Replace fraction addition implementation with a 1% faster version

package.json

@@ -48,7 +48,9 @@
     "premonzo-benchmark": "tsc -p tsconfig-benchmark.json",
     "monzo-benchmark": "node benchmarks/__benchmarks__/monzo.mark.js",
     "preprimes-benchmark": "tsc -p tsconfig-benchmark.json",
-    "primes-benchmark": "node benchmarks/__benchmarks__/primes.mark.js"
+    "primes-benchmark": "node benchmarks/__benchmarks__/primes.mark.js",
+    "prefraction-benchmark": "tsc -p tsconfig-benchmark.json",
+    "fraction-benchmark": "node benchmarks/__benchmarks__/fraction.mark.js"
   },
   "engines": {
     "node": ">=10.6.0"

src/__benchmarks__/fraction.mark.ts

@@ -0,0 +1,48 @@
+// @ts-ignore
+import Benchmark = require('benchmark');
+import {Fraction, gcd, lcm} from '..';
+
+function addWithLcm(self: Fraction, other: Fraction) {
+  const {s, n, d} = new Fraction(other);
+  const denominator = lcm(self.d, d);
+  return new Fraction(
+    self.s * self.n * (denominator / self.d) + s * n * (denominator / d),
+    denominator
+  );
+}
+
+function addWithGcd(self: Fraction, other: Fraction) {
+  const {s, n, d} = new Fraction(other);
+  const factor = gcd(self.d, d);
+  const df = d / factor;
+  return new Fraction(
+    self.s * self.n * df + s * n * (self.d / factor),
+    df * self.d
+  );
+}
+
+function randomFraction() {
+  return new Fraction(
+    Math.floor(Math.random() * 10000),
+    Math.floor(Math.random() * 10000) + 1
+  );
+}
+
+const fractionAddSuite = new Benchmark.Suite();
+fractionAddSuite
+  .add('current implementation', () => {
+    randomFraction().add(randomFraction());
+  })
+  .add('old implementation (using lcm)', () => {
+    addWithLcm(randomFraction(), randomFraction());
+  })
+  .add('new implementation (using gcd)', () => {
+    addWithGcd(randomFraction(), randomFraction());
+  })
+  .on('cycle', (event: {target: any}) => {
+    console.log(String(event.target));
+  })
+  .on('complete', () => {
+    console.log('Fastest is ' + fractionAddSuite.filter('fastest').map('name'));
+  })
+  .run({async: true});

src/fraction.ts

@@ -481,10 +481,11 @@ export class Fraction {
   add(other: FractionValue) {
     const {s, n, d} = new Fraction(other);
     // Must pre-reduce to avoid blowing the limits
-    const denominator = lcm(this.d, d);
+    const factor = gcd(this.d, d);
+    const df = d / factor;
     return new Fraction(
-      this.s * this.n * (denominator / this.d) + s * n * (denominator / d),
-      denominator
+      this.s * this.n * df + s * n * (this.d / factor),
+      df * this.d
     );
   }
 
@@ -496,10 +497,11 @@ export class Fraction {
   sub(other: FractionValue) {
     const {s, n, d} = new Fraction(other);
     // Must pre-reduce to avoid blowing the limits
-    const denominator = lcm(this.d, d);
+    const factor = gcd(this.d, d);
+    const df = d / factor;
     return new Fraction(
-      this.s * this.n * (denominator / this.d) - s * n * (denominator / d),
-      denominator
+      this.s * this.n * df - s * n * (this.d / factor),
+      df * this.d
     );
   }