Add decode offset avx2

cpp/src/arrow/acero/swiss_join_avx2.cc

@@ -362,6 +362,25 @@ inline void Decode1_avx2(uint8_t* output, const uint8_t* row_ptr, uint32_t num_b
  }
 }
 
+inline uint32_t Decode8Offset_avx2(uint32_t* output, uint32_t current_length,
+ __m256i num_bytes) {
+ uint32_t num_bytes_last = static_cast<uint32_t>(_mm256_extract_epi32(num_bytes, 7));
+ // Init every offset with the current length.
+ __m256i offsets = _mm256_set1_epi32(current_length);
+ // We keep right-shifting the length and accumulate the offset by adding the length.
+ __m256i length =
+ _mm256_permutevar8x32_epi32(num_bytes, _mm256_setr_epi32(7, 0, 1, 2, 3, 4, 5, 6));
+ length = _mm256_insert_epi32(length, 0, 0);
+ for (int i = 0; i < 7; ++i) {
+ offsets = _mm256_add_epi32(offsets, length);
+ length =
+ _mm256_permutevar8x32_epi32(length, _mm256_setr_epi32(7, 0, 1, 2, 3, 4, 5, 6));
+ length = _mm256_insert_epi32(length, 0, 0);
+ }
+ _mm256_storeu_si256(reinterpret_cast<__m256i*>(output), offsets);
+ return _mm256_extract_epi32(offsets, 7) + num_bytes_last;
+}
+
 inline void Decode8Null_avx2(uint8_t* output, uint64_t null_bytes) {
  uint8_t null_bits =
  static_cast<uint8_t>(_mm256_movemask_epi8(_mm256_set1_epi64x(null_bytes)));
@@ -446,8 +465,17 @@ int RowArray::DecodeFixedLength_avx2(ResizableArrayData* output, int output_star
 int RowArray::DecodeOffsets_avx2(ResizableArrayData* output, int output_start_row,
  int column_id, int num_rows_to_append,
  const uint32_t* row_ids) const {
- DecodeOffsets(output, output_start_row, column_id, num_rows_to_append, row_ids);
- return num_rows_to_append;
+ uint32_t* offsets =
+ reinterpret_cast<uint32_t*>(output->mutable_data(1)) + output_start_row;
+ uint32_t current_length = (output_start_row == 0) ? 0 : offsets[0];
+ int num_rows_processed = RowArrayAccessor::Visit_avx2(
+ rows_, column_id, num_rows_to_append, row_ids,
+ [&](int i, const uint8_t* row_ptr_base, __m256i offset_lo, __m256i offset_hi,
+ __m256i num_bytes) {
+ current_length = Decode8Offset_avx2(offsets + i, current_length, num_bytes);
+ });
+ offsets[num_rows_processed] = current_length;
+ return num_rows_processed;
 }
 
 int RowArray::DecodeVarLength_avx2(ResizableArrayData* output, int output_start_row,