[PATCH v2 5/6] MdeModulePkg/Crc32: Fix possible out of range left shift

[Hao Wu <hao.a.wu@intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=697

Within function ReverseBits(), left shift operations of 1 in the
following statements:
"(1 << Index)" and "(1 << (31 - Index))"

will incur possible out of range left shift when Index is either 0 or
31, since "1 << 31" is possible to exceed the range of type 'int'
(signed).

According to the C11 spec, Section 6.5.7:
> 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated
>   bits are filled with zeros. If E1 has an unsigned type, the value
>   of the result is E1 * 2^E2 , reduced modulo one more than the
>   maximum value representable in the result type. If E1 has a signed
>   type and nonnegative value, and E1 * 2^E2 is representable in the
>   result type, then that is the resulting value; otherwise, the
>   behavior is undefined.

This commit uses '1U' instead of '1' to resolve this issue.

Cc: Steven Shi <steven.shi@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
---
 MdeModulePkg/Core/RuntimeDxe/Crc32.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Core/RuntimeDxe/Crc32.c b/MdeModulePkg/Core/RuntimeDxe/Crc32.c
index a6fe77fa34..2cd234b562 100644
--- a/MdeModulePkg/Core/RuntimeDxe/Crc32.c
+++ b/MdeModulePkg/Core/RuntimeDxe/Crc32.c
@@ -7,7 +7,7 @@
   EFI Runtime Services Table are converted from physical address to
   virtual addresses.  This requires that the 32-bit CRC be recomputed.
 
-Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
 This program and the accompanying materials
 are licensed and made available under the terms and conditions of the BSD License
 which accompanies this distribution.  The full text of the license may be found at
@@ -79,8 +79,8 @@ ReverseBits (
 
   NewValue = 0;
   for (Index = 0; Index < 32; Index++) {
-    if ((Value & (1 << Index)) != 0) {
-      NewValue = NewValue | (1 << (31 - Index));
+    if ((Value & (1U << Index)) != 0) {
+      NewValue = NewValue | (1U << (31 - Index));
     }
   }
 
-- 
2.12.0.windows.1