cpp/src/parquet/level_comparison_inc.h

// Licensed to the Apache Software Foundation (ASF) under one
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// distributed with this work for additional information
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// to you under the Apache License, Version 2.0 (the
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// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
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// specific language governing permissions and limitations
// under the License.
#pragma once

#include "arrow/util/bit_util.h"
#include "arrow/util/endian.h"
#include "parquet/level_comparison.h"

// Used to make sure ODR rule isn't violated.
#ifndef PARQUET_IMPL_NAMESPACE
#  error "PARQUET_IMPL_NAMESPACE must be defined"
#endif
namespace parquet::internal::PARQUET_IMPL_NAMESPACE {
/// Builds a bitmap by applying predicate to the level vector provided.
///
/// \param[in] levels Rep or def level array.
/// \param[in] num_levels The number of levels to process (must be [0, 64])
/// \param[in] predicate The predicate to apply (must have the signature `bool
/// predicate(int16_t)`.
/// \returns The bitmap using least significant "bit" ordering.
///
template <typename Predicate>
inline uint64_t LevelsToBitmap(const int16_t* levels, int64_t num_levels,
                               Predicate predicate) {
  // Both clang and GCC can vectorize this automatically with SSE4/AVX2.
  uint64_t mask = 0;
  for (int x = 0; x < num_levels; x++) {
    mask |= static_cast<uint64_t>(predicate(levels[x]) ? 1 : 0) << x;
  }
  return ::arrow::bit_util::ToLittleEndian(mask);
}

inline MinMax FindMinMaxImpl(const int16_t* levels, int64_t num_levels) {
  MinMax out{std::numeric_limits<int16_t>::max(), std::numeric_limits<int16_t>::min()};
  for (int x = 0; x < num_levels; x++) {
    out.min = std::min(levels[x], out.min);
    out.max = std::max(levels[x], out.max);
  }
  return out;
}

inline uint64_t GreaterThanBitmapImpl(const int16_t* levels, int64_t num_levels,
                                      int16_t rhs) {
  return LevelsToBitmap(levels, num_levels, [rhs](int16_t value) { return value > rhs; });
}

}  // namespace parquet::internal::PARQUET_IMPL_NAMESPACE