Q248137: BUG: COleCurrency::operator/() Not Backward Compatible
Article: Q248137
Product(s): Microsoft C Compiler
Version(s): winnt:6.0
Operating System(s):
Keyword(s): kbAutomation kbMFC kbVC420 kbVC500 kbVC600bug kbGrpDSMFCATL
Last Modified: 07-MAY-2001
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The information in this article applies to:
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
- The Microsoft Foundation Classes (MFC)
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SYMPTOMS
========
When an application developed with Visual C++ 6.0 using MFC dynamically is
installed on a computer, it may cause existing applications built with Visual
C++ 4.2 or 5.0 that use MFC dynamically to stop working as expected.
Specifically, calculations that are done using the COleCurrency::operator/()
function may give incorrect results. It does not cause existing applications
built with Visual C++ 4.2 or 5.0 that use the COleCurrency::operator/() function
and MFC statically to behave differently.
CAUSE
=====
This is a bug in the Visual C++ 6.0 MFC COleCurrency class. The Visual C++ 6.0
MFC code for the COleCurrency::operator/() function does an incorrect
calculation. This results in incorrect results after this function is called.
RESOLUTION
==========
For any existing applications relying on the functionality of the
COleCurrency::operator/() function that shipped in MFC42.DLL with Visual C++ 4.2
or 5.0, you can copy the older Mfc42.dll into the application's directory. By
doing so, the older Mfc42.dll is not used nor the newer one located in the
windows system directory. If you are using Visual C++ 4.2 or 5.0 currently, you
could link to MFC statically to prevent using any version of Mfc42.dll that may
be on the target machines.
For newer applications being developed with Visual C++ 6.0, the best solution is
to not call COleCurrency::operator/(). You can work around the bug in Visual C++
6.0 by writing a new class that subclasses COleCurrency. To do so, add a new
header file to your project called MyOleCurrency.h and insert the following code
into it:
#ifndef MYOLECURRENCY_H
#define MYOLECURRENCY_H
// Return the highest order bit composing dwTarget in wBit.
#define HI_BIT(dwTarget, wBit) do \
{ \
if (dwTarget != 0) \
for (wBit = 32; (dwTarget & (0x00000001 << (wBit-1))) == 0; wBit--) \
; \
else \
wBit = 0; \
} while (0)
// Left shift an (assumed unsigned) currency by wBits.
#define LSHIFT_UCUR(cur, wBits) do \
{ \
for (WORD wTempBits = wBits; wTempBits > 0; wTempBits--) \
{ \
cur.m_cur.Hi = ((DWORD)cur.m_cur.Hi << 1); \
cur.m_cur.Hi |= (cur.m_cur.Lo & 0x80000000) >> 31; \
cur.m_cur.Lo = cur.m_cur.Lo << 1; \
} \
} while (0)
// Right shift an (assumed unsigned) currency by wBits.
#define RSHIFT_UCUR(cur, wBits) do \
{ \
for (WORD wTempBits = wBits; wTempBits> 0; wTempBits--) \
{ \
cur.m_cur.Lo = cur.m_cur.Lo >> 1; \
cur.m_cur.Lo |= (cur.m_cur.Hi & 0x00000001) << 31; \
cur.m_cur.Hi = ((DWORD)cur.m_cur.Hi >> 1); \
} \
} while (0)
#define DELETE_EXCEPTION(e) do { e->Delete(); } while (0)
class CMyOleCurrency : public COleCurrency
{
public:
const COleCurrency& operator=(CURRENCY cySrc)
{
m_cur = cySrc;
SetStatus(valid);
return *this;
}
const COleCurrency& operator=(const COleCurrency& curSrc)
{
m_cur = curSrc.m_cur;
m_status = curSrc.m_status;
return *this;
}
const COleCurrency& operator=(const VARIANT& varSrc)
{
if (varSrc.vt != VT_CY)
{
TRY
{
COleVariant varTemp(varSrc);
varTemp.ChangeType(VT_CY);
m_cur = varTemp.cyVal;
SetStatus(valid);
}
// Catch COleException from ChangeType, but not CMemoryException
CATCH(COleException, e)
{
// Not able to convert VARIANT to CURRENCY
m_cur.Hi = 0;
m_cur.Lo = 0;
SetStatus(invalid);
DELETE_EXCEPTION(e);
}
END_CATCH
}
else
{
m_cur = varSrc.cyVal;
SetStatus(valid);
}
return *this;
}
COleCurrency CMyOleCurrency::operator/(long nOperand) const
{
// If operand not Valid, just return
if (!GetStatus() == valid)
return *this;
COleCurrency curTemp(m_cur);
DWORD nTempOp;
// Check for divide by 0b
if (nOperand == 0)
{
curTemp.SetStatus(invalid);
// Set to maximum negative value
curTemp.m_cur.Hi = 0x80000000;
curTemp.m_cur.Lo = 0x00000000;
return curTemp;
}
// Compute absolute values
if (curTemp.m_cur.Hi < 0)
curTemp = -curTemp;
nTempOp = labs(nOperand);
// Optimization - division is simple if Hi == 0
if (curTemp.m_cur.Hi == 0x0000)
{
//vc5 SP3 done this..., changed back to VC++ 5.0 SP3 behavior
curTemp.m_cur.Lo /= nTempOp;
//vc6 did this...
