From: Dam Sunwoo <dam.sunwoo@arm.com>
Date: Tue, 10 Jan 2012 00:08:20 +0000 (-0600)
Subject: Base: Fixed shift amount in genrand() to work with large numbers
X-Git-Tag: stable_2012_06_28~275^2~39
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=3f9e352de4e1ac34e1f0b83c3f66af2175b524f4;p=gem5.git

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.
---

diff --git a/src/base/random.cc b/src/base/random.cc
index 457b0c98b..cffeddec9 100644
--- a/src/base/random.cc
+++ b/src/base/random.cc
@@ -29,6 +29,7 @@
  *          Ali Saidi
  */
 
+#include <limits>
 #include "base/fenv.hh"
 #include "base/intmath.hh"
 #include "base/misc.hh"
@@ -67,7 +68,10 @@ Random::genrand(uint32_t max)
 {
     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 @@ Random::genrand(uint64_t max)
 {
     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;