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问题描述

_control87 注意:

SSE和SSE2 MXCSR控制寄存器相同,但是,文档中未提及SSE单元。 _control87 会影响SSE单元的MXCSR控制寄存器还是仅对SSE2有用?

It seems that the SSE and SSE2 MXCSR control registers are identical, however, there is no mention of the SSE unit in the documentation. Does _control87 affect an SSE unit's MXCSR control register or is this only true for SSE2?

推荐答案

我挖出一个旧的Pentium III,并用以下代码检查:

I dug out an old Pentium III and checked with the following code:

#include <Windows.h>
#include <float.h>
#include <xmmintrin.h>
#include <iostream>
#include <iomanip>

int _tmain( int argc, _TCHAR* argv[] ) {
    using namespace std;

    // Unmask all SSE/SSE2 exceptions
    _MM_SET_EXCEPTION_MASK( 0 );
    // Get SSE/SSE2 exception mask
    DWORD dwExceptionMask = _MM_GET_EXCEPTION_MASK();
    cout << "Exception Mask: 0x" << hex << setw( 8 )
         << setfill( '0' ) << dwExceptionMask << endl;

    // Mask all FPU exceptions
    _control87( 0xFFFF, _MCW_EM );

    // Get SSE/SSE2 exception mask
    dwExceptionMask = _MM_GET_EXCEPTION_MASK();
    cout << "Exception Mask: 0x" << hex << setw( 8 )
         << setfill( '0' ) << dwExceptionMask << endl;

    return 0;
}

奔腾III(SSE)的结果:

Result on Pentium III (SSE):

Exception Mask: 0x00000000
Exception Mask: 0x00000000

至强(SSE,SSE2,SSE3,SSSE3)的结果:

Result on Xeon (SSE, SSE2, SSE3, SSSE3):

Exception Mask: 0x00000000
Exception Mask: 0x00001e80

结果令人惊讶,但与文档一致。 _control87 仅在至少有一个SSE2单元可用时才对MXCSR控制寄存器产生影响。

The results are surprising, but in line with the documentation. _control87 only has an effect on the MXCSR control register if at least an SSE2 unit is available.

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07-10 03:54