How to use libsimdpp?

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I have some problems.
I try to convert standard SIMD instructions to other using libsimdpp.
libsimdpp is a portable header-only zero-overhead C++ wrapper around single-instruction multiple-data (SIMD) intrinsics found in many compilers.https://github.com/p12tic/libsimdpp[^]

C++

__m128i v_zero = _mm_setzero_si128();
  for ( ; j <= width - 8; j += 8)
  {
       __m128i v_dx = _mm_loadu_si128((const __m128i *)(_dx + j));
       __m128i v_dy = _mm_loadu_si128((const __m128i *)(_dy + j));
       v_dx = _mm_max_epi16(v_dx, _mm_sub_epi16(v_zero, v_dx));
       v_dy = _mm_max_epi16(v_dy, _mm_sub_epi16(v_zero, v_dy));

       __m128i v_norm = _mm_add_epi32(_mm_unpacklo_epi16(v_dx, v_zero), _mm_unpacklo_epi16(v_dy, v_zero));
       _mm_storeu_si128((__m128i *)(_norm + j), v_norm);

       v_norm = _mm_add_epi32(_mm_unpackhi_epi16(v_dx, v_zero), _mm_unpackhi_epi16(v_dy, v_zero));
      _mm_storeu_si128((__m128i *)(_norm + j + 4), v_norm);
}

this code is using standard simd intrinsics.

How to write this code using libsimdpp?

Thanks

Posted 28-Jan-15 23:07pm

Member 11302981

Updated 28-Jan-15 23:11pm

v2

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[no name] 29-Jan-15 12:47pm

You can read through the source code.

Start with the test code. Look at ...

https://github.com/p12tic/libsimdpp/blob/master/test/utils/test_helpers.h

https://github.com/p12tic/libsimdpp/blob/master/test/insn/math_int.cc

In particular, look at the code following this comment in math_int.cc:

| // Vectors with 16-bit integer elements

I am puzzled by this statement:

| v_dx = _mm_max_epi16(v_dx, _mm_sub_epi16(v_zero, v_dx));

This looks to be v_dx = max(v_dx, -v_dx) ... which would be v_dx. Seems like nonsense.

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