Right shift operation not working

[NK-Nikunj]

Issue type: Error

While utilizing the Right shift and Left shift bitwise operators, I'm getting an error:

/home/nk/opt/nsimd/include/nsimd/cxx_adv_api_functions.hpp:998:16: error: no matching function for call to ‘shr(const simd_vector&, int&, float, nsimd::cpu)’
  998 |   ret.car = shr(a0.car, a1, T(), SimdExt());

Reproducing the error

Here is the minimal program to reproduce the issue:

#include <iostream>
#include <nsimd/nsimd-all.hpp>

int main()
{
    nsimd::pack<float> f(42.0f);
    nsimd::pack<float> f2 = nsimd::shr(f2, 1);

    std::cout << f2 << std::endl;

    return 0;
}

Is there something I'm doing wrong?

Expected behavior

Essentially I wish to change a simd vector, say [1, 2, 3, 4] to look like [0,1,2,3] using the right shift operation.

[gquintin]

Hi NK-Nikunj,

The error you are facing is the expected behavior of NSIMD. Let me give you details: the shr, shl and shra operators work on integer types only (hence the error) and work element-wise. I mean that

v = [1 ; 2 ; 3 ; 4]
v << n == [1 << n ; 2 << n ; 3 << n ; 4 << n]

From what you describe, what you want is a shuffle but we do not have this one yet. Moreover I have questions for you on what you want exactly :

• Do you want this shuffle to work on a 4-elements basis i mean given v = [1 ; 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ]:

  shuffle(v, 1) = [ 2 ; 3 ; 4 ; 1 ; 6 ; 7 ; 8 ; 5 ]
  

  or

  shuffle(v, 1) = [ 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ; 1 ]
  

  ?

• Do you want it only a 4-elements SIMD vectors? Do your algorithm have this constraint? Do you want it to be length agnostic?

I am asking you these according to #8, there are two ways to have shuffles length angostic.

[NK-Nikunj]

@gquintin I want it to be length agnostic. My apologies, I should've seen this comment before.