Speed up V8 random number generator, reverting part of 8490.

src/v8.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 83 matching lines @@
 
   if (!has_been_setup_ || has_been_disposed_) return;
   isolate->TearDown();
 
   is_running_ = false;
   has_been_disposed_ = true;
 }
 
 
 static void seed_random(uint32_t* state) {
-  for (int i = 0; i < 4; ++i) {
+  for (int i = 0; i < 2; ++i) {
     state[i] = FLAG_random_seed;
     while (state[i] == 0) {
       state[i] = random();
     }
   }
 }
 
 
 // Random number generator using George Marsaglia's MWC algorithm.
 static uint32_t random_base(uint32_t* state) {
   // Initialize seed using the system random().
   // No non-zero seed will ever become zero again.
   if (state[0] == 0) seed_random(state);
 
   // Mix the bits.  Never replaces state[i] with 0 if it is nonzero.
   state[0] = 18273 * (state[0] & 0xFFFF) + (state[0] >> 16);
   state[1] = 36969 * (state[1] & 0xFFFF) + (state[1] >> 16);
-  state[2] = 23208 * (state[2] & 0xFFFF) + (state[2] >> 16);
-  state[3] = 27753 * (state[3] & 0xFFFF) + (state[3] >> 16);
 
-  return ((state[2] ^ state[3]) << 16) + ((state[0] ^ state[1]) & 0xFFFF);
+  return (state[0] << 14) + (state[1] & 0x3FFFF);
 }
 
 
 // Used by JavaScript APIs
 uint32_t V8::Random(Isolate* isolate) {
   ASSERT(isolate == Isolate::Current());
   return random_base(isolate->random_seed());
 }
 
 
@@ skipping 60 matching lines @@
     use_crankshaft_ = false;
   }
 
   RuntimeProfiler::GlobalSetup();
 
   // Peephole optimization might interfere with deoptimization.
   FLAG_peephole_optimization = !use_crankshaft_;
 }
 
 } }  // namespace v8::internal