inline __m512 Concat()

in gemmology.h [732:735]

• 3 lines of code
• 1 McCabe index (conditional complexity)

inline __m512 Concat(const __m256 first, const __m256 second) {
  // INTGEMM_AVX512DQ but that goes with INTGEMM_AVX512BW anyway.
  return _mm512_insertf32x8(_mm512_castps256_ps512(first), second, 1);
}