Revert of Implement xorshift128+ for Math.random.

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

Index: src/base/utils/random-number-generator.h
diff --git a/src/base/utils/random-number-generator.h b/src/base/utils/random-number-generator.h
index cd3e6bfdc89906d00e80340174fdb52865bbcfa9..10f2789c7dffea7334051f58cc40a80edbf822e3 100644
--- a/src/base/utils/random-number-generator.h
+++ b/src/base/utils/random-number-generator.h
@@ -12,16 +12,10 @@
 
 // -----------------------------------------------------------------------------
 // RandomNumberGenerator
-
-// This class is used to generate a stream of pseudo-random numbers. The class
-// uses a 64-bit seed, which is passed through MurmurHash3 to create two 64-bit
-// state values. This pair of state values is then used in xorshift128+.
-// The resulting stream of pseudo-random numbers has a period length of 2^128-1.
-// See Marsaglia: http://www.jstatsoft.org/v08/i14/paper
-// And Vigna: http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
-// NOTE: Any changes to the algorithm must be tested against TestU01.
-//       Please find instructions for this in the internal repository.
-
+//
+// This class is used to generate a stream of pseudorandom numbers. The class
+// uses a 48-bit seed, which is modified using a linear congruential formula.
+// (See Donald Knuth, The Art of Computer Programming, Volume 3, Section 3.2.1.)
 // If two instances of RandomNumberGenerator are created with the same seed, and
 // the same sequence of method calls is made for each, they will generate and
 // return identical sequences of numbers.
@@ -89,27 +83,6 @@
 
   int64_t initial_seed() const { return initial_seed_; }
 
-  // Static and exposed for external use.
-  static inline double ToDouble(uint64_t state0, uint64_t state1) {
-    // Exponent for double values for [1.0 .. 2.0)
-    static const uint64_t kExponentBits = V8_UINT64_C(0x3FF0000000000000);
-    static const uint64_t kMantissaMask = V8_UINT64_C(0x000FFFFFFFFFFFFF);
-    uint64_t random = ((state0 + state1) & kMantissaMask) | kExponentBits;
-    return bit_cast<double>(random) - 1;
-  }
-
-  // Static and exposed for external use.
-  static inline void XorShift128(uint64_t* state0, uint64_t* state1) {
-    uint64_t s1 = *state0;
-    uint64_t s0 = *state1;
-    *state0 = s0;
-    s1 ^= s1 << 23;
-    s1 ^= s1 >> 17;
-    s1 ^= s0;
-    s1 ^= s0 >> 26;
-    *state1 = s1;
-  }
-
  private:
   static const int64_t kMultiplier = V8_2PART_UINT64_C(0x5, deece66d);
   static const int64_t kAddend = 0xb;
@@ -117,11 +90,8 @@
 
   int Next(int bits) WARN_UNUSED_RESULT;
 
-  static uint64_t MurmurHash3(uint64_t);
-
   int64_t initial_seed_;
-  uint64_t state0_;
-  uint64_t state1_;
+  int64_t seed_;
 };
 
 }  // namespace base