mjQUICKSORT uses std::sort with C++.

fixes #1638

PiperOrigin-RevId: 660887790
Change-Id: Ia3b493feda98b246d963aa749bc81b96c42fddaa

test/engine/engine_sort_test.cc

@@ -0,0 +1,74 @@
+// Copyright 2024 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.
+
+#include "src/engine/engine_sort.h"
+
+#include <cstddef>
+#include <vector>
+
+#include <gtest/gtest.h>
+#include "src/engine/engine_sort.h"
+#include "test/fixture.h"
+
+namespace mujoco {
+namespace {
+
+using EngineSortTest = MujocoTest;
+
+struct IntStruct {
+  int value;
+};
+
+quicksortfunc(int_compare, context, x, y) {
+  int a = *(int*)x;
+  int b = *(int*)y;
+  if (a < b) {
+    return -1;
+  } else if (a == b) {
+    return 0;
+  } else {
+    return 1;
+  }
+}
+
+quicksortfunc(intstruct_compare, context, x, y) {
+  IntStruct* a = (IntStruct*)x;
+  IntStruct* b = (IntStruct*)y;
+  if (a->value < b->value) {
+    return -1;
+  } else if (a->value == b->value) {
+    return 0;
+  } else {
+    return 1;
+  }
+}
+
+TEST_F(EngineSortTest, Sort) {
+  // test int
+  std::vector<int> x = {1, 3, 2};
+  mjQUICKSORT(x.data(), x.size(), sizeof(int), int_compare, x.data());
+  EXPECT_EQ(x[0], 1);
+  EXPECT_EQ(x[1], 2);
+  EXPECT_EQ(x[2], 3);
+
+  // test custom struct with mjQUICKSORT
+  std::vector<IntStruct> y = {{.value = 1}, {.value = 3}, {.value = 2}};
+  mjQUICKSORT(y.data(), y.size(), sizeof(IntStruct), intstruct_compare, NULL);
+  EXPECT_EQ(y[0].value, 1);
+  EXPECT_EQ(y[1].value, 2);
+  EXPECT_EQ(y[2].value, 3);
+}
+
+}  // namespace
+}  // namespace mujoco