- Avoid exposing the 64-bit state of the PRNG to Dart code.

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 93 matching lines @@
   const uint64_t state_hi = array.GetUint32(array.ElementSizeInBytes());
   const uint64_t A = 0xffffda61;
   uint64_t state = (A * state_lo) + state_hi;
   array.SetUint32(0, static_cast<uint32_t>(state));
   array.SetUint32(array.ElementSizeInBytes(),
       static_cast<uint32_t>(state >> 32));
   return Object::null();
 }
 
 
+RawTypedData* CreateRandomState(Isolate* isolate, uint64_t seed) {
+  const TypedData& result = TypedData::Handle(
+      isolate, TypedData::New(kTypedDataUint32ArrayCid, 2));
+  result.SetUint32(0, static_cast<uint32_t>(seed));
+  result.SetUint32(result.ElementSizeInBytes(),
+                   static_cast<uint32_t>(seed >> 32));
+  return result.raw();
+}
+
+
 uint64_t mix64(uint64_t n) {
   // Thomas Wang 64-bit mix.
   // http://www.concentric.net/~Ttwang/tech/inthash.htm
   // via. http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm
   n = (~n) + (n << 21);           // n = (n << 21) - n - 1;
   n = n ^ (n >> 24);
   n = n * 265;                    // n = (n + (n << 3)) + (n << 8);
   n = n ^ (n >> 14);
   n = n * 21;                     // n = (n + (n << 2)) + (n << 4);
   n = n ^ (n >> 28);
   n = n + (n << 31);
   return n;
 }
 
 
 // Implements:
 //   uint64_t hash = 0;
 //   do {
 //      hash = hash * 1037 ^ mix64((uint64_t)seed);
 //      seed >>= 64;
 //   } while (seed != 0 && seed != -1);  // Limits if seed positive or negative.
 //   if (hash == 0) {
 //     hash = 0x5A17;
 //   }
-//   _state[kSTATE_LO] = hash & _MASK_32;
-//   _state[kSTATE_HI] = hash >> 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());
+//   var result = new Uint32List(2);
+//   result[kSTATE_LO] = seed & _MASK_32;
+//   result[kSTATE_HI] = seed >> 32;
+//   return result;
+DEFINE_NATIVE_ENTRY(Random_setupSeed, 1) {
+  GET_NON_NULL_NATIVE_ARGUMENT(Integer, seed_int, arguments->NativeArgAt(0));
   uint64_t seed = 0;
   if (seed_int.IsBigint()) {
     const Bigint& mask64 = Bigint::Handle(
         BigintOperations::NewFromUint64(0xffffffffffffffffLL));
     Bigint& big_seed = Bigint::Handle();
     big_seed ^= seed_int.raw();
     uint64_t negate_mask = 0;
     if (big_seed.IsNegative()) {
       // Negate bits to make seed positive.
       // Negate bits again (by xor with negate_mask) when extracted below,
       // to get original bits.
       negate_mask = 0xffffffffffffffffLL;
       big_seed ^= BigintOperations::BitNot(big_seed);
     }
     Bigint& low64 = Bigint::Handle();
     do {
       low64 = BigintOperations::BitAnd(big_seed, mask64);
       ASSERT(BigintOperations::FitsIntoUint64(low64));
       uint64_t chunk = BigintOperations::ToUint64(low64) ^ negate_mask;
       seed = (seed * 1037) ^ mix64(chunk);
       big_seed = BigintOperations::ShiftRight(big_seed, 64);
     } while (!big_seed.IsZero());
   } else {
     seed = mix64(static_cast<uint64_t>(seed_int.AsInt64Value()));
   }
 
   if (seed == 0) {
     seed = 0x5a17;
   }
-  array.SetUint32(0, static_cast<uint32_t>(seed));
-  array.SetUint32(array.ElementSizeInBytes(),
-      static_cast<uint32_t>(seed >> 32));
-  return Object::null();
+  return CreateRandomState(isolate, seed);
 }
 
 
 DEFINE_NATIVE_ENTRY(Random_initialSeed, 0) {
   Random* rnd = isolate->random();
-  int64_t seed = rnd->NextUInt32();
-  seed |= (static_cast<int64_t>(rnd->NextUInt32())) << 32;
-  return Integer::New(seed);
+  uint64_t seed = rnd->NextUInt32();
+  seed |= (static_cast<uint64_t>(rnd->NextUInt32())) << 32;

[siva, 2014/03/17 21:19:04]

I would write this as :

seed |= (static_cast<uint64_t>(rnd->NextUint32()) << 32);

+  return CreateRandomState(isolate, seed);
 }
 
 }  // namespace dart