Performance regression in VS2013 compared to earlier versions due to dtoui3 casting

Question

Copied from submitted bug report ID 1175765     
Description
Hello,
We have a performance bug with VS2013 that is not seen in earlier versions. The performance issue is due to casting problems similar
to reported problem, https://connect.microsoft.com/VisualStudio/feedback/details/808199. This problem was reported fix in
VS2013 SP2 but I can still reproduce problems with SP5 (12.0.40121). The difference is that I use IBM Rational Quantify to show the
performance callstack. You will see that the function, dtoui3, is calling dtol3_Nan for all 10 calls. This gives a significant slowdown in real
applications that cast millions of times. Please see below how to reproduce the problem.
Code example:
#include <limits>
#include <cstdio>
double foo() {
return 1.0;
int _tmain(int argc, _TCHAR* argv[])
for (int i = 0; i < 10; i++) {
unsigned d = static_cast<unsigned>(std::numeric_limits<double>::max() / 2.0);
printf("%f\n", foo());
return 0;
Build with VS2013 SP5. Test with IBM Rational Quantify. F_D time callstack shows dtoui3 calls dtol3_Nan 10 times.
Please note this problem is only 32bit. There is no problem for 64bit.
Please let me know if you need any more information.
Regards,
Dr. Ian Morgan.
Senior Support Engineer
MachineWorks

Answer 1

Hi MachineWorksUK,
>>VS2013 SP2 but I can still reproduce problems with SP5 (12.0.40121). The difference is that I use IBM Rational Quantify to show the
performance callstack.
Do you mean that you download the Update 5 CTP 3 here:
http://www.microsoft.com/en-us/download/details.aspx?id=45910
Since it worked well in update 2, but not work in update 5, I suggest you post a new feedback for this issue since this
feedback
shared by you has been closed, so submit a new one would be better:
http://connect.microsoft.com/VisualStudio/feedback/CreateFeedback.aspx
If you submit it, please share us the link here, so we could get the latest information from the connect members.
Best Regards,
Jack
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