ceph/src/arrow/cpp/src/arrow/util/bitmap_generate.h

   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 #pragma once
  19
  20 #include <cstdint>
  21 #include <memory>
  22
  23 #include "arrow/buffer.h"
  24 #include "arrow/memory_pool.h"
  25 #include "arrow/result.h"
  26 #include "arrow/util/bit_util.h"
  27 #include "arrow/util/visibility.h"
  28
  29 namespace arrow {
  30 namespace internal {
  31
  32 // A std::generate() like function to write sequential bits into a bitmap area.
  33 // Bits preceding the bitmap area are preserved, bits following the bitmap
  34 // area may be clobbered.
  35
  36 template <class Generator>
  37 void GenerateBits(uint8_t* bitmap, int64_t start_offset, int64_t length, Generator&& g) {
  38   if (length == 0) {
  39     return;
  40   }
  41   uint8_t* cur = bitmap + start_offset / 8;
  42   uint8_t bit_mask = BitUtil::kBitmask[start_offset % 8];
  43   uint8_t current_byte = *cur & BitUtil::kPrecedingBitmask[start_offset % 8];
  44
  45   for (int64_t index = 0; index < length; ++index) {
  46     const bool bit = g();
  47     current_byte = bit ? (current_byte | bit_mask) : current_byte;
  48     bit_mask = static_cast<uint8_t>(bit_mask << 1);
  49     if (bit_mask == 0) {
  50       bit_mask = 1;
  51       *cur++ = current_byte;
  52       current_byte = 0;
  53     }
  54   }
  55   if (bit_mask != 1) {
  56     *cur++ = current_byte;
  57   }
  58 }
  59
  60 // Like GenerateBits(), but unrolls its main loop for higher performance.
  61
  62 template <class Generator>
  63 void GenerateBitsUnrolled(uint8_t* bitmap, int64_t start_offset, int64_t length,
  64                           Generator&& g) {
  65   static_assert(std::is_same<decltype(std::declval<Generator>()()), bool>::value,
  66                 "Functor passed to GenerateBitsUnrolled must return bool");
  67
  68   if (length == 0) {
  69     return;
  70   }
  71   uint8_t current_byte;
  72   uint8_t* cur = bitmap + start_offset / 8;
  73   const uint64_t start_bit_offset = start_offset % 8;
  74   uint8_t bit_mask = BitUtil::kBitmask[start_bit_offset];
  75   int64_t remaining = length;
  76
  77   if (bit_mask != 0x01) {
  78     current_byte = *cur & BitUtil::kPrecedingBitmask[start_bit_offset];
  79     while (bit_mask != 0 && remaining > 0) {
  80       current_byte |= g() * bit_mask;
  81       bit_mask = static_cast<uint8_t>(bit_mask << 1);
  82       --remaining;
  83     }
  84     *cur++ = current_byte;
  85   }
  86
  87   int64_t remaining_bytes = remaining / 8;
  88   uint8_t out_results[8];
  89   while (remaining_bytes-- > 0) {
  90     for (int i = 0; i < 8; ++i) {
  91       out_results[i] = g();
  92     }
  93     *cur++ = (out_results[0] | out_results[1] << 1 | out_results[2] << 2 |
  94               out_results[3] << 3 | out_results[4] << 4 | out_results[5] << 5 |
  95               out_results[6] << 6 | out_results[7] << 7);
  96   }
  97
  98   int64_t remaining_bits = remaining % 8;
  99   if (remaining_bits) {
 100     current_byte = 0;
 101     bit_mask = 0x01;
 102     while (remaining_bits-- > 0) {
 103       current_byte |= g() * bit_mask;
 104       bit_mask = static_cast<uint8_t>(bit_mask << 1);
 105     }
 106     *cur++ = current_byte;
 107   }
 108 }
 109
 110 }  // namespace internal
 111 }  // namespace arrow