微软.net精简框架常见问题及回答(中文版)(33)

王朝c#·作者佚名 2006-01-09

宽屏版字体: 小|中|大|超大

Me.bCancel = New Button()

Me.bCancel.Parent = Me

Me.bCancel.Bounds = New Rectangle(10, 50, 150, 30)

Me.bCancel.Text = "Cancel"

AddHandler Me.bCancel.Click, AddressOf Me._Click

End Sub 'New

Private Sub _Click(o As Object, e As EventArgs)

Me.Hide()

Me.myParent.DialogResultCallback(IIf(o Is Me.bOK, DialogResult.OK, DialogResult.Cancel))

End Sub '_Click

Protected Overrides Sub OnClosing(e As CancelEventArgs)

e.Cancel = True

Me.Hide()

Me.myParent.DialogResultCallback(DialogResult.Cancel)

End Sub 'OnClosing

End Class 'ModelessDialog

7.40. How do I round floating point numbers efficiently?

There are two primary methods for rounding numbers:

Convert.ToInt32

Cast or Fix (C# or VB) Convert.ToInt32 automatically handles rounding, where remainders of .5 and greater cause the number to be rounded up. Casting or using Fix requires adding .5 to the number to ensure that it will round properly, as these methods simply remove the remainder.

Profiling on the emulator and a Compaq iPAQ H3600 series device yielded the following results for 1 million operations of each method, where num is a float set to 3.6F:

Emulator

iPAQ

Operation

Debug (ms)

Release (ms)

Debug (ms)

Release (ms)

C#: Convert.ToInt32(num)

1321

1109

6264

6283

C#: (int)(num + .5F)

170

1479

VB: Convert.ToInt32(num)

1218

1232

6531

6517

VB: Fix(num + .5F)

3873

3677

18144

17955

Thus, by examining the release build results for the device, it can be concluded that on the current generation of devices it is most efficient to use casting in C# and Convert.ToInt32 in VB. In C#, casting proved to be over 106 times faster, whereas in VB, Convert.ToInt32 was nearly 3 times faster. //C#

float temp = 3.6f;

int rounded1 = (int)(temp + .5f);

int rounded2 = Convert.ToInt32(temp);