使用SEH时如何使用_controlfp_s？

Question

我一直在尝试编写一些错误保护条款来识别第三方提供给我们的dll 中的问题。这个dll可能存在问题（内存异常，浮点数错误等），最好能在不访问源代码的情况下识别这些错误。

我从各种 SEH 错误处理例程中收集了一些东西，但尽管它有效，但有几个...与它不一致。我试图将每一个都隔离开来，我将针对每一个单独问一个问题。

这与使用 _controlfp_s 设置和重置浮点错误行为有关。

// For floating point protection ---------
#include <float.h>      // defines of _EM_OVERFLOW, etc.
#include <string.h>     // strncpy_s & strncat_s
#include <stdlib.h>     // malloc
#include <excpt.h>      // EXCEPTION_EXECUTE_HANDLER
#include <iostream>     // cout
#include <bitset>       // bitset
#include <conio.h>      // _kbhit
#pragma fenv_access (on)
// ---------------------------------------


const unsigned int SERIOUS_FP_EXCEPTIONS = _EM_DENORMAL | _EM_ZERODIVIDE | _EM_INVALID;
const unsigned int MINOR_FP_EXCEPTIONS = _EM_OVERFLOW | _EM_UNDERFLOW | _EM_INEXACT;

int main(int argc, char[])
{
    double numerator = 1.0;
    double denominator = 0.0;
    double result = 0.0;


    unsigned int _previous_floating_point_control;
    unsigned int _current_floating_point_control;

    _controlfp_s(&_current_floating_point_control, 0, 0);
    std::cout << "Floating point word originally:       " << std::bitset<32>(_current_floating_point_control) << std::endl;
    std::cout << "New settings to add:                  " << std::bitset<32>(MINOR_FP_EXCEPTIONS) << std::endl;
    std::cout << "With the mask:                        " << std::bitset<32>(_MCW_EM) << std::endl;

    _controlfp_s(&_previous_floating_point_control, MINOR_FP_EXCEPTIONS, _MCW_EM);      // This should appear to work, according to the documentation.
    std::cout << "Floating point word cached:           " << std::bitset<32>(_previous_floating_point_control) << std::endl;

    /* This works:
    _controlfp_s(&_previous_floating_point_control, 0, 0);      // This should appear to work, according to the documentation.
    _controlfp_s(nullptr, MINOR_FP_EXCEPTIONS, _MCW_EM);      // This should appear to work, according to the documentation.
    std::cout << "Floating point word cached:           " << std::bitset<32>(_previous_floating_point_control) << std::endl;
    */

    _controlfp_s(&_current_floating_point_control, 0, 0);
    std::cout << "Floating point word used:             " << std::bitset<32>(_current_floating_point_control) << std::endl;

    __try {
        result = numerator / denominator;
        _controlfp_s(NULL, _previous_floating_point_control, _MCW_EM);
        std::cout << "No error detected." << std::endl;
    }
    __except (EXCEPTION_EXECUTE_HANDLER)
    {
        std::cout << "Error code is:                        " << std::bitset<32>(GetExceptionCode()) << std::endl;
        if ((GetExceptionCode() & _EM_INVALID) || (GetExceptionCode() & _EM_ZERODIVIDE) || (GetExceptionCode() & _EM_DENORMAL))
            std::cout << "ERROR! Serious floating point error!" << std::endl;
        else
            std::cout << "Something else..." << std::endl;

        _controlfp_s(NULL, _previous_floating_point_control, _MCW_EM);

        _controlfp_s(&_current_floating_point_control, 0, 0);
        std::cout << "Floating point word reset to:         " << std::bitset<32>(_current_floating_point_control) << std::endl;

    }

    std::cout << "result = " << result << std::endl;

    while (!_kbhit())   // Wait until a key is pressed to close console.
    { }
}

这会产生：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000000000000000000000111
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000000111
Floating point word used:             00000000000010010000000000000111
ERROR! Serious floating point error!
Floating point word reset to:         00000000000010010000000000000111
result = 0

请注意 _previous_floating_point_control 实际上设置为 new 值，因此最后重置它的努力没有任何作用。

这是正确的行为（分两步使用 _controlfp_s）：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000000000000000000000111
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000000111
ERROR! Serious floating point error!
Floating point word reset to:         00000000000010010000000000011111
result = 0

我认为这是一个错误，既然我有办法解决它，我很乐意忽略它。

但情况变得更糟：如果您注意到，上面的示例（有效）将浮点字设置为 MINOR_FP_EXCEPTIONS，并且成功地获取了 SERIOUS_FP_EXCEPTIONS。如果我尝试替换它：

_controlfp_s(&_previous_floating_point_control, SERIOUS_FP_EXCEPTIONS, _MCW_EM);

产量：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000010000000000000011000
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000011000
No error detected.
result = 1.#INF


_controlfp_s(&_previous_floating_point_control, 0, _MCW_EM);

产量：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000000000000000000000000
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000000000
Error code is:                        11000000000000000000001010110101
ERROR! Serious floating point error!
Floating point word reset to:         00000000000010010000000000011111
result = 0

并且： _controlfp_s(nullptr, _MCW_EM, _MCW_EM); 产量：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000010000000000000011111
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000011111
No error detected.
result = 1.#INF

总结一下：

_controlfp_s 不会 "get" 旧的浮点字作为 "set" 的副产品，但如果您在单独的操作中执行它。
要捕获严重的浮点错误，您需要设置 _controlfp_s 以查找次要 f.p.e.s 而不是主要错误。
[无法识别被零除的问题在其他问题之一]

我是不是误解了整个领域？

Answer 1

我想我会冒险回答这个问题，因为我对我的相关问题有一个非常有用的回答：。

通过实验，_controlfp_s 的新设置似乎是要忽略的异常，而不是要应对的异常。我找到了关于这个的官方文档...不清楚。

关于f.p返回旧值的问题。设置新的时说：我相信这是一个错误 - 或者至少是不受欢迎的行为。文档明确指出 _controlfp_s 将在掩码为 0 时填充旧值，但没有提及其他情况。在几乎所有类似的功能中，我希望您能够在一个操作中完成获取和设置 - 而不是一个作为获取或集合操作的函数。

使用SEH时如何使用_controlfp_s？

How do I use _controlfp_s when using SEH?

c++

floating-point

seh