// Licensed to the Apache Software Foundation (ASF) under one

// or more contributor license agreements.  See the NOTICE file

// distributed with this work for additional information

// regarding copyright ownership.  The ASF licenses this file

// to you under the Apache License, Version 2.0 (the

// "License"); you may not use this file except in compliance

// 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

// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY

// KIND, either express or implied.  See the License for the

// specific language governing permissions and limitations

// under the License.

#pragma once

#include <cstdint>

#include <cstring>

#include "common/compiler_util.h"

#include "util/simd/bits.h"

namespace doris::simd {

#if defined(__x86_64__)

namespace detail {

struct alignas(16) SelectionLookupTable {

    uint16_t positions[256][8] {};

    uint8_t counts[256] {};

    constexpr SelectionLookupTable() {

        for (unsigned mask = 0; mask < 256; ++mask) {

            for (unsigned bit = 0; bit < 8; ++bit) {

                if (mask & (1U << bit)) {

                    positions[mask][counts[mask]++] = static_cast<uint16_t>(bit);

                }

            }

        }

    }

};

inline constexpr SelectionLookupTable SELECTION_LOOKUP_TABLE;

} // namespace detail

#endif

// Append base + bit positions in ascending order. The caller must provide room for

// bits_mask_length() entries, and base + bits_mask_length() - 1 must fit in uint16_t.

// Only the returned number of entries are valid; the lookup path can write extra entries.

ALWAYS_INLINE inline uint16_t append_selected_indices(

        decltype(bytes_mask_to_bits_mask(nullptr)) mask, uint16_t base, uint16_t* output) {

    uint16_t count = 0;

#if defined(__x86_64__)

    for (unsigned offset = 0; offset < 32; offset += 8) {

        const auto part = static_cast<uint8_t>(mask >> offset);

        uint16_t indices[8];

        for (unsigned lane = 0; lane < 8; ++lane) {

            indices[lane] = static_cast<uint16_t>(

                    base + offset + detail::SELECTION_LOOKUP_TABLE.positions[part][lane]);

        }

        // count <= offset, so the fixed-width store stays within 32 output entries.

        std::memcpy(output + count, indices, sizeof(indices));

        count += detail::SELECTION_LOOKUP_TABLE.counts[part];

    }

#else

    iterate_through_bits_mask(

            [&](const int bit_pos) { output[count++] = base + static_cast<uint16_t>(bit_pos); },

            mask);

#endif

    return count;

}

} // namespace doris::simd