Implement xorshift128+ for Math.random.

src/js/math.js

Index: src/js/math.js
diff --git a/src/js/math.js b/src/js/math.js
index 18ea596408c6dc63754097a34008f52cdcf20b84..38d4334d9ec95489c586dab64ac46e3a874e7c85 100644
--- a/src/js/math.js
+++ b/src/js/math.js
@@ -10,18 +10,18 @@
 // -------------------------------------------------------------------
 // Imports
 
+define kRandomBatchSize = 64;
+define kRandomNumberStart = 2;

[Jakob Kummerow, 2015/11/23 14:34:08]

nit: maybe add a comment here that indices 0 and 1 are used to store the RNG's
state?

+
+var GlobalFloat64Array = global.Float64Array;
 var GlobalMath = global.Math;
 var GlobalObject = global.Object;
 var InternalArray = utils.InternalArray;
 var NaN = %GetRootNaN();
-var rngstate = { a: 1, b: 2, c: 3, d: 4 };
+var nextRandomIndex = kRandomBatchSize;
+var randomNumbers = UNDEFINED;
 var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
 
-utils.InitializeRNG = function() {
-  var state = %InitializeRNG();
-  rngstate = { a: state[0], b: state[1], c: state[2], d: state[3] };
-};
-
 //-------------------------------------------------------------------
 
 // ECMA 262 - 15.8.2.1
@@ -135,26 +135,19 @@ function MathPowJS(x, y) {
 
 // ECMA 262 - 15.8.2.14
 function MathRandom() {
-  var r0 = (MathImul(18030, rngstate.a) + rngstate.b) | 0;
-  var r1 = (MathImul(36969, rngstate.c) + rngstate.d) | 0;
-  rngstate.a = r0 & 0xFFFF;
-  rngstate.b = r0 >>> 16;
-  rngstate.c = r1 & 0xFFFF;
-  rngstate.d = r1 >>> 16;
-  var r = r0 ^ r1;
-  // Construct a double number 1.<32-bits of randomness> and subtract 1.
-  return %_ConstructDouble(0x3FF00000 | (r & 0x000FFFFF), r & 0xFFF00000) - 1;
+  if (nextRandomIndex >= kRandomBatchSize) {
+    randomNumbers = %GenerateRandomNumbers(randomNumbers);
+    nextRandomIndex = kRandomNumberStart;
+  }
+  return randomNumbers[nextRandomIndex++];
 }
 
 function MathRandomRaw() {
-  var r0 = (MathImul(18030, rngstate.a) + rngstate.b) | 0;
-  var r1 = (MathImul(36969, rngstate.c) + rngstate.d) | 0;
-  rngstate.a = r0 & 0xFFFF;
-  rngstate.b = r0 >>> 16;
-  rngstate.c = r1 & 0xFFFF;
-  rngstate.d = r1 >>> 16;
-  var r = r0 ^ r1;
-  return r & 0x3FFFFFFF;
+  if (nextRandomIndex >= kRandomBatchSize) {
+    randomNumbers = %GenerateRandomNumbers(randomNumbers);
+    nextRandomIndex = kRandomNumberStart;
+  }
+  return %_DoubleLo(randomNumbers[nextRandomIndex++]) & 0x3FFFFFFF;
 }
 
 // ECMA 262 - 15.8.2.15
@@ -354,7 +347,7 @@ utils.Export(function(to) {
   to.MathAbs = MathAbs;
   to.MathExp = MathExp;
   to.MathFloor = MathFloorJS;
-  to.IntRandom = MathRandomRaw;
+  to.MathRandomRaw = MathRandomRaw;
   to.MathMax = MathMax;
   to.MathMin = MathMin;
 });