为什么浮点数和整数之间的乘法在C＃中与C ++和FORTRAN 77不同 [英] Why is Multiplication Between a Float and a Integer Different in C# Than C++ and FORTRAN 77

问题描述

我正在努力将FORTRAN 77中的一些代码转换为C＃。我遇到了一个问题，即相同的外观表达式返回的结果与其他语言不同。例如：

下面的C＃代码显示整数640437496

 float f = .29822734f; 
 int i =（int）（f * 2147480832）; 
 Console.WriteLine（i）; 

下面的C ++代码显示整数640437504

< pre class ="prettyprint"style =""> float f = .29822734;
int i =（int）（f * 2147480832）;
std :: cout<< "i =" << i;

最后，这个FORTRAN 77代码与C ++共享结果：  640437504

整数i 
实数f 
f = .29822734 
i = int（f * 2147480832）
写（*，*）i 

<我找不到其他人在为此苦苦挣扎？我是否错过了与C＃中的C ++和FORTRAN不同的标准？我做错了什么？

感谢您的帮助。

解决方案

尝试调查：在C＃中，转到Build菜单，Configuration Manager，然后添加新的"x86"和"x64"平台。检查每种情况下的结果。

似乎在"x86"平台中你可以使用
设置精度 _ controlfp_s 功能。它在C ++中可用，但您可以尝试在C＃中调用它：

[DllImport（
" msvcrt" ，CallingConvention = CallingConvention.Cdecl）]

static
extern
int _controlfp_s（
out
uint currentControl，
uint newControl，
uint mask）;

 

const
uint _MCW_PC = 0x00030000;

const
uint _PC_24 = 0x00020000;

const
uint _PC_53 = 0x00010000;

const
uint _PC_64 = 0x00000000;

 

..

uint cc;

 

_ controlfp_s（
out cc，_PC_24，_MCW_PC）;

{

   
浮动 f = .29822734f;

   
int i =（ int ）（
f * 2147480832）;

   
Console.WriteLine（i）;

}

 

_ controlfp_s（
out cc，_PC_64，_MCW_PC）;

{

   
浮动 f = .29822734f;

   
int i =（ int ）（
f * 2147480832）;

   
Console.WriteLine（i）;

}

 

在"x86"平台的情况下检查这些结果。

I am working on translating a bit of code from FORTRAN 77 to C#. I ran into the problem that an identical looking expression is returning different results than in other languages. For Example:

The C# code below displays the integer 640437496

float f = .29822734f;
int i = (int)(f * 2147480832);
Console.WriteLine(i);

The C++ code below displays the integer 640437504

float f = .29822734;
int i = (int)(f * 2147480832);
std::cout << "i = " << i;

Finally, this FORTRAN 77 code shares the result with C++: 640437504

integer i
real f
f = .29822734
i = int(f * 2147480832)
write ( *, * ) i

I can't find any other people struggling with this? Did I miss a standard that is different from C++ and FORTRAN in C#? Did I do something wrong?

Thanks for the help.

解决方案

Try an investigation: in C#, go to Build menu, Configuration Manager, and add new "x86" and "x64" platforms. Check the results in each case.

Seems that in "x86" platform you can set the precision using the _controlfp_s function. It is available in C++, but you can try calling it in C# to:

[DllImport( "msvcrt", CallingConvention = CallingConvention.Cdecl )]

static extern int _controlfp_s( out uint currentControl, uint newControl, uint mask );

 

const uint _MCW_PC = 0x00030000;

const uint _PC_24 = 0x00020000;

const uint _PC_53 = 0x00010000;

const uint _PC_64 = 0x00000000;

 

. . .

uint cc;

 

_controlfp_s( out cc, _PC_24, _MCW_PC );

{

    float f = .29822734f;

    int i = (int)( f * 2147480832 );

    Console.WriteLine( i );

}

 

_controlfp_s( out cc, _PC_64, _MCW_PC );

{

    float f = .29822734f;

    int i = (int)( f * 2147480832 );

    Console.WriteLine( i );

}

 

Check these results in case of "x86" platform.

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