[rng] improve RNG seed.

src/base/utils/random-number-generator.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/utils/random-number-generator.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 
 #include <new>
@@ skipping 106 matching lines @@
 
 int RandomNumberGenerator::Next(int bits) {
   DCHECK_LT(0, bits);
   DCHECK_GE(32, bits);
   XorShift128(&state0_, &state1_);
   return static_cast<int>((state0_ + state1_) >> (64 - bits));
 }
 
 
 void RandomNumberGenerator::SetSeed(int64_t seed) {
-  if (seed == 0) seed = 1;
   initial_seed_ = seed;
   state0_ = MurmurHash3(bit_cast<uint64_t>(seed));
-  state1_ = MurmurHash3(state0_);
+  state1_ = MurmurHash3(~state0_);
+  CHECK(state0_ != 0 || state1_ != 0);
 }
 
 
 uint64_t RandomNumberGenerator::MurmurHash3(uint64_t h) {
   h ^= h >> 33;
   h *= V8_UINT64_C(0xFF51AFD7ED558CCD);
   h ^= h >> 33;
   h *= V8_UINT64_C(0xC4CEB9FE1A85EC53);
   h ^= h >> 33;
   return h;
 }
 
 }  // namespace base
 }  // namespace v8