Move CompareModel to a separate library.

PiperOrigin-RevId: 927174846
Change-Id: Ia8b8b2c8593133d8910399be755e614282bf3252

test/CMakeLists.txt

@@ -104,6 +104,12 @@ target_link_libraries(
 )
 target_include_directories(fixture PRIVATE ${mujoco_SOURCE_DIR}/include gmock)
 
+add_library(compare_model STATIC compare_model.h compare_model.cc)
+target_include_directories(compare_model PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/..)
+target_compile_definitions(compare_model PUBLIC MJSTATIC)
+target_link_libraries(compare_model PUBLIC mujoco::mujoco)
+target_include_directories(compare_model PRIVATE ${mujoco_SOURCE_DIR}/include)
+
 mujoco_test(fixture_test)
 
 mujoco_test(header_test)

test/compare_model.cc

@@ -0,0 +1,138 @@
+// Copyright 2026 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 "test/compare_model.h"
+
+#include <cmath>
+#include <cstring>
+#include <limits>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+#include <mujoco/mjmodel.h>
+#include <mujoco/mjxmacro.h>
+#include <mujoco/mujoco.h>
+
+namespace mujoco {
+namespace {
+
+template <typename T>
+auto Compare(T val1, T val2);
+
+auto Compare(char val1, char val2) {
+  return val1 != val2;
+}
+
+auto Compare(unsigned char val1, unsigned char val2) {
+  return val1 != val2;
+}
+
+auto Compare(bool val1, bool val2) {
+  return val1 != val2;
+}
+
+auto Compare(mjtSize val1, mjtSize val2) {
+  return val1 > val2 ? val1 - val2 : val2 - val1;
+}
+
+// The maximum spacing between a normalised floating point number x and an
+// adjacent normalised number is 2 epsilon |x|; a factor 10 is added accounting
+// for losses during non-idempotent operations such as vector normalizations.
+template <typename T>
+auto Compare(T val1, T val2) {
+  using ReturnType =
+      std::conditional_t<std::is_same_v<T, float>, float, double>;
+  ReturnType error;
+  if (std::abs(val1) <= 1 || std::abs(val2) <= 1) {
+      // Absolute precision for small numbers
+      error = std::abs(val1-val2);
+  } else {
+    // Relative precision for larger numbers
+    ReturnType magnitude = std::abs(val1) + std::abs(val2);
+    error = std::abs(val1/magnitude - val2/magnitude) / magnitude;
+  }
+  ReturnType safety_factor = 200;
+  return error < safety_factor * std::numeric_limits<ReturnType>::epsilon()
+             ? 0
+             : error;
+}
+
+}  // namespace
+
+mjtNum CompareModel(const mjModel* m1, const mjModel* m2,
+                    std::string& field) {
+  mjtNum dif, maxdif = 0.0;
+
+  // define symbols corresponding to number of columns
+  // (needed in MJMODEL_POINTERS)
+  MJMODEL_POINTERS_PREAMBLE(m1);
+
+// compare ints, exclude nbuffer because it hides the actual difference
+#define X(name)                                           \
+  if constexpr (std::string_view(#name) != "nbuffer") {   \
+    if (m1->name != m2->name) {                           \
+      maxdif = std::abs((long)m1->name - (long)m2->name); \
+      field = #name;                                      \
+    }                                                     \
+  }
+  MJMODEL_SIZES
+#undef X
+  if (maxdif > 0) return maxdif;
+
+  // compare arrays, apart from bvh-related ones (which includes flex_vert0), as
+  // those are sensitive to numerical differences when meshes are perfectly
+  // symmetric.  Also skip flex fields derived from node local positions and
+  // cell geometry that are not fully serialized to XML.
+#define X(type, name, nr, nc)                                         \
+  if (strncmp(#name, "bvh_", 4) &&                                    \
+      strncmp(#name, "flex_vert", 9) &&                               \
+      strncmp(#name, "mesh_poly", 9) &&                               \
+      strcmp(#name, "flex_centered") &&                               \
+      strcmp(#name, "flex_size") &&                                   \
+      strcmp(#name, "flexedge_length0") &&                            \
+      strcmp(#name, "flexedge_invweight0") &&                         \
+      strncmp(#name, "flex_node", 9)) {                               \
+    for (int r = 0; r < m1->nr; r++) {                                \
+      for (int c = 0; c < nc; c++) {                                  \
+        dif = Compare(m1->name[r * nc + c], m2->name[r * nc + c]);    \
+        if (dif > maxdif) {                                           \
+          maxdif = dif;                                               \
+          field = #name;                                              \
+          field += " row: " + std::to_string(r);                      \
+          field += " col: " + std::to_string(c);                      \
+        }                                                             \
+      }                                                               \
+    }                                                                 \
+  }  // NOLINT
+  MJMODEL_POINTERS
+#undef X
+
+  // compare fields in mjOption
+  #define X(type, name, n)                                         \
+    dif = Compare(m1->opt.name, m2->opt.name);                     \
+    if (dif > maxdif) {maxdif = dif; field = #name;}
+  #define XVEC(type, name, n)                                    \
+    for (int c=0; c < n; c++) {                                  \
+      dif = Compare(m1->opt.name[c], m2->opt.name[c]);           \
+      if (dif > maxdif) {maxdif = dif; field = #name;} }
+    MJOPTION_FIELDS
+  #undef XVEC
+  #undef X
+
+  // Return largest difference and field name
+  return maxdif;
+}
+
+}  // namespace mujoco

