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  1. #include <algorithm>
  2. #include <cassert>
  3. #include <initializer_list>
  4. #include <iostream>
  5. #include <iterator>
  6. #include <memory>
  7. #include <vector>
  8.  
  9. using namespace std;
  10.  
  11. // All the JointPool / JointAllocator code would be 'library' code in practice and should be
  12. // compared to the code required to implement joint allocation in the compiler. Once the library
  13. // code is written it can be used fairly simply as demonstrated in the 'Usage' section below.
  14.  
  15. template <typename T>
  16. struct JointPoolSizeTraits;
  17.  
  18. struct JointPool {
  19.     explicit JointPool(size_t totalBytes)
  20.         : m_jointBegin(new char[totalBytes]),
  21.           m_jointCurrent(m_jointBegin.get()),
  22.           m_jointEnd(m_jointBegin.get() + totalBytes) {}
  23.     unique_ptr<char[]> m_jointBegin;
  24.     char* m_jointCurrent = nullptr;
  25.     char* m_jointEnd = nullptr;
  26.  
  27.     void* allocate(size_t bytes) {
  28.         if (m_jointCurrent + bytes <= m_jointEnd) {
  29.             auto p = m_jointCurrent;
  30.             m_jointCurrent += bytes;
  31.             return p;
  32.         }
  33.         assert(false);
  34.         return nullptr;
  35.     }
  36. };
  37.  
  38. template <typename... Ts>
  39. size_t GetJointPoolSize() {
  40.     return 0;
  41. }
  42.  
  43. template <typename T, typename... Ts, typename U, typename... Us>
  44. size_t GetJointPoolSize(U&& arg, Us&&... args) {
  45.     return JointPoolSizeTraits<T>::size(arg) + GetJointPoolSize<Ts...>(args...);
  46. }
  47.  
  48. template <class T>
  49. struct JointAllocator {
  50.     typedef T value_type;
  51.  
  52.     JointAllocator(JointPool* pool) : m_pool(pool) {}
  53.     JointAllocator(const JointAllocator&) = default;
  54.  
  55.     template <class U>
  56.     JointAllocator(const JointAllocator<U>& other)
  57.         : m_pool(other.m_pool) {}
  58.  
  59.     T* allocate(std::size_t n) { return reinterpret_cast<T*>(m_pool->allocate(n * sizeof(T))); }
  60.     void deallocate(T* p, std::size_t n) {}
  61.  
  62.     JointPool* m_pool = nullptr;
  63. };
  64.  
  65. template <typename T>
  66. using JointVector = vector<T, JointAllocator<T>>;
  67.  
  68. template <typename T>
  69. struct JointPoolSizeTraits<JointVector<T>> {
  70.     static constexpr size_t size(size_t n) { return sizeof(T*) + sizeof(T) * n; }
  71. };
  72.  
  73. // Usage - with library support for joint allocation, usage might look something like this:
  74.  
  75. struct Vector3 {
  76.     float x, y, z;
  77. };
  78.  
  79. struct Mesh {
  80. private:
  81.     JointPool pool;
  82.  
  83. public:
  84.     template <typename ItPs, typename ItIs>
  85.     Mesh(ItPs firstP, ItPs lastP, ItIs firstI, ItIs lastI)
  86.         : pool(GetJointPoolSize<decltype(positions), decltype(indices)>(distance(firstP, lastP),
  87.                                                                         distance(firstI, lastI))),
  88.           positions(firstP, lastP, &pool),
  89.           indices(firstI, lastI, &pool) {}
  90.  
  91.     Mesh(initializer_list<Vector3> ps, initializer_list<int> is)
  92.         : Mesh(begin(ps), end(ps), begin(is), end(is)) {}
  93.  
  94.     JointVector<Vector3> positions;
  95.     JointVector<int> indices;
  96. };
  97.  
  98. ostream& operator<<(ostream& os, const Mesh& m) {
  99.     for (const auto& pos : m.positions) os << "(" << pos.x << ", " << pos.y << ", " << pos.z << "), ";
  100.     for (const auto& index : m.indices) os << index << ", ";
  101.     return os << endl;
  102. }
  103.  
  104. int main() {
  105.     // initialize a Mesh with explicit verts and indices
  106.     Mesh myMesh{{{0.f, 0.f, 0.f}, {1.0f, 0.0f, 0.0f}, {0.0f, 1.0f, 0.0f}}, {0, 1, 2}};
  107.  
  108.     // initialize a Mesh with iterator pairs
  109.     Mesh mySecondMesh{begin(myMesh.positions), end(myMesh.positions), begin(myMesh.indices),
  110.                       end(myMesh.indices)};
  111.  
  112.     cout << myMesh << mySecondMesh;
  113. }
  114.  
Success #stdin #stdout 0s 3432KB
comments (?)
stdin
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Standard input is empty
stdout
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(0, 0, 0), (1, 0, 0), (0, 1, 0), 0, 1, 2, 
(0, 0, 0), (1, 0, 0), (0, 1, 0), 0, 1, 2,
https://ideone.com/umU1UC
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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