Floating Point arithmetic difference between VB and C#

Floating Point arithmetic difference between VB and C#

• dcritch

  Note: Moved it to DirectX General.
  
  
  

• Freek Bos

  OK, found what’s causing the problem: DirectX! After creating a device the error is present, see below. I will move this thread over to the directX forum.

  using System;

  using System.Windows.Forms;

  using Microsoft.DirectX;

  using Microsoft.DirectX.Direct3D;

  namespace WindowsApplication1

  {

  public partial class Form1 : Form

  {

  private Device m_device = null;

  public Form1()

  {

  InitializeComponent();

  }

  private void Form1_Load(object sender, EventArgs e)

  {

  PresentParameters presentParameters = new PresentParameters();

  presentParameters.Windowed = true;

  presentParameters.SwapEffect = SwapEffect.Discard;

  double a;

  double b;

  double c;

  a = 10002;

  b = 25;

  c = a * a + b * b;

  MessageBox.Show(String.Format("Result = {0}", c), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

  m_device = new Device(0, DeviceType.Hardware, this, CreateFlags.SoftwareVertexProcessing, presentParameters);

  a = 10002;

  b = 25;

  c = a * a + b * b;

  MessageBox.Show(String.Format("Result = {0}", c), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

  }

  }

  }

  
  

• Kiku

  This is a known “problem”. Direct3D works internally only with single precision and set the FPU flags during device creation. You can change this that it set and reset it anytime you call a Direct3D function and not global.

  Add CreateFlags.FpuPreserve to your create flags.

  
  
  

• carzyR

  Try to put a double value in your doubles and on an int value:
  
  

  double a,b,c; a = 10002d; b = 25d; c = a * a + b * b;

  
  
  
  

• joerage

  DirectX may change floating point precision when a device has been created with the default parameters (for more info, see this GameDev thead). You can tell MDX not to mess with this precision by including the CreateFlags.FpuPreserve flag when creating your D3D device, at the cost of a small performance penalty.
  
  

• RSatter

  Thanks for the reply, your comments prompted me to create a new test project and yes you are right it’s Ok in that one. Yes I’m just looking in the debugger as well.

  I have tried to see if there are any settings that are different, but to no avail. I had the test code in the event of a toolbar button, I have tried moving the code to different areas of my app and sometimes it works and sometimes not! I can’t find a pattern yet though.

  Not sure where to go from here!!

  
  

• AJ_101

  What can I say, thank you so much people!!

  Julian

  
  

• ocanon

  Hi, unfortunately that did not work, in my actual function that I found the problem in, the variables are actually arguments of type double. So I never assign any values as per the sample. The sample code is for simplicity to demonstrate the problem.

  Are there any advanced techniques for debugging at a lower level, I’m not sure how to proceed with the problem, I can’t thing of a way to provide an actual demo app without giving out my whole app.

  Thanks for you help in this matter

  Julian

  
  

• syouki

  It comes up with the right answer for me using VB with both VS2005 and VS2003.
  
  Something else must be going on... Did you try it in a completely-standard generated application How were you displaying the result I just looked at 'c' in the debugger.
  
  
  
• Floating Point arithmetic difference between VB and C#