test/compare_model.h

@@ -0,0 +1,30 @@
+// Copyright 2026 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.
+
+#ifndef MUJOCO_TEST_COMPARE_MODEL_H_
+#define MUJOCO_TEST_COMPARE_MODEL_H_
+
+#include <string>
+
+#include <mujoco/mujoco.h>
+
+namespace mujoco {
+
+// Compares all fields of two mjModels.
+// Returns the name of the different field and the max difference.
+mjtNum CompareModel(const mjModel* m1, const mjModel* m2, std::string& field);
+
+}  // namespace mujoco
+
+#endif  // MUJOCO_TEST_COMPARE_MODEL_H_

test/fixture.cc

@@ -192,110 +192,6 @@ std::vector<mjtNum> GetCtrlNoise(const mjModel* m, int nsteps,
   return ctrl;
 }
 
-template <typename T>
-auto Compare(T val1, T val2);
-
-auto Compare(char val1, char val2) {
-  return val1 != val2;
-}
-
-auto Compare(unsigned char val1, unsigned char val2) {
-  return val1 != val2;
-}
-
-auto Compare(bool val1, bool val2) {
-  return val1 != val2;
-}
-
-auto Compare(mjtSize val1, mjtSize val2) {
-  return val1 > val2 ? val1 - val2 : val2 - val1;
-}
-
-// The maximum spacing between a normalised floating point number x and an
-// adjacent normalised number is 2 epsilon |x|; a factor 10 is added accounting
-// for losses during non-idempotent operations such as vector normalizations.
-template <typename T>
-auto Compare(T val1, T val2) {
-  using ReturnType =
-      std::conditional_t<std::is_same_v<T, float>, float, double>;
-  ReturnType error;
-  if (std::abs(val1) <= 1 || std::abs(val2) <= 1) {
-      // Absolute precision for small numbers
-      error = std::abs(val1-val2);
-  } else {
-    // Relative precision for larger numbers
-    ReturnType magnitude = std::abs(val1) + std::abs(val2);
-    error = std::abs(val1/magnitude - val2/magnitude) / magnitude;
-  }
-  ReturnType safety_factor = 200;
-  return error < safety_factor * std::numeric_limits<ReturnType>::epsilon()
-             ? 0
-             : error;
-}
-
-mjtNum CompareModel(const mjModel* m1, const mjModel* m2,
-                    std::string& field) {
-  mjtNum dif, maxdif = 0.0;
-
-  // define symbols corresponding to number of columns
-  // (needed in MJMODEL_POINTERS)
-  MJMODEL_POINTERS_PREAMBLE(m1);
-
-// compare ints, exclude nbuffer because it hides the actual difference
-#define X(name)                                           \
-  if constexpr (std::string_view(#name) != "nbuffer") {   \
-    if (m1->name != m2->name) {                           \
-      maxdif = std::abs((long)m1->name - (long)m2->name); \
-      field = #name;                                      \
-    }                                                     \
-  }
-  MJMODEL_SIZES
-#undef X
-  if (maxdif > 0) return maxdif;
-
-  // compare arrays, apart from bvh-related ones (which includes flex_vert0), as
-  // those are sensitive to numerical differences when meshes are perfectly
-  // symmetric.  Also skip flex fields derived from node local positions and
-  // cell geometry that are not fully serialized to XML.
-#define X(type, name, nr, nc)                                         \
-  if (strncmp(#name, "bvh_", 4) &&                                    \
-      strncmp(#name, "flex_vert", 9) &&                               \
-      strncmp(#name, "mesh_poly", 9) &&                               \
-      strcmp(#name, "flex_centered") &&                               \
-      strcmp(#name, "flex_size") &&                                   \
-      strcmp(#name, "flexedge_length0") &&                            \
-      strcmp(#name, "flexedge_invweight0") &&                         \
-      strncmp(#name, "flex_node", 9)) {                               \
-    for (int r = 0; r < m1->nr; r++) {                                \
-      for (int c = 0; c < nc; c++) {                                  \
-        dif = Compare(m1->name[r * nc + c], m2->name[r * nc + c]);    \
-        if (dif > maxdif) {                                           \
-          maxdif = dif;                                               \
-          field = #name;                                              \
-          field += " row: " + std::to_string(r);                      \
-          field += " col: " + std::to_string(c);                      \
-        }                                                             \
-      }                                                               \
-    }                                                                 \
-  }  // NOLINT
-  MJMODEL_POINTERS
-#undef X
-
-  // compare fields in mjOption
-  #define X(type, name, n)                                         \
-    dif = Compare(m1->opt.name, m2->opt.name);                     \
-    if (dif > maxdif) {maxdif = dif; field = #name;}
-  #define XVEC(type, name, n)                                    \
-    for (int c=0; c < n; c++) {                                  \
-      dif = Compare(m1->opt.name[c], m2->opt.name[c]);           \
-      if (dif > maxdif) {maxdif = dif; field = #name;} }
-    MJOPTION_FIELDS
-  #undef XVEC
-  #undef X
-
-  // Return largest difference and field name
-  return maxdif;
-}
 
