Use Marsaglia's original random number generator.

src/math.js

 // Copyright 2012 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 156 matching lines @@
   return %_MathPow(TO_NUMBER_INLINE(x), TO_NUMBER_INLINE(y));
 }
 
 // ECMA 262 - 15.8.2.14
 var rngstate;  // Initialized to a Uint32Array during genesis.
 function MathRandom() {
   var r0 = (MathImul(18273, rngstate[0] & 0xFFFF) + (rngstate[0] >>> 16)) | 0;
   rngstate[0] = r0;
   var r1 = (MathImul(36969, rngstate[1] & 0xFFFF) + (rngstate[1] >>> 16)) | 0;
   rngstate[1] = r1;
-  var x = ((r0 << 14) + (r1 & 0x3FFFF)) | 0;
+  var x = ((r0 << 16) + (r1 & 0xFFFF)) | 0;
   // Division by 0x100000000 through multiplication by reciprocal.
   return (x < 0 ? (x + 0x100000000) : x) * 2.3283064365386962890625e-10;
 }
 
 // ECMA 262 - 15.8.2.15
 function MathRound(x) {
   return %RoundNumber(TO_NUMBER_INLINE(x));
 }
 
 // ECMA 262 - 15.8.2.16
@@ skipping 202 matching lines @@
     "min", MathMin,
     "imul", MathImul
   ));
 
   %SetInlineBuiltinFlag(MathSin);
   %SetInlineBuiltinFlag(MathCos);
   %SetInlineBuiltinFlag(MathTan);
 }
 
 SetUpMath();