base: Use the global Mersenne twister throughout

This patch tidies up random number generation to ensure that it is
done consistently throughout the code base. In essence this involves a
clean-up of Ruby, and some code simplifications in the traffic
generator.

As part of this patch a bunch of skewed distributions (off-by-one etc)
have been fixed.

Note that a single global random number generator is used, and that
the object instantiation order will impact the behaviour (the sequence
of numbers will be unaffected, but if module A calles random before
module B then they would obviously see a different outcome). The
dependency on the instantiation order is true in any case due to the
execution-model of gem5, so we leave it as is. Also note that the
global ranom generator is not thread safe at this point.

Regressions using the memtest, TrafficGen or any Ruby tester are
affected and will be updated accordingly.

2 files changed, 14 insertions, 11 deletions

diff --git a/src/cpu/testers/rubytest/Check.cc b/src/cpu/testers/rubytest/Check.cc
index b2b679018..126deba6d 100644
--- a/src/cpu/testers/rubytest/Check.cc
+++ b/src/cpu/testers/rubytest/Check.cc
@@ -27,6 +27,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "base/random.hh"
 #include "cpu/testers/rubytest/Check.hh"
 #include "debug/RubyTest.hh"
 #include "mem/ruby/common/SubBlock.hh"
@@ -46,7 +47,8 @@ Check::Check(const Address& address, const Address& pc,
     pickInitiatingNode();
     changeAddress(address);
     m_pc = pc;
-    m_access_mode = RubyAccessMode(random() % RubyAccessMode_NUM);
+    m_access_mode = RubyAccessMode(random_mt.random(0,
+                                                    RubyAccessMode_NUM - 1));
     m_store_count = 0;
 }
 
@@ -57,11 +59,11 @@ Check::initiate()
     debugPrint();
 
     // currently no protocols support prefetches
-    if (false && (random() & 0xf) == 0) {
+    if (false && (random_mt.random(0, 0xf) == 0)) {
         initiatePrefetch(); // Prefetch from random processor
     }
 
-    if (m_tester_ptr->getCheckFlush() && (random() & 0xff) == 0) {
+        if (m_tester_ptr->getCheckFlush() && (random_mt.random(0, 0xff) == 0)) {
         initiateFlush(); // issue a Flush request from random processor
     }
 
@@ -81,7 +83,7 @@ Check::initiatePrefetch()
 {
     DPRINTF(RubyTest, "initiating prefetch\n");
 
-    int index = random() % m_num_readers;
+    int index = random_mt.random(0, m_num_readers - 1);
     MasterPort* port = m_tester_ptr->getReadableCpuPort(index);
 
     Request::Flags flags;
@@ -90,7 +92,7 @@ Check::initiatePrefetch()
     Packet::Command cmd;
 
     // 1 in 8 chance this will be an exclusive prefetch
-    if ((random() & 0x7) != 0) {
+    if (random_mt.random(0, 0x7) != 0) {
         cmd = MemCmd::ReadReq;
 
         // if necessary, make the request an instruction fetch
@@ -132,7 +134,7 @@ Check::initiateFlush()
 
     DPRINTF(RubyTest, "initiating Flush\n");
 
-    int index = random() % m_num_writers;
+    int index = random_mt.random(0, m_num_writers - 1);
     MasterPort* port = m_tester_ptr->getWritableCpuPort(index);
 
     Request::Flags flags;
@@ -161,7 +163,7 @@ Check::initiateAction()
     DPRINTF(RubyTest, "initiating Action\n");
     assert(m_status == TesterStatus_Idle);
 
-    int index = random() % m_num_writers;
+    int index = random_mt.random(0, m_num_writers - 1);
     MasterPort* port = m_tester_ptr->getWritableCpuPort(index);
 
     Request::Flags flags;
@@ -222,7 +224,7 @@ Check::initiateCheck()
     DPRINTF(RubyTest, "Initiating Check\n");
     assert(m_status == TesterStatus_Ready);
 
-    int index = random() % m_num_readers;
+    int index = random_mt.random(0, m_num_readers - 1);
     MasterPort* port = m_tester_ptr->getReadableCpuPort(index);
 
     Request::Flags flags;
@@ -339,7 +341,7 @@ Check::pickValue()
 {
     assert(m_status == TesterStatus_Idle);
     m_status = TesterStatus_Idle;
-    m_value = random() & 0xff; // One byte
+    m_value = random_mt.random(0, 0xff); // One byte
     m_store_count = 0;
 }
 
@@ -348,7 +350,7 @@ Check::pickInitiatingNode()
 {
     assert(m_status == TesterStatus_Idle || m_status == TesterStatus_Ready);
     m_status = TesterStatus_Idle;
-    m_initiatingNode = (random() % m_num_writers);
+    m_initiatingNode = (random_mt.random(0, m_num_writers - 1));
     DPRINTF(RubyTest, "picked initiating node %d\n", m_initiatingNode);
     m_store_count = 0;
 }
diff --git a/src/cpu/testers/rubytest/CheckTable.cc b/src/cpu/testers/rubytest/CheckTable.cc
index f10132c89..df2bf864d 100644
--- a/src/cpu/testers/rubytest/CheckTable.cc
+++ b/src/cpu/testers/rubytest/CheckTable.cc
@@ -28,6 +28,7 @@
  */
 
 #include "base/intmath.hh"
+#include "base/random.hh"
 #include "cpu/testers/rubytest/Check.hh"
 #include "cpu/testers/rubytest/CheckTable.hh"
 #include "debug/RubyTest.hh"
@@ -107,7 +108,7 @@ Check*
 CheckTable::getRandomCheck()
 {
     assert(m_check_vector.size() > 0);
-    return m_check_vector[random() % m_check_vector.size()];
+    return m_check_vector[random_mt.random<unsigned>(0, m_check_vector.size() - 1)];
 }
 
 Check*