 MockFilesystem::MockFilesystem(std::string unit_test_name) {
   prefix_ = absl::StrCat("MjMock.", unit_test_name);

test/fixture.h

@@ -182,9 +182,6 @@ std::string SaveAndReadXml(const mjSpec* spec);
 std::vector<mjtNum> GetCtrlNoise(const mjModel* m, int nsteps,
                                  mjtNum ctrlnoise = 0.01);
 
-// Compares all fields of two mjModels.
-// Returns the name of the different field and the max difference.
-mjtNum CompareModel(const mjModel* m1, const mjModel* m2, std::string& field);
 
 // Returns a vector containing the elements of the array.
 template <typename T>

test/user/CMakeLists.txt

@@ -14,13 +14,14 @@
 
 mujoco_test(
   user_model_test
-  ADDITIONAL_LINK_LIBRARIES absl::str_format
+  ADDITIONAL_LINK_LIBRARIES absl::str_format compare_model
 )
 
 mujoco_test(user_objects_test)
 
 mujoco_test(
   user_api_test
+  ADDITIONAL_LINK_LIBRARIES compare_model
   PROPERTIES
   ENVIRONMENT
   "MUJOCO_PLUGIN_DIR=$<TARGET_FILE_DIR:elasticity>"
@@ -28,6 +29,7 @@ mujoco_test(
 
 mujoco_test(
   user_recompile_test
+  ADDITIONAL_LINK_LIBRARIES compare_model
   PROPERTIES
   ENVIRONMENT
   "MUJOCO_PLUGIN_DIR=$<TARGET_FILE_DIR:elasticity>"

test/user/user_api_test.cc

@@ -31,6 +31,7 @@
 #include <mujoco/mjspec.h>
 #include <mujoco/mjplugin.h>
 #include "src/xml/xml_api.h"
+#include "test/compare_model.h"
 #include "test/fixture.h"
 
 namespace mujoco {

test/user/user_model_test.cc

@@ -26,6 +26,7 @@
 #include <absl/strings/str_format.h>
 #include <mujoco/mjmodel.h>
 #include <mujoco/mujoco.h>
+#include "test/compare_model.h"
 #include "test/fixture.h"
 
 namespace mujoco {

test/user/user_recompile_test.cc

@@ -29,6 +29,7 @@
 #include <mujoco/mjspec.h>
 #include "src/xml/xml_api.h"
 #include "src/xml/xml_numeric_format.h"
+#include "test/compare_model.h"
 #include "test/fixture.h"
 
 namespace mujoco {

test/xml/CMakeLists.txt

@@ -16,6 +16,7 @@ mujoco_test(xml_api_test)
 
 mujoco_test(
   xml_native_reader_test
+  ADDITIONAL_LINK_LIBRARIES compare_model
 )
 
 mujoco_test(xml_utils_test)
@@ -33,6 +34,7 @@ mujoco_test(
   xml_write_read_test
   ADDITIONAL_LINK_LIBRARIES
   absl::flat_hash_set
+  compare_model
   PROPERTIES
   ENVIRONMENT
   "MUJOCO_PLUGIN_DIR=$<TARGET_FILE_DIR:elasticity>"

test/xml/mjz/CMakeLists.txt

@@ -20,4 +20,5 @@ mujoco_test(
 
 mujoco_test(
   mjz_encoder_test
+  ADDITIONAL_LINK_LIBRARIES compare_model
 )

test/xml/mjz/mjz_encoder_test.cc

@@ -31,6 +31,7 @@
 #include <mujoco/mjspec.h>
 #include <mujoco/mujoco.h>
 #include "src/xml/xml_numeric_format.h"
+#include "test/compare_model.h"
 #include "test/fixture.h"
 
 namespace mujoco {

test/xml/xml_native_reader_test.cc

@@ -30,6 +30,7 @@
 #include "src/cc/array_safety.h"
 #include "src/engine/engine_util_errmem.h"
 #include "src/xml/xml_api.h"
+#include "test/compare_model.h"
 #include "test/fixture.h"
 
 namespace mujoco {

test/xml/xml_write_read_test.cc

@@ -28,6 +28,7 @@
 #include <mujoco/mjmodel.h>
 #include <mujoco/mujoco.h>
 #include "src/xml/xml_numeric_format.h"
+#include "test/compare_model.h"
 #include "test/fixture.h"
 
 namespace mujoco {