Implement math.gcd in dart.

pkg/math/test/gcd_test.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library math_test;
+import "package:expect/expect.dart";
+import 'dart:math';
+import 'package:math/math.dart';
+
+void testGcd() {
+  Expect.equals(7, gcd(0, 7));
+  Expect.equals(5, gcd(5, 0));
+  Expect.equals(5, gcd(-5, 0));
+  Expect.equals(0, gcd(0, 0));
+  Expect.equals(1, gcd(5, 7));
+  Expect.equals(6, gcd(12, 18));
+  Expect.equals(6, gcd(12, -18));
+  Expect.equals(6, gcd(-12, -18));
+  Expect.equals(6, gcd(18, 12));
+  Expect.equals(15, gcd(45, 105));
+
+  Expect.throws(() => gcd(0, null), (e) => e is ArgumentError);
+  Expect.throws(() => gcd(null, 0), (e) => e is ArgumentError);
+
+  // Cover all branches in Binary GCD implementation.
+  // 0 shared powers-of-two factors.
+  Expect.equals(1, gcd(2*2, 7));
+  // 1 shared power-of-two factor.
+  Expect.equals(2, gcd(2*2, 2*7));
+  // >1 shared powers-of-two factors.
+  Expect.equals(8, gcd(2*2*2*3, 2*2*2*5));
+
+  // 0 remaining powers-of-two in a.
+  Expect.equals(6, gcd(2*3, 2*3*3));
+  // 1 remaining power-of-two in a.
+  Expect.equals(6, gcd(2*2*3, 2*3*3));
+  // >1 remaining powers-of-two in a.
+  Expect.equals(6, gcd(2*2*2*2*3, 2*3*3));
+
+  // 0 remaining powers-of-two in b.
+  Expect.equals(6, gcd(2*3, 2*3*3));
+  // 1 remaining power-of-two in b.
+  Expect.equals(6, gcd(2*3, 2*2*3));
+  // >1 remaining powers-of-two in b.
+  Expect.equals(6, gcd(2*3, 2*2*2*3*3));
+
+  // Innermost 'if'
+  // a > b.
+  Expect.equals(6, gcd(2*2*3*5, 2*3));
+  // a == b.
+  Expect.equals(6, gcd(2*3, 2*2*2*3));
+  // a < b.
+  Expect.equals(6, gcd(2*3, 2*2*3*7));
+
+  // do while loop executions.
+  // Executed 1 time.
+  Expect.equals(6, gcd(2*3, 2*2*2*3));
+  // Executed >1 times.
+  Expect.equals(6, gcd(2*3*3, 2*2*3*5));
+
+  // Medium int (mint) arguments.
+  Expect.equals(pow(2, 61), gcd(pow(2, 61)*3, pow(2,62)));
+  // 9079837958533 is the first prime after 2**48 / 31.
+  Expect.equals(9079837958533,
+    gcd(31*9079837958533, 37*9079837958533));
+}
+
+main() {
+  testGcd();
+}