Speed improvement with no AVX. 40% on Linux Intel Xeon and 60% on ARM Mac.

PiperOrigin-RevId: 488360660
Change-Id: I423269cd362fdcc2434393b691638ac6ed778ef2

test/engine/engine_util_sparse_test.cc

@@ -0,0 +1,44 @@
+// Copyright 2022 DeepMind Technologies Limited
+//
+// 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.
+
+// Tests for engine/engine_util_sparse.c
+
+#include "src/engine/engine_util_sparse.h"
+
+#include <gtest/gtest.h>
+#include "test/fixture.h"
+
+namespace mujoco {
+namespace {
+
+using EngineUtilSparseTest = MujocoTest;
+
+TEST_F(EngineUtilSparseTest, MjuDot) {
+  mjtNum a[] = {1, 2, 3, 4, 5, 6, 7};
+  mjtNum b[] = {7, 0, 6, 0, 0, 5, 0, 0, 0, 4, 0, 0, 0, 3, 0, 0, 2, 0, 1};
+  int i[] = {0, 2, 5, 9, 13, 16, 18};
+
+  // test various vector lengths as mju_dotSparse adds numbers in groups of four
+  EXPECT_EQ(mju_dotSparse(a, b, 0, i), 0);
+  EXPECT_EQ(mju_dotSparse(a, b, 1, i), 7);
+  EXPECT_EQ(mju_dotSparse(a, b, 2, i), 7 + 2*6);
+  EXPECT_EQ(mju_dotSparse(a, b, 3, i), 7 + 2*6 + 3*5);
+  EXPECT_EQ(mju_dotSparse(a, b, 4, i), 7 + 2*6 + 3*5 + 4*4);
+  EXPECT_EQ(mju_dotSparse(a, b, 5, i), 7 + 2*6 + 3*5 + 4*4 + 5*3);
+  EXPECT_EQ(mju_dotSparse(a, b, 6, i), 7 + 2*6 + 3*5 + 4*4 + 5*3 + 6*2);
+  EXPECT_EQ(mju_dotSparse(a, b, 7, i), 7 + 2*6 + 3*5 + 4*4 + 5*3 + 6*2 + 7);
+}
+
+}  // namespace
+}  // namespace mujoco