call asm sqrtsd under a c++

问题

Under visual 2012 how can I call the sqrtsd asm function in a c++ project

I can't find it via google

something like :

double mySqrt(double val)
{
__asm
{
  ...
  sqrstd...
}
}

EDIT:

in 32bit mode

回答1:

I think doing this is a somewhat academic excercise, as it's unlikely to have any actual benefit, and quite likely a penalty. However:

double mySqrt(double val)
{
    double retu;

    __asm
    {
        sqrtsd xmm1, val
        movsd retu, xmm1
    }
    return retu;
}

回答2:

Why not using sqrt function http://www.cplusplus.com/reference/cmath/sqrt/ which will be portable ?

By default VS 2012 will replace sqrt() by __libm_sse2_sqrt_precise. But if you compile with /fp:fast it will replace by sqrtsd

回答3:

You may or may not be able to use inline assembler, as other answers have indicated.

There are, however so called intrinsics for SSE (and MMX and others):

intrinsic functons for MS VS

The one for sqrtsd is _mm_sqrt_sd

You'll obviously have to read a few of the other pages as well to be able to put together the whole thing. Intrinsics is the recommended way by Microsoft to solve this.

回答4:

what you want, the feature that you are looking for, it's called "inline assembly", meaning assembly inside a C/C++ program basically, Visual Studio doesn't offer a good support for this, for x64 bit platform it doesn't offer this feature at all.

http://www.viva64.com/en/k/0015/

You probably want to switch to a better compiler.

来源：https://stackoverflow.com/questions/14067236/call-asm-sqrtsd-under-a-c