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  1. enum {
  2.     kMaxSize = 110000000,
  3.     kMinSize = 1000000,
  4.     kRadix = 1500,
  5.     kMaxCounters = (kMaxSize + kRadix - 1) / kRadix,
  6. };
  7.  
  8. struct IndexValue
  9. {
  10.     unsigned index;
  11.     unsigned value;
  12. };
  13.  
  14. unsigned g_input[kMaxSize];
  15. unsigned g_index[kMaxSize];
  16. struct IndexValue g_sort[kMaxSize];
  17. unsigned g_counters[kMaxCounters];
  18. unsigned g_output[kMaxSize];
  19.  
  20. void reorder2(const unsigned size)
  21. {
  22.     const unsigned min_bucket = size / kRadix;
  23.     const unsigned large_buckets = size % kRadix;
  24.     g_counters[0] = 0;
  25.  
  26.     for (unsigned i = 1; i <= large_buckets; ++i)
  27.         g_counters[i] = g_counters[i - 1] + min_bucket + 1;
  28.  
  29.     for (unsigned i = large_buckets + 1; i < kRadix; ++i)
  30.         g_counters[i] = g_counters[i - 1] + min_bucket;
  31.  
  32.     for (unsigned i = 0; i < size; ++i)
  33.     {
  34.         const unsigned dst = g_counters[g_index[i] % kRadix]++;
  35.         g_sort[dst].index = g_index[i] / kRadix;
  36.         g_sort[dst].value = g_input[i];
  37.         __builtin_prefetch(&g_sort[dst + 1].value, 1);
  38.     }
  39.  
  40.     g_counters[0] = 0;
  41.  
  42.     for (unsigned i = 1; i < (size + kRadix - 1) / kRadix; ++i)
  43.         g_counters[i] = g_counters[i - 1] + kRadix;
  44.  
  45.     for (unsigned i = 0; i < size; ++i)
  46.     {
  47.         const unsigned dst = g_counters[g_sort[i].index]++;
  48.         g_output[dst] = g_sort[i].value;
  49.         __builtin_prefetch(&g_output[dst + 1], 1);
  50.     }
  51. }
  52.  
  53. void reorder1(const unsigned size)
  54. {
  55.     for (unsigned i = 0; i < size; ++i)
  56.         g_output[g_index[i]] = g_input[i];
  57. }
  58.  
  59. #include <iostream>
  60. #include <random>
  61. #include <chrono>
  62. #include <algorithm>
  63. #include <numeric>
  64. using namespace std;
  65.  
  66. int main()
  67. {
  68.     mt19937_64 rng(random_device{}());
  69.  
  70.     for (unsigned size = kMaxSize; size > kMinSize; size -= size / 4)
  71.     //for (unsigned size = 64*1024*kRadix; size > kMinSize; size -= size / 2)
  72.     {
  73.         iota(begin(g_index), begin(g_index) + size, 0);
  74.         shuffle(begin(g_index), begin(g_index) + size, rng);
  75.         copy(begin(g_index), begin(g_index) + size, begin(g_input));
  76.  
  77.         const auto start = chrono::steady_clock::now();
  78.         reorder2(size);
  79.         const chrono::nanoseconds time = chrono::steady_clock::now() - start;
  80.  
  81.         const auto b = begin(g_output);
  82.         const auto e = begin(g_output) + size;
  83.  
  84.         bool ok = adjacent_find(b, e, [&](auto l, auto r){return l + 1 != r;})
  85.                   == e;
  86.  
  87.         cout << size << ' ' << time.count() / double(size)
  88.         << ' ' << boolalpha << ok << '\n';
  89.     }
  90. }
Runtime error #stdin #stdout 0s 148KB
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https://ideone.com/Q7FlIh
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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