FIX: Bitwise shift operators return incorrect results when you run an application that is compiled by the Visual C++ 2010 x86 compiler

Consider the following scenario:
  • You use Microsoft Visual Studio 2010 Service Pack 1 (SP1) to develop a Visual C++ application.
  • The source code of the application uses bitwise shift operators (<< or >>).
  • You configure the application to target the x86 platform.
  • You compile the application by using the /O2 (Maximize Speed) or /Ox (Full Optimization) optimization option.
  • You run the application.
In this scenario, the bitwise shift operators may return incorrect results.

Note This issue does not occur in Microsoft Visual Studio 2012.

Hotfix information

A supported hotfix is now available from Microsoft. However, it is intended to correct only the problem that this article describes. Apply it only to systems that are experiencing this specific problem.

To resolve this problem, contact Microsoft Customer Support Services to obtain the hotfix. For a complete list of Microsoft Customer Support Services telephone numbers and information about support costs, visit the following Microsoft website:Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.


To apply this hotfix, you must have Visual Studio 2010 Service Pack 1 (SP1) installed.

Restart requirement

You do not have to restart the computer after you apply this hotfix if the affected files are not being used. We recommend that you close Visual Studio 2010-related components before you apply this hotfix.

File information

The global version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
File nameFile versionFile sizeDateTimePlatform

More information
To reproduce this issue, create a Visual C++ 2010 application that contains the following code:
#include <stdio.h>#include <memory.h>int main(int argc, char ** argv){	short lActualOutput;	const char * mBytes;	char x[5];	char lBuffer[2];		for (int i = 0; i < 5; i++)			{				x[i] = 97+i;			}		mBytes=&x[3];		size_t aSize = sizeof(lBuffer);		memcpy(lBuffer, mBytes, aSize);		mBytes += aSize;		lActualOutput = (lBuffer[0] << 8) + lBuffer[1];		fprintf(stdout, "lActualOutput= 0x%04X \n", lActualOutput);}

Then, configure the application to target the x86 platform, and compile the application by using the /O2 or /Ox optimization option. You will receive the following incorrect result:
lActualOutput= 0x6464
The expected result is as follows: 
lActualOutput= 0x6465
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
To work around this issue, use the optimize pragma to turn off the optimization for the problematic function(s).

For more information about the optimize pragma, go to the following MSDN website:
For more information about /O optimization options, go to the following MSDN website: For more information about bitwise shift operators, go to the following MSDN website:

Article ID: 2820057 - Last Review: 03/28/2013 05:46:00 - Revision: 3.0

Microsoft Visual Studio 2010 Service Pack 1, Microsoft Visual Studio 2010 Ultimate, Microsoft Visual Studio 2010 Professional, Microsoft Visual Studio 2010 Premium

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