diff --git a/src/algorithms/math/bits/README.md b/src/algorithms/math/bits/README.md
@@ -35,3 +35,37 @@ unsets the bit.
 This method is a combination of "Clear Bit" and "Set Bit" methods.
 
 > See `updateBit` function for further details.
+
+#### Multiply By Two
+
+This method shifts original number by one bit to the left.
+Thus all binary number components (powers of two) are being
+multiplying by two and thus the number itself is being 
+multiplied by two.
+
+```
+Before the shift
+Number: 0b0101 = 5
+Powers of two: 0 + 2^2 + 0 + 2^0 
+
+After the shift
+Number: 0b1010 = 10
+Powers of two: 2^3 + 0 + 2^1 + 0 
+```
+
+#### Divide By Two
+
+This method shifts original number by one bit to the right.
+Thus all binary number components (powers of two) are being
+divided by two and thus the number itself is being 
+divided by two without remainder.
+
+```
+Before the shift
+Number: 0b0101 = 5
+Powers of two: 0 + 2^2 + 0 + 2^0 
+
+After the shift
+Number: 0b0010 = 2
+Powers of two: 0 + 0 + 2^1 + 0 
+```
diff --git a/src/algorithms/math/bits/__test__/divideByTwo.test.js b/src/algorithms/math/bits/__test__/divideByTwo.test.js
@@ -0,0 +1,12 @@
+import divideByTwo from '../divideByTwo';
+
+describe('divideByTwo', () => {
+  it('should divide numbers by two using bitwise operations', () => {
+    expect(divideByTwo(0)).toBe(0);
+    expect(divideByTwo(1)).toBe(0);
+    expect(divideByTwo(3)).toBe(1);
+    expect(divideByTwo(10)).toBe(5);
+    expect(divideByTwo(17)).toBe(8);
+    expect(divideByTwo(125)).toBe(62);
+  });
+});
diff --git a/src/algorithms/math/bits/__test__/multiplyByTwo.test.js b/src/algorithms/math/bits/__test__/multiplyByTwo.test.js
@@ -0,0 +1,12 @@
+import multiplyByTwo from '../multiplyByTwo';
+
+describe('multiplyByTwo', () => {
+  it('should multiply numbers by two using bitwise operations', () => {
+    expect(multiplyByTwo(0)).toBe(0);
+    expect(multiplyByTwo(1)).toBe(2);
+    expect(multiplyByTwo(3)).toBe(6);
+    expect(multiplyByTwo(10)).toBe(20);
+    expect(multiplyByTwo(17)).toBe(34);
+    expect(multiplyByTwo(125)).toBe(250);
+  });
+});
diff --git a/src/algorithms/math/bits/divideByTwo.js b/src/algorithms/math/bits/divideByTwo.js
@@ -0,0 +1,7 @@
+/**
+ * @param {number} number
+ * @return {number}
+ */
+export default function divideByTwo(number) {
+  return number >> 1;
+}
diff --git a/src/algorithms/math/bits/multiplyByTwo.js b/src/algorithms/math/bits/multiplyByTwo.js
@@ -0,0 +1,7 @@
+/**
+ * @param {number} number
+ * @return {number}
+ */
+export default function multiplyByTwo(number) {
+  return number << 1;
+}
