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

["Gao, Liming" <liming.gao@intel.com>]

Hao:
  I sent another patch to introduce CacluateCrc32() API in BaseLib. It will update MdeModulePkg Crc32 to depend on BaseLib. And, BaseLib CacluateCrc32() has no such logic. So, I think this patch is not necessary. 

Thanks
Liming
>-----Original Message-----
>From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Hao
>Wu
>Sent: Thursday, September 21, 2017 2:46 PM
>To: edk2-devel@lists.01.org
>Cc: Wu, Hao A <hao.a.wu@intel.com>; Paolo Bonzini <pbonzini@redhat.com>;
>Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
>Subject: [edk2] [PATCH v2 5/6] MdeModulePkg/Crc32: Fix possible out of
>range left shift
>
>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
>
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