Use SIMD Everywhere to port code to Arm

SIMD Everywhere

SIMD Everywhere (SIMDe) is another way to get C/C++ applications with intrinsics running on Arm.

Like sse2neon it is a header-only library which makes porting code to other architectures easy.

If the code being migrated has MMX or SSE code then either sse2neon or SIMDe can be used, but if it contains AVX then SIMDe is needed.

Porting with SIMD Everywhere

To make the example application compile and run on Arm there are four steps:

• Identify the appropriate header file from SIMDe (use the table in the SIMDEverywhere wiki to find the right portable header)
• Define SIMDE_ENABLE_NATIVE_ALIASES macro before the include to enable original _mm intrinsics to be recognized
• Replace the x86-specific header file with the SIMDe one to map the intrinsics to NEON instructions
• Change the g++ compiler flags for the Arm architecture

The appropriate header file for emmintrin.h is simde/x86/sse2.h

Here is the new code (neon.cpp). The only change is related to the include files, and the definition of SIMDE_ENABLE_NATIVE_ALIASES.

    

        
        
#include <iostream>

#define SIMDE_ENABLE_NATIVE_ALIASES

#if defined(__SSE2__) || defined(__aarch64__)
  #include "simde/x86/sse2.h"
#else
  #warning SSE2/NEON support is not available. Code will not compile.
#endif

int main(int argc, char **argv)
{
    __m128 a = _mm_set_ps(4.0, 3.0, 2.0, 1.0);
    __m128 b = _mm_set_ps(8.0, 7.0, 6.0, 5.0);

    __m128 c = _mm_add_ps(a, b);

    float d[4];
    _mm_storeu_ps(d, c);

    std::cout << "result equals " << d[0] << "," << d[1]
              << "," << d[2] << "," << d[3] << std::endl;

    return 0;
}

    

This can be compiled and run on your Arm instance using the commands below.

Install wget, git, and g++ compiler, and use appropriate g++ command options:

    

        
        
sudo apt install -y git g++ wget
git clone https://github.com/simd-everywhere/simde.git
g++ -O2 -I simde/ -march=armv8.2-a+fp16+rcpc+dotprod+crypto --std=c++14 neon.cpp -o neon

    

Run the code:

    

        
        
./neon

    

and observe the output:

    

        
        result equals 6,8,10,12

        
    

Further reading

For more information on the use of SIMDe, see the below blog.

• Porting to Arm Intrinsics with SIMDe