[#79] Introduce utility function and a class for calculations

api/src/util/calculator.ts

@@ -0,0 +1,70 @@
+import { createHash } from 'crypto';
+
+export function generateMd5Hash(data: string): string {
+  return createHash('md5').update(data).digest('hex');
+}
+
+export class HexaModCalculator {
+  private static hexadecimalDigits: Map<string, number>;
+  private static isInitialized = false;
+
+  private static initialize = () => {
+    HexaModCalculator.hexadecimalDigits = new Map();
+
+    for (let i = 0; i <= 9; i++) {
+      HexaModCalculator.hexadecimalDigits.set(
+        String.fromCharCode(i + '0'.charCodeAt(0)),
+        i
+      );
+    }
+
+    HexaModCalculator.hexadecimalDigits.set('a', 10);
+    HexaModCalculator.hexadecimalDigits.set('b', 11);
+    HexaModCalculator.hexadecimalDigits.set('c', 12);
+    HexaModCalculator.hexadecimalDigits.set('d', 13);
+    HexaModCalculator.hexadecimalDigits.set('e', 14);
+    HexaModCalculator.hexadecimalDigits.set('f', 15);
+  };
+
+  private static ensureInitialize = () => {
+    if (!HexaModCalculator.isInitialized) {
+      HexaModCalculator.initialize();
+      HexaModCalculator.isInitialized = true;
+    }
+  };
+
+  // NOTE: This code is adapted from https://www.geeksforgeeks.org/modulus-of-two-hexadecimal-numbers/
+  public static hexaMod = (hexDividend: string, hexDivisor: string): number => {
+    HexaModCalculator.ensureInitialize();
+
+    const decimalDivisor = parseInt(hexDivisor, 16);
+    if (decimalDivisor <= 0) {
+      throw Error('division by zero is not allowed');
+    }
+
+    let decimalBase = 1;
+    let decimalResult = 0;
+
+    for (let i = hexDividend.length - 1; i >= 0; i--) {
+      const decimalValue = HexaModCalculator.hexadecimalDigits.get(
+        hexDividend[i]
+      );
+      if (decimalValue === undefined) {
+        throw Error('invalid hexadecimal value');
+      }
+
+      const decimalRemainder = decimalValue % decimalDivisor;
+      decimalResult =
+        (decimalResult +
+          ((((decimalBase % decimalDivisor) * decimalRemainder) %
+            decimalDivisor) %
+            decimalDivisor)) %
+        decimalDivisor;
+      decimalBase =
+        (((decimalBase % decimalDivisor) * 16) % decimalDivisor) %
+        decimalDivisor;
+    }
+
+    return decimalResult;
+  };
+}

api/test/util/calculator.test.ts

@@ -0,0 +1,38 @@
+import { HexaModCalculator } from '@src/util/calculator';
+
+describe('Test hexaMod calculator', () => {
+  it('should return correct result', () => {
+    const testSet: Array<[number, number]> = [];
+
+    for (
+      let i = Number.MAX_SAFE_INTEGER - 50;
+      i <= Number.MAX_SAFE_INTEGER;
+      i++
+    ) {
+      testSet.push([i, Math.floor(i / 1000)]);
+    }
+
+    for (const [dividend, divisor] of testSet) {
+      expect(
+        HexaModCalculator.hexaMod(dividend.toString(16), divisor.toString(16))
+      ).toEqual(dividend % divisor);
+    }
+  });
+
+  it('should work correctly even if given dividend is very large', () => {
+    expect(
+      HexaModCalculator.hexaMod(
+        '9ff4599228e14263b7076e2fa7a6477c998fabf315129eee77549ff238bfe26aa9b976f0db9e68f5',
+        '469cbad3'
+      )
+    ).toEqual(114047340);
+  });
+
+  it('should throw Error when given divisor is zero', () => {
+    expect(() => HexaModCalculator.hexaMod('111', '0')).toThrow();
+  });
+
+  it('should throw Error when given dividend is not valid hex', () => {
+    expect(() => HexaModCalculator.hexaMod('xyz', 'ab')).toThrow();
+  });
+});