Implement modInverse for an even modulus.

tests/corelib/big_integer_arith_vm_test.dart

Index: tests/corelib/big_integer_arith_vm_test.dart
diff --git a/tests/corelib/big_integer_arith_vm_test.dart b/tests/corelib/big_integer_arith_vm_test.dart
index 7492d0834e340abea24fb073537de10fce7e43e2..3353756335d7e0ba3cc1354d32d8f5c6ea96b742 100644
--- a/tests/corelib/big_integer_arith_vm_test.dart
+++ b/tests/corelib/big_integer_arith_vm_test.dart
@@ -223,21 +223,14 @@ testBigintModPow() {
   Expect.equals(40128068573873018143207285483, x.modPow(e, m));
 }
 
-// TODO(regis): Remove once even modulus is implemented.
-UnimplementedEvenModulusModInverse(x, m) {
-  Expect.equals(true, m.isEven);
-  try {
-    x.modInverse(m);
-    Expect.fail("Did not throw UnimplementedError");
-  } on UnimplementedError catch (e) {
-  }
-}
-
 testBigintModInverse() {
   var x, m;
+  x = 1;
+  m = 1;
+  Expect.equals(0, x.modInverse(m));
   x = 0;
   m = 1000000001;
-  Expect.equals(0, x.modInverse(m));  // Not coprime.
+  Expect.throws(() => x.modInverse(m), (e) => e is RangeError);  // Not coprime.
   x = 1234567890;
   m = 19;
   Expect.equals(11, x.modInverse(m));
@@ -246,7 +239,7 @@ testBigintModInverse() {
   Expect.equals(189108911, x.modInverse(m));
   x = 19;
   m = 1000000001;
-  Expect.equals(0, x.modInverse(m));  // Not coprime.
+  Expect.throws(() => x.modInverse(m), (e) => e is RangeError);  // Not coprime.
   x = 19;
   m = 1234567890;
   Expect.equals(519818059, x.modInverse(m));
@@ -255,7 +248,7 @@ testBigintModInverse() {
   Expect.equals(1001100101, x.modInverse(m));
   x = 1000000001;
   m = 19;
-  Expect.equals(0, x.modInverse(m));  // Not coprime.
+  Expect.throws(() => x.modInverse(m), (e) => e is RangeError);  // Not coprime.
   x = 12345678901234567890;
   m = 19;
   Expect.equals(3, x.modInverse(m));
@@ -267,10 +260,10 @@ testBigintModInverse() {
   Expect.equals(6315789473684210527, x.modInverse(m));
   x = 19;
   m = 12345678901234567890;
-  UnimplementedEvenModulusModInverse(x, m);
+  Expect.equals(10396361179987004539, x.modInverse(m));
   x = 10000000000000000001;
   m = 12345678901234567890;
-  UnimplementedEvenModulusModInverse(x, m);
+  Expect.equals(325004555487045911, x.modInverse(m));
   x = 10000000000000000001;
   m = 19;
   Expect.equals(7, x.modInverse(m));
@@ -282,7 +275,7 @@ testBigintModInverse() {
   Expect.equals(3, x.modInverse(m));
   x = 123456789012345678901234567890;
   m = 123456789012345678901234567899;
-  Expect.equals(0, x.modInverse(m));  // Not coprime.
+  Expect.throws(() => x.modInverse(m), (e) => e is RangeError);  // Not coprime.
   x = 123456789012345678901234567890;
   m = 123456789012345678901234567891;
   Expect.equals(123456789012345678901234567890, x.modInverse(m));
@@ -291,10 +284,10 @@ testBigintModInverse() {
   Expect.equals(77160493132716049313271604932, x.modInverse(m));
   x = 123456789012345678901234567899;
   m = 123456789012345678901234567890;
-  UnimplementedEvenModulusModInverse(x, m);
+  Expect.throws(() => x.modInverse(m), (e) => e is RangeError);  // Not coprime.
   x = 123456789012345678901234567891;
   m = 123456789012345678901234567890;
-  UnimplementedEvenModulusModInverse(x, m);
+  Expect.equals(1, x.modInverse(m));
   x = 123456789012345678901234567891;
   m = 123456789012345678901234567899;
   Expect.equals(46296295879629629587962962962, x.modInverse(m));