fs/range-split-vi.h

/*
Copyright 2022 The Photon Authors

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 <cinttypes>
#include <cassert>
#include <algorithm>
#include <photon/fs/range-split.h>

// 本文件主打（文件偏移量）区间的分解操作，支持不固定间隔（struct range_split_vi）

namespace photon {
namespace fs
{
    // variable interval
    struct range_split_vi : public basic_range_split<range_split_vi>
    {
        const uint64_t* key_points;
        uint64_t n;

        // the `key_points` are composed of `n` (at least 3) ascending points (offsets),
        // begining with 0, and ending with UINT64_MAX !!
        range_split_vi(uint64_t offset, uint64_t length, const uint64_t* key_points, uint64_t n) :
            key_points(key_points), n(n)
        {
            assert(n >= 3);
            assert(key_points[0] == 0);
            assert(key_points[n-1] == UINT64_MAX);
            assert(ascending(key_points, n));
            init(offset, length);
        }
        bool ascending(const uint64_t* key_points, uint64_t n) const
        {
            for (uint64_t i = 1; i < n; ++i)
                if (key_points[i] <= key_points[i-1])
                    return false;
            return true;
        }
        void divide(uint64_t x, uint64_t& round_down, uint64_t& remainder,
                    uint64_t& round_up) const
        {
            auto ptr = std::upper_bound(key_points, key_points + n, x);
            assert(ptr > key_points);
            assert(ptr[-1] <= x && x < ptr[0]);
            auto i = ptr - key_points;
            round_down = i - 1;
            remainder = x - ptr[-1];
            round_up = (remainder > 0 ? i : round_down);
        }
        uint64_t multiply(uint64_t i, uint64_t x) const
        {
            return key_points[i] + x;
        }
        uint64_t get_length(uint64_t i) const
        {
            assert(i < n - 1);
            return key_points[i+1] - key_points[i];
        }
    };
}
}