Fix http://dartbug.com/16111

runtime/lib/math.cc

 // Copyright (c) 2011, 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.
 
 #include <ctype.h>  // isspace.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/exceptions.h"
@@ skipping 105 matching lines @@
 //     seed = (seed + 0x5A17) & _Random._MASK_64;
 //   } while (seed == 0);
 //   _state[kSTATE_LO] = seed & _MASK_32;
 //   _state[kSTATE_HI] = seed >> 32;
 DEFINE_NATIVE_ENTRY(Random_setupSeed, 2) {
   GET_NON_NULL_NATIVE_ARGUMENT(Instance, receiver, arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Integer, seed_int, arguments->NativeArgAt(1));
   const TypedData& array = TypedData::Handle(GetRandomStateArray(receiver));
   ASSERT(!seed_int.IsNull());
   ASSERT(!array.IsNull());
-  // TODO(srdjan): Reduce Bigint to 64 bit value.
-  int64_t seed = seed_int.IsBigint() ? 0 : seed_int.AsInt64Value();
+  int64_t seed = 0;
+  if (seed_int.IsBigint()) {
+    const Bigint& mask64 = Bigint::Handle(
+        BigintOperations::NewFromUint64(0xffffffffffffffff));
+    Bigint& big_seed = Bigint::Handle();
+    big_seed ^= seed_int.raw();
+    Bigint& low64 = Bigint::Handle();
+    while (!big_seed.IsZero()) {
+      low64 = BigintOperations::BitAnd(big_seed, mask64);
+      ASSERT(BigintOperations::FitsIntoUint64(low64));
+      seed ^= BigintOperations::ToUint64(low64);
+      big_seed = BigintOperations::ShiftRight(big_seed, 64);
+    }
+  } else {
+    seed = seed_int.AsInt64Value();
+  }
+
   do {
     seed = seed + 0x5A17;
   } while (seed == 0);
   array.SetUint32(0, static_cast<uint32_t>(seed));
   array.SetUint32(array.ElementSizeInBytes(),
       static_cast<uint32_t>(seed >> 32));
   return Object::null();
 }
 
 }  // namespace dart