[Misc] Polish metapath_randomwalk.h (#5471)

Co-authored-by: Ubuntu <ubuntu@ip-172-31-28-63.ap-northeast-1.compute.internal>

src/graph/sampling/randomwalks/metapath_randomwalk.h

@@ -2,7 +2,7 @@
  *  Copyright (c) 2018 by Contributors
  * @file graph/sampler/generic_randomwalk_cpu.h
  * @brief DGL sampler - templated implementation definition of random walks on
- * CPU
+ *     CPU.
  */
 
 #ifndef DGL_GRAPH_SAMPLING_RANDOMWALKS_METAPATH_RANDOMWALK_H_
@@ -30,21 +30,17 @@ namespace impl {
 
 namespace {
 
-// bool WhetherToTerminate(
-//     IdxType *node_ids_generated_so_far,
-//     dgl_id_t last_node_id_generated,
-//     int64_t number_of_nodes_generated_so_far)
 template <typename IdxType>
 using TerminatePredicate = std::function<bool(IdxType *, dgl_id_t, int64_t)>;
 
 /**
  * @brief Select one successor of metapath-based random walk, given the path
- * generated so far.
+ *     generated so far.
  *
  * @param data The path generated so far, of type \c IdxType.
  * @param curr The last node ID generated.
  * @param len The number of nodes generated so far.  Note that the seed node is
- * always included as \c data[0], and the successors start from \c data[1].
+ *     always included as \c data[0], and the successors start from \c data[1].
  *
  * @param edges_by_type Vector of results from \c GetAdj() by edge type.
  * @param metapath_data Edge types of given metapath.
@@ -52,7 +48,7 @@ using TerminatePredicate = std::function<bool(IdxType *, dgl_id_t, int64_t)>;
  * @param terminate Predicate for terminating the current random walk path.
  *
  * @return A tuple of ID of next successor (-1 if not exist), the last traversed
- * edge ID, as well as whether to terminate.
+ *     edge ID, as well as whether to terminate.
  */
 template <DGLDeviceType XPU, typename IdxType>
 std::tuple<dgl_id_t, dgl_id_t, bool> MetapathRandomWalkStep(
@@ -78,9 +74,9 @@ std::tuple<dgl_id_t, dgl_id_t, bool> MetapathRandomWalkStep(
   const int64_t size = offsets[curr + 1] - offsets[curr];
   if (size == 0) return std::make_tuple(-1, -1, true);
 
-  // Use a reference to the original array instead of copying
-  // This avoids updating the ref counts atomically from different threads
-  // and avoids cache ping-ponging in the tight loop
+  // Use a reference to the original array instead of copying. This avoids
+  // updating the ref counts atomically from different threads and avoids cache
+  // ping-ponging in the tight loop.
   const FloatArray &prob_etype = prob[etype];
   IdxType idx = 0;
   if (IsNullArray(prob_etype)) {
@@ -105,23 +101,22 @@ std::tuple<dgl_id_t, dgl_id_t, bool> MetapathRandomWalkStep(
 
 /**
  * @brief Select one successor of metapath-based random walk, given the path
- * generated so far specifically for the uniform probability distribution.
+ *     generated so far specifically for the uniform probability distribution.
  *
  * @param data The path generated so far, of type \c IdxType.
  * @param curr The last node ID generated.
  * @param len The number of nodes generated so far.  Note that the seed node is
- * always included as \c data[0], and the successors start from \c data[1].
+ *     always included as \c data[0], and the successors start from \c data[1].
  *
  * @param edges_by_type Vector of results from \c GetAdj() by edge type.
  * @param metapath_data Edge types of given metapath.
  * @param prob Transition probability per edge type, for this special case this
- * will be a NullArray
- * @param terminate Predicate for terminating the current
- * random walk path.
+ *     will be a NullArray.
+ * @param terminate Predicate for terminating the current random walk path.
  *
  * @return A pair of ID of next successor (-1 if not exist), as well as whether
- * to terminate. \note This function is called only if all the probability
- * arrays are null.
+ *     to terminate. \note This function is called only if all the probability
+ *     arrays are null.
  */
 template <DGLDeviceType XPU, typename IdxType>
 std::tuple<dgl_id_t, dgl_id_t, bool> MetapathRandomWalkStepUniform(
@@ -159,14 +154,14 @@ std::tuple<dgl_id_t, dgl_id_t, bool> MetapathRandomWalkStepUniform(
  * @brief Metapath-based random walk.
  * @param hg The heterograph.
  * @param seeds A 1D array of seed nodes, with the type the source type of the
- * first edge type in the metapath.
+ *     first edge type in the metapath.
  * @param metapath A 1D array of edge types representing the metapath.
  * @param prob A vector of 1D float arrays, indicating the transition
- * probability of each edge by edge type.  An empty float array assumes uniform
- * transition.
+ *     probability of each edge by edge type.  An empty float array assumes
+ *     uniform transition.
  * @param terminate Predicate for terminating a random walk path.
  * @return A 2D array of shape (len(seeds), len(metapath) + 1) with node IDs,
- * and A 2D array of shape (len(seeds), len(metapath)) with edge IDs.
+ *     and A 2D array of shape (len(seeds), len(metapath)) with edge IDs.
  */
 template <DGLDeviceType XPU, typename IdxType>
 std::pair<IdArray, IdArray> MetapathBasedRandomWalk(