// Copyright 2023 PingCAP, Inc.
//
// Licensed 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 <Common/PODArray.h>
#include <common/types.h>

namespace DB
{
/// It's a class which represents the result of weak and fast hash function per row in column.
/// It's usually hardware accelerated CRC32-C.
/// Has function result may be combined to calculate hash for tuples.
///
/// The main purpose why this class needed is to support data initialization. Initially, every bit is 1.
class WeakHash32
{
public:
    using Container = PaddedPODArray<UInt32>;

    static constexpr UInt32 initial_hash = ~UInt32(0);

    explicit WeakHash32(size_t size)
        : data(size, initial_hash)
    {}
    WeakHash32(const WeakHash32 & other) { data.assign(other.data); }

    void reset(size_t size) { data.assign(size, initial_hash); }

    const Container & getData() const { return data; }
    Container & getData() { return data; }

private:
    PaddedPODArray<UInt32> data;
};

} // namespace DB