Faster ReverseSequence CPU implementation (#981)

* clean up, rename

*  remove commented code; add comments

src/ngraph/runtime/cpu/cpu_emitter.cpp

@@ -2828,15 +2828,76 @@ namespace ngraph
             void CPU_Emitter::EMITTER_DECL(ngraph::op::ReverseSequence)
             {
                 auto rs = static_cast<const ngraph::op::ReverseSequence*>(node);
+
+                string iv_prefix{"i"};
+                size_t ibi = rs->get_batch_axis();
+                string bi = iv_prefix + std::to_string(ibi);
+                string si = iv_prefix + std::to_string(rs->get_sequence_axis());
                 auto arg_shape = args[0].get_shape();
 
-                writer << "reference::reverse_sequence<" << out[0].get_type() << ","
-                       << args[1].get_type() << ">(" << args[0].get_name() << ",\n";
-                writer << "                " << out[0].get_name() << ",\n";
-                writer << "                {" << join(arg_shape) << "},\n";
-                writer << "                 " << rs->get_batch_axis() << ",\n";
-                writer << "                 " << rs->get_sequence_axis() << ",\n";
-                writer << "                 " << args[1].get_name() << ");\n";
+                //iterate over seq_lengths make sure indices aren't out of bounds and normalize
+                writer << "std::vector<size_t> norm_seq_lengths (" << arg_shape.at(ibi) << ");\n";
+                writer << emit_for_lt(iv_prefix, ibi, arg_shape.at(ibi));
+                writer.block_begin();
+                writer << "auto seq_len = static_cast<size_t>(" << args[1].get_name() << "[" << bi
+                       << "]);\n";
+                writer << "if (seq_len > " << arg_shape.at(rs->get_sequence_axis()) << ")\n";
+                writer.block_begin();
+                writer << "throw \"One of the elements of sequence lengths is greater than "
+                          "sequence axis\";\n";
+                writer.block_end();
+
+                writer << "if (seq_len == 0)\n";
+                writer.block_begin();
+                writer << "norm_seq_lengths[" << bi << "] = 1;\n";
+                writer.block_end();
+                writer << " else \n";
+                writer.block_begin();
+                writer << "norm_seq_lengths[" << bi << "] = seq_len;\n";
+                writer.block_end();
+
+                writer.block_end();
+
+                std::vector<std::string> sdims;
+                for (auto d : arg_shape)
+                {
+                    sdims.push_back(std::to_string(d));
+                }
+
+                //convert input and output into multidimensional arrays
+                auto isdims = emit_indices(sdims);
+                writer << args[0].get_type() << "(&src)" << isdims << " = *reinterpret_cast<"
+                       << args[0].get_type() << " (*)" << isdims << ">(" << args[0].get_name()
+                       << ");\n";
+
+                writer << args[0].get_type() << "(&dst)" << isdims << " = *reinterpret_cast<"
+                       << args[0].get_type() << " (*)" << isdims << ">(" << out[0].get_name()
+                       << ");\n";
+
+                //reverse sequence
+                std::vector<std::string> source_indices;
+                for (size_t i = 0; i < arg_shape.size(); i++)
+                {
+                    writer << emit_for_lt(iv_prefix, i, arg_shape.at(i));
+                    writer.block_begin();
+                    source_indices.push_back(iv_prefix + std::to_string(i));
+                }
+
+                writer << "auto seq_len = norm_seq_lengths[" << bi << "];\n";
+                writer << "size_t sequence_index = " << si << " < seq_len "
+                       << "? seq_len - " << si << " - 1"
+                       << ": " << si << ";\n";
+
+                std::vector<std::string> output_indices(source_indices);
+                output_indices.at(rs->get_sequence_axis()) = "sequence_index";
+
+                writer << "dst" << emit_indices(output_indices) << " = "
+                       << "src" << emit_indices(source_indices) << ";\n";
+
+                for (size_t i = 0; i < arg_shape.size(); i++)
+                {
+                    writer.block_end();
+                }
             }
 
             template <>
@@ -3832,7 +3893,26 @@ static string format_name(const string& name)
     return rc;
 }
 
-string runtime::cpu::CPU_Emitter::emit_vector(const runtime::cpu::TensorViewWrapper& tvi,
+std::string runtime::cpu::CPU_Emitter::emit_indices(const std::vector<std::string> indices)
+{
+    stringstream ss;
+    for (auto i : indices)
+    {
+        ss << "[" << i << "]";
+    }
+    return ss.str();
+}
+
+std::string
+    runtime::cpu::CPU_Emitter::emit_for_lt(const std::string& prefix, size_t index, size_t to)
+{
+    stringstream ss;
+    auto iv = prefix + std::to_string(index);
+    ss << "for (size_t " << iv << " = 0 ; " << iv << " < " << to << "; " << iv << "++)\n";
+    return ss.str();
+}
+
+std::string runtime::cpu::CPU_Emitter::emit_vector(const runtime::cpu::TensorViewWrapper& tvi,
                                                    const string& name)
 {
     stringstream ss;

src/ngraph/runtime/cpu/cpu_emitter.hpp

@@ -72,6 +72,9 @@ namespace ngraph
                                                 const std::string& name = "");
                 static std::string emit_matrix(const TensorViewWrapper&,
                                                const std::string& name = "");
+
+                static std::string emit_for_lt(const std::string& prefix, size_t index, size_t to);
+                static std::string emit_indices(const std::vector<std::string> indices);
             };
         }
     }