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// Licensed to the Apache Software Foundation (ASF) under one
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// or more contributor license agreements. See the NOTICE file
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// distributed with this work for additional information
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// regarding copyright ownership. The ASF licenses this file
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// to you under the Apache License, Version 2.0 (the
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// "License"); you may not use this file except in compliance
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// with the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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#pragma once
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#include <algorithm>
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#include "arrow/util/bit_util.h"
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namespace arrow {
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namespace internal {
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struct BitmapWordAlignParams {
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int64_t leading_bits;
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int64_t trailing_bits;
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int64_t trailing_bit_offset;
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const uint8_t* aligned_start;
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int64_t aligned_bits;
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int64_t aligned_words;
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};
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// Compute parameters for accessing a bitmap using aligned word instructions.
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// The returned parameters describe:
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// - a leading area of size `leading_bits` before the aligned words
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// - a word-aligned area of size `aligned_bits`
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// - a trailing area of size `trailing_bits` after the aligned words
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template <uint64_t ALIGN_IN_BYTES>
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inline BitmapWordAlignParams BitmapWordAlign(const uint8_t* data, int64_t bit_offset,
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int64_t length) {
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static_assert(bit_util::IsPowerOf2(ALIGN_IN_BYTES),
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"ALIGN_IN_BYTES should be a positive power of two");
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constexpr uint64_t ALIGN_IN_BITS = ALIGN_IN_BYTES * 8;
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BitmapWordAlignParams p;
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// Compute a "bit address" that we can align up to ALIGN_IN_BITS.
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// We don't care about losing the upper bits since we are only interested in the
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// difference between both addresses.
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const uint64_t bit_addr =
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reinterpret_cast<size_t>(data) * 8 + static_cast<uint64_t>(bit_offset);
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const uint64_t aligned_bit_addr = bit_util::RoundUpToPowerOf2(bit_addr, ALIGN_IN_BITS);
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p.leading_bits = std::min<int64_t>(length, aligned_bit_addr - bit_addr);
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p.aligned_words = (length - p.leading_bits) / ALIGN_IN_BITS;
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p.aligned_bits = p.aligned_words * ALIGN_IN_BITS;
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p.trailing_bits = length - p.leading_bits - p.aligned_bits;
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p.trailing_bit_offset = bit_offset + p.leading_bits + p.aligned_bits;
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p.aligned_start = data + (bit_offset + p.leading_bits) / 8;
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return p;
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}
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} // namespace internal
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} // namespace arrow
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