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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. using namespace std;
  5.  
  6. #if 1
  7.     #ifdef _MSC_VER
  8.         #define NO_INLINE __declspec(noinline)
  9.     #else
  10.         #define NO_INLINE __attribute__((noinline))
  11.     #endif
  12. #else
  13.     #define NO_INLINE
  14. #endif
  15.  
  16. void use(void *p)
  17. {
  18.     static auto volatile t=p;
  19. };
  20.  
  21. template<typename T,unsigned N,typename F>
  22. NO_INLINE auto cps_alloca_static(F &&f) -> decltype(f(nullptr))
  23. {
  24.     T data[N];
  25.     return f(&data[0]);
  26. }
  27.  
  28. template<typename T,typename F>
  29. NO_INLINE auto cps_alloca_dynamic(unsigned n,F &&f) -> decltype(f(nullptr))
  30. {
  31.     vector<T> data(n);
  32.     return f(&data[0]);
  33. }
  34.  
  35. template<typename T,typename F>
  36. auto cps_alloca(unsigned n,F &&f) -> decltype(f(nullptr))
  37. {
  38.     switch(n)
  39.     {
  40.         case 1: return cps_alloca_static<T,1>(f);
  41.         case 2: return cps_alloca_static<T,2>(f);
  42.         case 3: return cps_alloca_static<T,3>(f);
  43.         case 4: return cps_alloca_static<T,4>(f);
  44.         default: return cps_alloca_dynamic<T>(n,f);
  45.     }; // mpl::for_each / array / index pack / recursive bsearch / etc variación
  46. }
  47.  
  48. struct Payload
  49. {
  50.     volatile char d[2048];
  51. };
  52.  
  53. void test(unsigned n)
  54. {
  55.     volatile char begin;
  56.     cps_alloca<Payload>(n,[&](Payload *p)
  57.     {
  58.         volatile char end;
  59.         const auto overhead = &begin-&end - int(n*sizeof(Payload));
  60.         cout << "n=" << n << "\toverhead=" << overhead << endl;
  61.         use(p);
  62.     });
  63. }
  64.  
  65. int main()
  66. {
  67.     for(auto i=1u;i!=6u;++i)
  68.         test(i);
  69. }
Success #stdin #stdout 0s 3032KB
comments (?)
stdin 
Standard input is empty
stdout 
n=1	overhead=24
n=2	overhead=24
n=3	overhead=24
n=4	overhead=24
n=5	overhead=-10200
https://ideone.com/xBY8S6
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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