Revert of Implement xorshift128+ for Math.random.

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

Index: src/base/utils/random-number-generator.cc
diff --git a/src/base/utils/random-number-generator.cc b/src/base/utils/random-number-generator.cc
index 53a37526714a127f8ad9bf68677e7d88eaae6496..4cf06a90473096d0101913cfdf788298db91f618 100644
--- a/src/base/utils/random-number-generator.cc
+++ b/src/base/utils/random-number-generator.cc
@@ -97,14 +97,15 @@
 
 
 double RandomNumberGenerator::NextDouble() {
-  XorShift128(&state0_, &state1_);
-  return ToDouble(state0_, state1_);
+  return ((static_cast<int64_t>(Next(26)) << 27) + Next(27)) /
+      static_cast<double>(static_cast<int64_t>(1) << 53);
 }
 
 
 int64_t RandomNumberGenerator::NextInt64() {
-  XorShift128(&state0_, &state1_);
-  return bit_cast<int64_t>(state0_ + state1_);
+  uint64_t lo = bit_cast<unsigned>(Next(32));
+  uint64_t hi = bit_cast<unsigned>(Next(32));
+  return lo | (hi << 32);
 }
 
 
@@ -118,25 +119,21 @@
 int RandomNumberGenerator::Next(int bits) {
   DCHECK_LT(0, bits);
   DCHECK_GE(32, bits);
-  XorShift128(&state0_, &state1_);
-  return static_cast<int>((state0_ + state1_) >> (64 - 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));
 }
 
 
 void RandomNumberGenerator::SetSeed(int64_t seed) {
   initial_seed_ = seed;
-  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;
+  seed_ = (seed ^ kMultiplier) & kMask;
 }
 
 }  // namespace base