1 #include <thrust/host_vector.h>
2 #include <thrust/device_vector.h>
3 #include <thrust/generate.h>
4 #include <thrust/sequence.h>
5 #include <thrust/sort.h>
6 #include <thrust/gather.h>
7 #include <thrust/random.h>
8 #include <iostream>
9
10 // This example shows how to perform a lexicographical sort on multiple keys.
11 //
12 // http://en.wikipedia.org/wiki/Lexicographical_order
13
14 template <typename KeyVector, typename PermutationVector>
update_permutation(KeyVector & keys,PermutationVector & permutation)15 void update_permutation(KeyVector& keys, PermutationVector& permutation)
16 {
17 // temporary storage for keys
18 KeyVector temp(keys.size());
19
20 // permute the keys with the current reordering
21 thrust::gather(permutation.begin(), permutation.end(), keys.begin(), temp.begin());
22
23 // stable_sort the permuted keys and update the permutation
24 thrust::stable_sort_by_key(temp.begin(), temp.end(), permutation.begin());
25 }
26
27
28 template <typename KeyVector, typename PermutationVector>
apply_permutation(KeyVector & keys,PermutationVector & permutation)29 void apply_permutation(KeyVector& keys, PermutationVector& permutation)
30 {
31 // copy keys to temporary vector
32 KeyVector temp(keys.begin(), keys.end());
33
34 // permute the keys
35 thrust::gather(permutation.begin(), permutation.end(), temp.begin(), keys.begin());
36 }
37
38
random_vector(size_t N)39 thrust::host_vector<int> random_vector(size_t N)
40 {
41 thrust::host_vector<int> vec(N);
42 static thrust::default_random_engine rng;
43 static thrust::uniform_int_distribution<int> dist(0, 9);
44
45 for (size_t i = 0; i < N; i++)
46 vec[i] = dist(rng);
47
48 return vec;
49 }
50
51
main(void)52 int main(void)
53 {
54 size_t N = 20;
55
56 // generate three arrays of random values
57 thrust::device_vector<int> upper = random_vector(N);
58 thrust::device_vector<int> middle = random_vector(N);
59 thrust::device_vector<int> lower = random_vector(N);
60
61 std::cout << "Unsorted Keys" << std::endl;
62 for(size_t i = 0; i < N; i++)
63 {
64 std::cout << "(" << upper[i] << "," << middle[i] << "," << lower[i] << ")" << std::endl;
65 }
66
67 // initialize permutation to [0, 1, 2, ... ,N-1]
68 thrust::device_vector<int> permutation(N);
69 thrust::sequence(permutation.begin(), permutation.end());
70
71 // sort from least significant key to most significant keys
72 update_permutation(lower, permutation);
73 update_permutation(middle, permutation);
74 update_permutation(upper, permutation);
75
76 // Note: keys have not been modified
77 // Note: permutation now maps unsorted keys to sorted order
78
79 // permute the key arrays by the final permuation
80 apply_permutation(lower, permutation);
81 apply_permutation(middle, permutation);
82 apply_permutation(upper, permutation);
83
84 std::cout << "Sorted Keys" << std::endl;
85 for(size_t i = 0; i < N; i++)
86 {
87 std::cout << "(" << upper[i] << "," << middle[i] << "," << lower[i] << ")" << std::endl;
88 }
89
90 return 0;
91 }
92
93