ceph/src/arrow/cpp/src/arrow/util/bit_run_reader.cc

   1 // Licensed to the Apache Software Foundation (ASF) under one
   2 // or more contributor license agreements.  See the NOTICE file
   3 // distributed with this work for additional information
   4 // regarding copyright ownership.  The ASF licenses this file
   5 // to you under the Apache License, Version 2.0 (the
   6 // "License"); you may not use this file except in compliance
   7 // with the License.  You may obtain a copy of the License at
   8 //
   9 //   http://www.apache.org/licenses/LICENSE-2.0
  10 //
  11 // Unless required by applicable law or agreed to in writing,
  12 // software distributed under the License is distributed on an
  13 // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14 // KIND, either express or implied.  See the License for the
  15 // specific language governing permissions and limitations
  16 // under the License.
  17
  18 #include "arrow/util/bit_run_reader.h"
  19
  20 #include <cstdint>
  21
  22 #include "arrow/util/bit_util.h"
  23
  24 namespace arrow {
  25 namespace internal {
  26
  27 #if ARROW_LITTLE_ENDIAN
  28
  29 BitRunReader::BitRunReader(const uint8_t* bitmap, int64_t start_offset, int64_t length)
  30     : bitmap_(bitmap + (start_offset / 8)),
  31       position_(start_offset % 8),
  32       length_(position_ + length) {
  33   if (ARROW_PREDICT_FALSE(length == 0)) {
  34     word_ = 0;
  35     return;
  36   }
  37
  38   // On the initial load if there is an offset we need to account for this when
  39   // loading bytes.  Every other call to LoadWord() should only occur when
  40   // position_ is a multiple of 64.
  41   current_run_bit_set_ = !BitUtil::GetBit(bitmap, start_offset);
  42   int64_t bits_remaining = length + position_;
  43
  44   LoadWord(bits_remaining);
  45
  46   // Prepare for inversion in NextRun.
  47   // Clear out any preceding bits.
  48   word_ = word_ & ~BitUtil::LeastSignificantBitMask(position_);
  49 }
  50
  51 #endif
  52
  53 }  // namespace internal
  54 }  // namespace arrow