void Engine::Shift::Multiply()

in gemmology.h [1301:1353]

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

void Engine<Arch>::Shift::Multiply(const uint8_t *A, const int8_t *B,
                                   size_t A_rows, size_t width, size_t B_cols,
                                   Callback callback, ExecutionEngine& engine) {

  using batch8 = xsimd::batch<int8_t, Arch>;
  using ubatch8 = xsimd::batch<uint8_t, Arch>;
  using batch32 = xsimd::batch<int32_t, Arch>;

  engine(0, B_cols, 8, [A, B, A_rows, width, B_cols, &callback](size_t B0_colidx) {
    const size_t simd_width = width / batch8::size;
    const auto *B0_col =
        reinterpret_cast<const batch8 *>(B) + simd_width * B0_colidx;
    /* Process one row of A at a time.  Doesn't seem to be faster to do multiple
     * rows of A at once.*/
    for (size_t A_rowidx = 0; A_rowidx < A_rows; ++A_rowidx) {
      const auto *A_row =
          reinterpret_cast<const ubatch8 *>(A + A_rowidx * width);
      /* These will be packed 16-bit integers containing sums for each row of B
         multiplied by the row of A. Iterate over shared (inner) dimension.*/
      /* Upcast to 32-bit and horizontally add. Seems a bit faster if this is
       * declared here.*/
      size_t k = 0;
      ubatch8 a = *(A_row + k);
      batch32 isum0 = maddw(a, *(B0_col + k * 8));
      batch32 isum1 = maddw(a, *(B0_col + k * 8 + 1));
      batch32 isum2 = maddw(a, *(B0_col + k * 8 + 2));
      batch32 isum3 = maddw(a, *(B0_col + k * 8 + 3));
      batch32 isum4 = maddw(a, *(B0_col + k * 8 + 4));
      batch32 isum5 = maddw(a, *(B0_col + k * 8 + 5));
      batch32 isum6 = maddw(a, *(B0_col + k * 8 + 6));
      batch32 isum7 = maddw(a, *(B0_col + k * 8 + 7));
      for (k = 1; k < simd_width; ++k) {
        a = *(A_row + k);
        /* Multiply 8-bit, horizontally add to packed 16-bit integers.*/
        /* Upcast to 32-bit and horizontally add.*/
        isum0 = maddw(a, *(B0_col + k * 8 + 0), isum0);
        isum1 = maddw(a, *(B0_col + k * 8 + 1), isum1);
        isum2 = maddw(a, *(B0_col + k * 8 + 2), isum2);
        isum3 = maddw(a, *(B0_col + k * 8 + 3), isum3);
        isum4 = maddw(a, *(B0_col + k * 8 + 4), isum4);
        isum5 = maddw(a, *(B0_col + k * 8 + 5), isum5);
        isum6 = maddw(a, *(B0_col + k * 8 + 6), isum6);
        isum7 = maddw(a, *(B0_col + k * 8 + 7), isum7);
      }
      /* Reduce sums within 128-bit lanes.*/
      auto pack0123 = Pack0123(isum0, isum1, isum2, isum3);
      auto pack4567 = Pack0123(isum4, isum5, isum6, isum7);
      /*The specific implementation may need to reduce further.*/
      auto total = PermuteSummer(pack0123, pack4567);
      callback(total, A_rowidx, B0_colidx, B_cols);
    }
  });
}