Changeset 40968 in webkit for trunk/JavaScriptCore/wtf

Timestamp:

Feb 13, 2009, 1:18:43 AM (16 years ago)

Author:

[email protected]

Message:

Math.random is really slow on windows.

Reviewed by Jon Honeycutt.

Math.random calls WTF::randomNumber which is implemented as
the secure rand_s on windows. Unfortunately rand_s is an order
of magnitude slower than arc4random. For this reason I've
added "weakRandomNumber" for use by JavaScript's Math Object.
In the long term we should look at using our own secure PRNG
in place of the system, but this will do for now.

30% win on SunSpider on Windows, resolving most of the remaining
disparity vs. Mac.

Location:

trunk/JavaScriptCore/wtf

Files:

• RandomNumber.cpp (modified) (1 diff)
• RandomNumber.h (modified) (1 diff)
• RandomNumberSeed.h (modified) (1 diff)

trunk/JavaScriptCore/wtf/RandomNumber.cpp

@@ -36 +36 @@
 
 namespace WTF {
+
+double weakRandomNumber()
+{
+#if COMPILER(MSVC) && defined(_CRT_RAND_S)
+    // rand_s is incredibly slow on windows so we fall back on rand for Math.random
+    return (rand() + (rand() / (RAND_MAX + 1.0))) / (RAND_MAX + 1.0);
+#else
+    return randomNumber();
+#endif
+}
 
 double randomNumber()

trunk/JavaScriptCore/wtf/RandomNumber.h

@@ -29 +29 @@
 namespace WTF {
 
-    // Returns a pseudo-random number in the range [0, 1)
+    // Returns a pseudo-random number in the range [0, 1), attempts to be
+    // cryptographically secure if possible on the target platform
     double randomNumber();
+
+    // Returns a pseudo-random number in the range [0, 1), attempts to
+    // produce a reasonable "random" number fast.
+    // We only need this because rand_s is so slow on windows.
+    double weakRandomNumber();
 
 }

trunk/JavaScriptCore/wtf/RandomNumberSeed.h

@@ -58 +58 @@
 }
 
+inline void initializeWeakRandomNumberGenerator()
+{
+#if COMPILER(MSVC) && defined(_CRT_RAND_S)
+    // We need to initialise windows rand() explicitly for Math.random
+    unsigned seed = 0;
+    rand_s(&seed);
+    srand(seed);
+#endif
+}
 }