Implement Math.random() purely in JavaScript.

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 r;
 }
 
 // ECMA 262 - 15.8.2.13
 function MathPow(x, y) {
   return %_MathPow(TO_NUMBER_INLINE(x), TO_NUMBER_INLINE(y));
 }
 
 // ECMA 262 - 15.8.2.14
+// random0 and random1 are initialized during genesis.
 function MathRandom() {
-  return %_RandomHeapNumber();
+  var r0 = (MathImul(18273, random0 & 0xFFFF) + (random0 >>> 16)) | 0;
+  random0 = r0;

[Michael Starzinger, 2013/11/11 14:11:12]

I am not sure about the sequence of the initialization here. Can we make sure
that "random0" and "random1" are bound to global variables by explicitly
declaring them at the top-level a few lines above? Thereby it is more obvious to
where these two variables are bound.

[Sven Panne, 2013/11/12 07:09:12]

Done.

+  var r1 = (MathImul(36969, random1 & 0xFFFF) + (random1 >>> 16)) | 0;
+  random1 = r1;
+  var x = ((r0 << 14) + (r1 & 0x3FFFF)) | 0;
+  return (x < 0 ? (x + 0x100000000) : x) / 0x100000000;
 }
 
 // ECMA 262 - 15.8.2.15
 function MathRound(x) {
   return %RoundNumber(TO_NUMBER_INLINE(x));
 }
 
 // ECMA 262 - 15.8.2.16
 function MathSin(x) {
   return %_MathSin(TO_NUMBER_INLINE(x));
@@ skipping 83 matching lines @@
     "tan", MathTan,
     "atan2", MathAtan2,
     "pow", MathPow,
     "max", MathMax,
     "min", MathMin,
     "imul", MathImul
   ));
 }
 
 SetUpMath();