Added flag for seeding the random generator deterministically.

Review URL: http://codereview.chromium.org/1247003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4245 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -205,6 +205,9 @@ DEFINE_bool(cleanup_ics_at_gc, true,
             "Flush inline caches prior to mark compact collection.")
 DEFINE_bool(cleanup_caches_in_maps_at_gc, true,
             "Flush code caches in maps during mark compact cycle.")
+DEFINE_int(random_seed, 0,
+           "Default seed for initializing random generator "
+           "(0, the default, means to use system random).")
 
 DEFINE_bool(canonicalize_object_literal_maps, true,
             "Canonicalize maps for object literals.")

src/v8.cc

@@ -155,6 +155,14 @@ void V8::TearDown() {
 }
 
 
+static uint32_t random_seed() {
+  if (FLAG_random_seed == 0) {
+    return random();
+  }
+  return FLAG_random_seed;
+}
+
+
 uint32_t V8::Random() {
   // Random number generator using George Marsaglia's MWC algorithm.
   static uint32_t hi = 0;
@@ -164,8 +172,8 @@ uint32_t V8::Random() {
   // should ever become zero again, or if random() returns zero, we
   // avoid getting stuck with zero bits in hi or lo by re-initializing
   // them on demand.
-  if (hi == 0) hi = random();
-  if (lo == 0) lo = random();
+  if (hi == 0) hi = random_seed();
+  if (lo == 0) lo = random_seed();
 
   // Mix the bits.
   hi = 36969 * (hi & 0xFFFF) + (hi >> 16);