neighbor_list.h

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#pragma once
 
#include <vector>
#include<iostream>
#include <cmath>
#include <cassert>
 
class PageAllocator {
public:
    struct Page {
        std::vector<int> data;
        int capacity;
        int offset;
    };
 
    std::vector<Page> pages;
    int pgsize;
 
    static constexpr int DEFAULT_PGSIZE = 1024;
 
    // Default constructor
    PageAllocator() : pgsize(DEFAULT_PGSIZE) {
        if (pgsize > 0) new_page();
    }
 
    PageAllocator(int pgsize_) : pgsize(pgsize_) {
        new_page();
    }
 
    ~PageAllocator() {
        // no manual delete[]; vectors clean themselves
    }
 
    PageAllocator(const PageAllocator&) = delete;
    PageAllocator& operator=(const PageAllocator&) = delete;
 
    // Allow move
    PageAllocator(PageAllocator&&) = default;
    PageAllocator& operator=(PageAllocator&&) = default;
 
    void new_page() {
        Page p;
        p.capacity = pgsize;
        p.offset = 0;
        p.data.resize(pgsize);
        pages.push_back(std::move(p));
    }
 
    int* allocate(int n) {
        if (n <= 0) return nullptr;
        // reject requests larger than a single page
        if (n > pgsize) {
            std::cerr << "PageAllocator::allocate error: request " << n << " larger than page size " << pgsize << std::endl;
            return nullptr;
        }
        if (pages.empty()) new_page();
        Page& p = pages.back();
        if (p.offset + n > p.capacity) {
            new_page();
            return allocate(n);
        }
        int* ptr = p.data.data() + p.offset;
        p.offset += n;
        return ptr;
    }
 
    void reset() {
        pages.resize(1);
        pages[0].offset = 0;
    }
};
 
// Neighbor List
 
class NeighborList {
public:
    NeighborList() = default;
    ~NeighborList() = default;
 
    int nlocal;
 
    std::vector<int> numneigh;
    std::vector<int*> firstneigh;
 
    PageAllocator allocator;
 
    void initialize(int n, int pgsize) {
        nlocal = n;
    allocator = PageAllocator(pgsize);
    // ensure neighbor containers are sized and initialized
    numneigh.assign(n, 0);
    firstneigh.assign(n, nullptr);
    }
 
    void reset() {
        allocator.reset();
    }
};