//curTemp.m_cur.Lo = m_cur.Lo / nTempOp;
// Compute result sign
if ((m_cur.Hi ^ nOperand) & 0x80000000)
curTemp = -curTemp;
return curTemp;
}
// Now curTemp represents remainder
COleCurrency curResult; // Initializes to zero
COleCurrency curTempResult;
COleCurrency curOperand;
curOperand.m_cur.Lo = nTempOp;
WORD wHiBitRem;
WORD wScaleOp;
// Quit if remainder can be truncated
while (curTemp >= curOperand)
{
// Scale up and divide Hi portion
HI_BIT(curTemp.m_cur.Hi, wHiBitRem);
if (wHiBitRem != 0)
wHiBitRem += 32;
else
HI_BIT(curTemp.m_cur.Lo, wHiBitRem);
WORD wShift = (WORD)(64 - wHiBitRem);
LSHIFT_UCUR(curTemp, wShift);
// If Operand bigger than Hi it must be scaled
wScaleOp = (WORD)((nTempOp > (DWORD)curTemp.m_cur.Hi) ? 1 : 0);
// Perform synthetic division
curTempResult.m_cur.Hi = (DWORD)curTemp.m_cur.Hi / (nTempOp >> wScaleOp);
// Scale back to get correct result and remainder
RSHIFT_UCUR(curTemp, wShift);
wShift = (WORD)(wShift - wScaleOp);
RSHIFT_UCUR(curTempResult, wShift);
// Now calculate result and remainder
curResult += curTempResult;
curTemp -= curTempResult * nTempOp;
}
// Compute result sign
if ((m_cur.Hi ^ nOperand) & 0x80000000)
curResult = -curResult;
return curResult;
}
};
#endif MYOLECURRENCY_H
Instead of using COleCurrency in your code, use CMyOleCurrency instead. Also, be
sure to use #include "MyOleCurrency.h" after #include "stdafx.h" before using
the CMyOleCurrency class in any source files.
STATUS
======
Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.
MORE INFORMATION
================
Steps to Reproduce Behavior
---------------------------
1. Using Visual C++ 6.0, create a new Win32 Console Application with AppWizard.
Type TestCurr in the Project name edit box. Click the OK button.
2. In the next dialog box, click the radio button An application that supports
MFC. Click Finish. Click OK in the New Project Information dialog box.
3. Open the TestCurr.cpp file and add the following code below before the return
statement in _tmain:
COleCurrency a;
a.SetCurrency (4,500);
a *= -100;
a=a/100;
cout << "Hi = " << a.m_cur.Hi << endl;
cout << "Lo = " << a.m_cur.Lo << endl;
cout << "int64 = " << (INT)a.m_cur.int64 << endl;
4. The code for _tmain() should look something like the following after doing
the last step:
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
int nRetCode = 0;
// initialize MFC and print and error on failure
if (!AfxWinInit(::GetModuleHandle(NULL), NULL, ::GetCommandLine(), 0))
{
// TODO: change error code to suit your needs
cerr << _T("Fatal Error: MFC initialization failed") << endl;
nRetCode = 1;
}
else
{
// TODO: code your application's behavior here.
CString strHello;
strHello.LoadString(IDS_HELLO);
cout << (LPCTSTR)strHello << endl;
}
COleCurrency curr;
curr.SetCurrency (4,500);
curr *= -100;
curr = curr/100;
cout << "Hi = " << curr.m_cur.Hi << endl;
cout << "Lo = " << curr.m_cur.Lo << endl;
cout << "int64 = " << (INT)curr.m_cur.int64 << endl;
return nRetCode;
}
5. Build the project and execute it.
You should see the following in the output window for the results of the
calculations:
Hi = -1
Lo = 4252058124
Int64 = -42909172
If the same code was compiled using Visual C++ 4.2 or 5.0, you get the following
results instead:
Hi = -1
Lo = 4294926796
int64 = -40500
Additional query words: backward compatible port incompatible wrong results answer MFC42.DLL
======================================================================
Keywords : kbAutomation kbMFC kbVC420 kbVC500 kbVC600bug kbGrpDSMFCATL
Technology : kbVCsearch kbAudDeveloper kbMFC kbVC600 kbVC32bitSearch
Version : winnt:6.0
Issue type : kbbug
Solution Type : kbpending
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