战俘实施双 [英] Pow implementation for double

问题描述

我开发一个code将被用于运动控制和我有战俘功能的问题。
我使用VS2010为IDE。

下面是我的问题：
我有：

 双P = 100.0000;
    双D = 1000.0000;
    T1 = POW（（P /（8.0000 * D）1.00 / 4.000）;
 

在评价这最后的功能，我没有得到更好的近似作为结果。我得到一个7位十进制数字正确，以及随之而来的数字都是垃圾。
我猜测战俘功能只投下任何输入变量为float和计算proceds。

1. 我说得对不对？


2. 如果是这样，没有任何code，我可以得到启发与重新实现战俘美好precision？

编辑：解决

毕竟，我是有其正在使用OGRE 3D框架FPU配置位，造成Direct3D的问题。

如果使用OGRE，在配置界面，只需设置浮点模式=一致。

如果使用原始的Direct3D，调用CreateDevice的时候，一定要通过D3DCREATE_FPU_ preSERVE标志吧。

原帖：

  

您可能正在使用正在改变默认的precision一个libray
  FPU的单幅precision。然后，所有的浮点运算，甚至
  在双打中，实际上将作为单precision操作执行。

  
  

作为一个测试，你可以尝试调用_controlfp（_CW_DEFAULT，0xfffff）;
  执行计算之前（您需要包括）
  看看你是否得到正确的结果。这将重置浮点
  控制字为默认值。请注意，它会重置其他设置
  同时，这可能会导致问题。

  
  

这改变了浮点precision一个常见的​​库
  9的Direct3D（也许其他版本太）：默认情况下，它改变了
  FPU创建一个设备时，单幅precision。如果你使用它，指定
  创建设备到prevent当标志D3DCREATE_FPU_ preSERVE它
  从改变FPU precision。

解决方案

您可以使用正在改变FPU的默认precision单幅precision一个libray。然后，所有的浮点运算，甚至在双击 S，实际上将作为单precision操作执行。

作为一个测试，你可以尝试调用 _controlfp（_CW_DEFAULT，0xfffff）; （您需要包括＆LT; FLOAT.H＆GT; ）。这将重置浮点控制字为默认值。请注意，它会重置其他设置为好，这可能会导致问题。

这改变了浮点precision一个共同库的Direct3D 9（也许其他版本太）：默认情况下，它改变了FPU创建一个设备时，单幅precision。如果你使用它，请指定标志创建设备prevent当 D3DCREATE_FPU_ preSERVE 从改变FPU precision。

I am developing a code that will be used for motion control and I am having a issue with the pow function. I am using VS2010 as IDE.

Here is my issue: I have:

    double p = 100.0000;
    double d = 1000.0000;
    t1 = pow((p/(8.0000*d),1.00/4.000);

When evaluating this last function, I don't get the better approximation as result. I am getting a 7 decimal digits correct, and the consequent digits are all trash. I am guessing that pow function only casts any input variable as float and proceds with calculation.

1. Am I right?
2. If so, is there any code I can get "inspired" with to reimplement pow for a better precision?

Edit: Solved.

After all, I was having problems with FPU config bits, caused by Direct3D which was being used by OGRE 3D framework.

If using OGRE, on the config GUI, just set "Floating-point mode=Consistent".

If using raw Direct3D, when calling CreateDevice, make sure to pass "D3DCREATE_FPU_PRESERVE" flag to it.

Original post:

You may be using a libray that is changing the default precision of the FPU to single-precision. Then all floating-point operations, even on doubles, will actually be performed as single-precision operations.

As a test, you can try calling _controlfp( _CW_DEFAULT, 0xfffff ); (you need to include ) before performing the calculation to see if you get the correct result. This will reset the floating-point control word to default values. Note that it will reset other settings as well, which may cause issues.

One common library that changes the floating-point precision is Direct3D 9 (and maybe other versions too): By default, it changes the FPU to single-precision when creating a device. If you use it, specify the flag D3DCREATE_FPU_PRESERVE when creating the device to prevent it from changing the FPU precision.

解决方案

You may be using a libray that is changing the default precision of the FPU to single-precision. Then all floating-point operations, even on doubles, will actually be performed as single-precision operations.

As a test, you can try calling _controlfp( _CW_DEFAULT, 0xfffff ); (you need to include <float.h>) before performing the calculation to see if you get the correct result. This will reset the floating-point control word to default values. Note that it will reset other settings as well, which may cause issues.

One common library that changes the floating-point precision is Direct3D 9 (and maybe other versions too): By default, it changes the FPU to single-precision when creating a device. If you use it, specify the flag D3DCREATE_FPU_PRESERVE when creating the device to prevent it from changing the FPU precision.

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