call asm sqrtsd under a c++

Question

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

Something like `push argument \r\n call sqrt`, however you'll need 1. the mangled name of `std::sqrt()`, 2. a good assembly tutorial. — , Dec 28 '12 at 09:21
A related question [Is it possible to roll a significantly faster version of sqrt?](http://stackoverflow.com/questions/2637700/is-it-possible-to-roll-a-significantly-faster-version-of-sqrt) — Bo Persson, Dec 28 '12 at 09:43

benjarobin · Answer 1 · 2012-12-28T09:53:47.937

3

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

edited Dec 28 '12 at 09:53

answered Dec 28 '12 at 09:31

benjarobin

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I would like to be sure of the asm code, cause I can have a call to __libm_sse2_sqrt_precise – Guillaume Paris Dec 28 '12 at 09:44
2

Compile with /fp:fast to get the compiler to directly emit sqrtpd without using a library function. – Hans Passant Dec 28 '12 at 09:48

score 2 · Answer 2 · answered Dec 28 '12 at 09:46

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.

score 2 · Accepted Answer · edited Jan 02 '13 at 22:11

2

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;
}

edited Jan 02 '13 at 22:11

Guillaume Paris

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answered Dec 28 '12 at 09:54

JasonD

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score 0 · Answer 4 · answered Dec 28 '12 at 09:25

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.

call asm sqrtsd under a c++

4 Answers4

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