Merge pull request boostorg#803 from rosenrodt/fix-dupe-with-custom-compare-bitonic-block-sort

Fix duplicates using custom compare with bitonic block sort

Author: jszuppe

include/boost/compute/algorithm/detail/merge_sort_on_gpu.hpp

@@ -170,8 +170,12 @@ inline size_t bitonic_block_sort(KeyIterator keys_first,
             k.decl<bool>("compare") << " = " <<
                 compare(k.var<key_type>("sibling_key"),
                         k.var<key_type>("my_key")) << ";\n" <<
+            k.decl<bool>("equal") << " = !(compare || " <<
+                compare(k.var<key_type>("my_key"),
+                        k.var<key_type>("sibling_key")) << ");\n" <<
             k.decl<bool>("swap") <<
                 " = compare ^ (sibling_idx < lid) ^ direction;\n" <<
+            "swap = equal ? false : swap;\n" <<
             "my_key = swap ? sibling_key : my_key;\n";
     if(sort_by_key)
     {
@@ -220,8 +224,12 @@ inline size_t bitonic_block_sort(KeyIterator keys_first,
             k.decl<bool>("compare") << " = " <<
                 compare(k.var<key_type>("sibling_key"),
                         k.var<key_type>("my_key")) << ";\n" <<
+            k.decl<bool>("equal") << " = !(compare || " <<
+                compare(k.var<key_type>("my_key"),
+                        k.var<key_type>("sibling_key")) << ");\n" <<
             k.decl<bool>("swap") <<
                 " = compare ^ (sibling_idx < lid);\n" <<
+            "swap = equal ? false : swap;\n" <<
             "my_key = swap ? sibling_key : my_key;\n";
     if(sort_by_key)
     {

test/test_sort.cpp

@@ -340,6 +340,7 @@ BOOST_AUTO_TEST_CASE(sort_int2)
     host[size/4] = int2_(20.f, 0.f);
     host[(size*3)/4] = int2_(9.f, 0.f);
     host[size-3] = int2_(-10.0f, 0.f);
+    host[size/2+1] = int2_(-10.0f, -1.f);
 
     boost::compute::vector<int2_> vector(size, context);
     boost::compute::copy(host.begin(), host.end(), vector.begin(), queue);
@@ -356,9 +357,11 @@ BOOST_AUTO_TEST_CASE(sort_int2)
     );
     boost::compute::copy(vector.begin(), vector.end(), host.begin(), queue);
     BOOST_CHECK_CLOSE(host[0][0], -10.f, 0.1);
+    BOOST_CHECK_CLOSE(host[1][0], -10.f, 0.1);
     BOOST_CHECK_CLOSE(host[(size - 3)][0], 9.f, 0.1);
     BOOST_CHECK_CLOSE(host[(size - 2)][0], 20.f, 0.1);
     BOOST_CHECK_CLOSE(host[(size - 1)][0], 100.f, 0.1);
+    BOOST_CHECK_NE(host[0], host[1]);
 }
 
 BOOST_AUTO_TEST_SUITE_END()