Implement xorshift128+ for Math.random.

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 79 matching lines @@
     int rnd = Next(31);
     int val = rnd % max;
     if (rnd - val + (max - 1) >= 0) {
       return val;
     }
   }
 }
 
 
 double RandomNumberGenerator::NextDouble() {
-  return ((static_cast<int64_t>(Next(26)) << 27) + Next(27)) /
-      static_cast<double>(static_cast<int64_t>(1) << 53);
+  XorShift128(&state0_, &state1_);
+  return ToDouble(state0_, state1_);
 }
 
 
 int64_t RandomNumberGenerator::NextInt64() {
-  uint64_t lo = bit_cast<unsigned>(Next(32));
-  uint64_t hi = bit_cast<unsigned>(Next(32));
-  return lo | (hi << 32);
+  XorShift128(&state0_, &state1_);
+  return bit_cast<int64_t>(state0_ + state1_);
 }
 
 
 void RandomNumberGenerator::NextBytes(void* buffer, size_t buflen) {
   for (size_t n = 0; n < buflen; ++n) {
     static_cast<uint8_t*>(buffer)[n] = static_cast<uint8_t>(Next(8));
   }
 }
 
 
 int RandomNumberGenerator::Next(int bits) {
   DCHECK_LT(0, bits);
   DCHECK_GE(32, bits);
-  // Do unsigned multiplication, which has the intended modulo semantics, while
-  // signed multiplication would expose undefined behavior.
-  uint64_t product = static_cast<uint64_t>(seed_) * kMultiplier;
-  // Assigning a uint64_t to an int64_t is implementation defined, but this
-  // should be OK. Use a static_cast to explicitly state that we know what we're
-  // doing. (Famous last words...)
-  int64_t seed = static_cast<int64_t>((product + kAddend) & kMask);
-  seed_ = seed;
-  return static_cast<int>(seed >> (48 - bits));
+  XorShift128(&state0_, &state1_);
+  return static_cast<int>((state0_ + state1_) >> (64 - bits));
 }
 
 
 void RandomNumberGenerator::SetSeed(int64_t seed) {
   initial_seed_ = seed;
-  seed_ = (seed ^ kMultiplier) & kMask;
+  state0_ = MurmurHash3(bit_cast<uint64_t>(seed));
+  state1_ = MurmurHash3(state0_);
+}
+
+
+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