ShiftDate_Month

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zitz

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Joined: 05 October 2008
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Topic: ShiftDate_Month
Posted: 28 February 2009 at 2:30am

Hello. I use Xtreme ToolkitPro v13.0.0

AFX_INLINE BOOL CXTPCalendarUtils::ShiftDate_Month(COleDateTime &refDate, int nMonthCount)
{
    SYSTEMTIME sysDate;
    if (!GETASSYSTEMTIME_DT(refDate, sysDate))
        return FALSE;

    int nYearNew = sysDate.wYear + nMonthCount / 12;
    int nMonthNew = sysDate.wMonth + nMonthCount % 12;

    if (nMonthNew > 12)
    {
        nMonthNew -= 12 * (nMonthCount / abs(nMonthCount));
        nYearNew++;
    }
    else if (nMonthNew <= 0)
    {
        nYearNew--;
        nMonthNew += 12;

        ASSERT(nMonthNew >= 1 && nMonthNew <= 12);
    }

    return COleDateTime::valid == refDate.SetDate(nYearNew, nMonthNew, 1);
}

Function works wrong at release (Visual C++ 6.0) for nMonthCount = -1, I think because inline

For what?
nMonthNew -= 12 * (nMonthCount / abs(nMonthCount));
It is unnecessary here i think.
nMonthCount / abs(nMonthCount) == 1 always, or not?

mdoubson

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Posted: 28 February 2009 at 10:19am

I will check this - sorry - old strange class - i already fixed here serious bugs recently. But there was no complains on this function.

Btw - n / abs(n) can also be -1 and compiler shoud understand it.

zitz

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Posted: 28 February 2009 at 1:14pm

mdoubson wrote:

Btw - n / abs(n) can also be -1 and compiler shoud understand it.

No, it can't. If nMountCount < 0 then

if (nMonthNew > 12) <---- FALSE

I think it was without "if" in former times, for example

 int nYearNew = sysDate.wYear + nMonthCount / 12;
 int nMonthNew = sysDate.wMonth + nMonthCount % 12;
 nMonthNew -= 12 * (nMonthCount / abs(nMonthCount));
 nYearNew += nMonthCount / abs(nMonthCount);
 ASSERT(nMonthNew >= 1 && nMonthNew <= 12);

and if nMountCount == 0 --> crash

mdoubson

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Posted: 28 February 2009 at 2:18pm

No - I checked SVN - this version identical to Nov 2008 version (Rev 12.1)

I can cofirm the bug you found.

this is old code:

AFX_INLINE BOOL CXTPCalendarUtils::ShiftDate_Month(COleDateTime &refDate, int nMonthCount)
{
SYSTEMTIME sysDate;
if (!GETASSYSTEMTIME_DT(refDate, sysDate))
return FALSE;

int nYearNew = sysDate.wYear + nMonthCount / 12;
int nMonthNew = sysDate.wMonth + nMonthCount % 12;

if (nMonthNew > 12)
{
     nMonthNew -= 12 * (nMonthCount / abs(nMonthCount));
     nYearNew++;
}
else if (nMonthNew <= 0)
{
     nYearNew--;
     nMonthNew += 12;

ASSERT(nMonthNew >= 1 && nMonthNew <= 12);
}

return COleDateTime::valid == refDate.SetDate(nYearNew, nMonthNew, 1);

}

Unfortunately % operator in MS doing not proper modulo arithm - in math it suppose to give you positive result or nul - in MS - NOT:

COleDateTime refDate(2000,1,1,0,0,0);

SYSTEMTIME sysDate;

if (GETASSYSTEMTIME_DT(refDate, sysDate))

{

int nYearNew, nMonthNew, nMonthCount;

for (nMonthCount = -20; nMonthCount < 20; nMonthCount++)

{

//modulo operation debug:

nYearNew = sysDate.wYear + (sysDate.wMonth + nMonthCount) / 12;

nMonthNew = 1 + ((int) (sysDate.wMonth) + nMonthCount - 1) % 12;

===> it give nMonthNew = -7 in first loop step!

//this is old code debug:

nYearNew = sysDate.wYear + nMonthCount / 12;

nMonthNew = sysDate.wMonth + nMonthCount % 12;

nMonthNew -= 12 * (nMonthCount / abs(nMonthCount));

nYearNew += nMonthCount / abs(nMonthCount);

ASSERT(nMonthNew >= 1 && nMonthNew <= 12);

this code give ASSERTION with nMonthNew = 13

}

mdoubson

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Posted: 28 February 2009 at 5:42pm

The formula is very simple:

AFX_INLINE BOOL CXTPCalendarUtils::ShiftDate_Month(COleDateTime &refDate, int nMonthCount)

{

int nYearOld = refDate.GetYear();

int nMonthOld = refDate.GetMonth();

int nYearNew = nYearOld + (-12 + nMonthOld + nMonthCount) / 12;

int nMonthCalc = nMonthOld + nMonthCount - 1;

if (nMonthCalc < 0)

nMonthCalc = 12 * (-nMonthCalc) + nMonthCalc;

int nMonthNew = 1 + nMonthCalc % 12;

return COleDateTime::valid == refDate.SetDate(nYearNew, nMonthNew, 1);

}

I already update SVN. Thank you!