1 files changed, 49 insertions, 0 deletions
diff --git a/intern/cycles/kernel/device/gpu/parallel_sorted_index.h b/intern/cycles/kernel/device/gpu/parallel_sorted_index.h
new file mode 100644
index 00000000000..99b35468517
--- /dev/null
+++ b/intern/cycles/kernel/device/gpu/parallel_sorted_index.h
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2021 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+CCL_NAMESPACE_BEGIN
+
+/* Given an array of states, build an array of indices for which the states
+ * are active and sorted by a given key. The prefix sum of the number of active
+ * states per key must have already been computed.
+ *
+ * TODO: there may be ways to optimize this to avoid this many atomic ops? */
+
+#include "util/util_atomic.h"
+
+#define GPU_PARALLEL_SORTED_INDEX_DEFAULT_BLOCK_SIZE 512
+#define GPU_PARALLEL_SORTED_INDEX_INACTIVE_KEY (~0)
+
+template<uint blocksize, typename GetKeyOp>
+__device__ void gpu_parallel_sorted_index_array(const uint num_states,
+                                                int *indices,
+                                                int *num_indices,
+                                                int *key_prefix_sum,
+                                                GetKeyOp get_key_op)
+{
+  const uint state_index = ccl_gpu_block_idx_x * blocksize + ccl_gpu_thread_idx_x;
+  const int key = (state_index < num_states) ? get_key_op(state_index) :
+                                               GPU_PARALLEL_SORTED_INDEX_INACTIVE_KEY;
+
+  if (key != GPU_PARALLEL_SORTED_INDEX_INACTIVE_KEY) {
+    const uint index = atomic_fetch_and_add_uint32(&key_prefix_sum[key], 1);
+    indices[index] = state_index;
+  }
+}
+
+CCL_NAMESPACE_END