histogram.cu

#include <iostream>
#include <string>
#include <thrust/device_vector.h>
#include <thrust/sort.h>
#include <thrust/sequence.h>

void print_array(const thrust::device_vector<int>& val,
                 const std::string tag,
                 const int size) {
  std::cout << tag;
  std::cout << " = {";
  for (int i = 0; i < size - 1; i++) {
    std::cout << val[i] << ", ";
  }
  std::cout << val[size - 1] << "}\n";
}

int main() {
  const int key[] {1, 1, 2, 2, 2, 3, 3, 1, 1};
  const int value[] {1, 1, 1, 1, 1, 1, 1, 1, 1};
  const int in_size = sizeof(key) / sizeof(int);

  // reduce_by_key test
  thrust::device_vector<int> key_in(key, key + in_size);
  thrust::device_vector<int> value_in(value, value + in_size);
  thrust::device_vector<int> key_out(in_size, 0);
  thrust::device_vector<int> value_out(in_size, 0);

  auto new_end = thrust::reduce_by_key(key_in.begin(),
                                       key_in.end(),
                                       value_in.begin(),
                                       key_out.begin(),
                                       value_out.begin());
  int out_size = new_end.second - value_out.begin();

  std::cout << "reduce_by_key test\n";
  std::cout << "input:\n";
  print_array(key_in, "key  ", in_size);
  print_array(value_in, "value", in_size);
  std::cout << "output:\n";
  print_array(key_out, "key  ", out_size);
  print_array(value_out, "value", out_size);
  std::cout << "\n";

  // histogram
  thrust::device_vector<int> uni_vect(in_size, 1);
  thrust::device_vector<int> num_in_bins(in_size);
  thrust::sort(key_in.begin(), key_in.end());
  new_end = thrust::reduce_by_key(key_in.begin(),
                                  key_in.end(),
                                  uni_vect.begin(),
                                  key_out.begin(),
                                  num_in_bins.begin());
  out_size = new_end.second - num_in_bins.begin();
  std::cout << "histogram test\n";
  std::cout << "input:\n";
  print_array(key_in, "key", in_size);
  std::cout << "output:\n";
  print_array(key_out,     "key          ", out_size);
  print_array(num_in_bins, "number in bin", out_size);
  std::cout << "\n";

  // get histogram pointer
  thrust::device_vector<int> pointer(out_size + 1, 0);
  thrust::inclusive_scan(num_in_bins.begin(),
                         num_in_bins.end(),
                         pointer.begin() + 1);
  std::cout << "histogram pointer\n";
  print_array(pointer, "pointer", pointer.size());
  std::cout << "\n";
}