[gem5-dev] changeset in gem5: Base: Fixed shift amount in genrand() to work...

[Dam Sunwoo]

changeset f1a69b7246f7 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=f1a69b7246f7
description:
        Base: Fixed shift amount in genrand() to work with large numbers

        The previous version didn't work correctly with max integer values 
(2^31-1 for
        32-bit, 2^63-1 for 64bit version), causing "shift" to become -1.  For 
smaller
        numbers, it wouldn't have caused functional errors, but would have 
resulted in
        more than necessary loops in the while loop.  Special-cased cases when 
(max + 1
        == 0) to prevent the ceilLog2 functions from failing.

diffstat:

 src/base/random.cc |  11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diffs (35 lines):

diff -r 776bc26ee1d4 -r f1a69b7246f7 src/base/random.cc
--- a/src/base/random.cc        Mon Jan 09 18:08:20 2012 -0600
+++ b/src/base/random.cc        Mon Jan 09 18:08:20 2012 -0600
@@ -29,6 +29,7 @@
  *          Ali Saidi
  */
 
+#include <limits>
 #include "base/fenv.hh"
 #include "base/intmath.hh"
 #include "base/misc.hh"
@@ -67,7 +68,10 @@
 {
     if (max == 0)
         return 0;
-    int log = ceilLog2(max) + 1;
+    if (max == std::numeric_limits<uint32_t>::max())
+        return genrand();
+
+    int log = ceilLog2(max + 1);
     int shift = (sizeof(uint32_t) * 8 - log);
     uint32_t random;
 
@@ -83,7 +87,10 @@
 {
     if (max == 0)
         return 0;
-    int log = ceilLog2(max) + 1;
+    if (max == std::numeric_limits<uint64_t>::max())
+        return genrand();
+
+    int log = ceilLog2(max + 1);
     int shift = (sizeof(uint64_t) * 8 - log);
     uint64_t random;
 
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