From 12e3c37d6a618866afbb03b029800329be3baad8 Mon Sep 17 00:00:00 2001
From: JafarAbdi <jafar.uruc@gmail.com>
Date: Mon, 25 Nov 2024 13:51:43 +0000
Subject: [PATCH 1/3] Fix ReinterpretAsInt causing undefind behavior +
 segfaulting on release mode

---
 mjpc/utilities.cc | 12 ++++++++----
 mjpc/utilities.h  |  4 ++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/mjpc/utilities.cc b/mjpc/utilities.cc
index 5c87cbf62..247c0748e 100644
--- a/mjpc/utilities.cc
+++ b/mjpc/utilities.cc
@@ -115,12 +115,16 @@ void Clamp(double* x, const double* bounds, int n) {
   }
 }
 
-int ReinterpretAsInt(double value) {
-  return *std::launder(reinterpret_cast<const int*>(&value));
+int64_t ReinterpretAsInt(double value) {
+  static_assert(sizeof(double) == sizeof(int64_t),
+                 "double and int64_t must have same size");
+  return std::bit_cast<int64_t>(value);
 }
 
 double ReinterpretAsDouble(int64_t value) {
-  return *std::launder(reinterpret_cast<const double*>(&value));
+  static_assert(sizeof(double) == sizeof(int64_t),
+                 "double and int64_t must have same size");
+  return std::bit_cast<double>(value);
 }
 
 absl::flat_hash_map<std::string, std::vector<std::string>>
@@ -225,7 +229,7 @@ int ParameterIndex(const mjModel* model, std::string_view name) {
 double DefaultResidualSelection(const mjModel* m, int numeric_index) {
   // list selections are stored as ints, but numeric values are doubles.
   int64_t value = m->numeric_data[m->numeric_adr[numeric_index]];
-  return *std::launder(reinterpret_cast<const double*>(&value));
+  return ReinterpretAsDouble(value);
 }
 
 int CostTermByName(const mjModel* m, const std::string& name) {
diff --git a/mjpc/utilities.h b/mjpc/utilities.h
index f3eb5c8a0..f5c88cd54 100644
--- a/mjpc/utilities.h
+++ b/mjpc/utilities.h
@@ -66,8 +66,8 @@ T GetNumberOrDefault(T default_value, const mjModel* m, std::string_view name) {
   return GetNumber<T>(m, name).value_or(default_value);
 }
 
-// reinterpret double as int
-int ReinterpretAsInt(double value);
+// reinterpret double as int64_t
+int64_t ReinterpretAsInt(double value);
 
 // reinterpret int64_t as double
 double ReinterpretAsDouble(int64_t value);

From 5385f368107b7a7ddba6f283d3f85cd54eeb2fa3 Mon Sep 17 00:00:00 2001
From: JafarAbdi <jafar.uruc@gmail.com>
Date: Mon, 25 Nov 2024 14:45:13 +0000
Subject: [PATCH 2/3] Include bit header file

---
 mjpc/utilities.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mjpc/utilities.cc b/mjpc/utilities.cc
index 247c0748e..0d9cbe1b0 100644
--- a/mjpc/utilities.cc
+++ b/mjpc/utilities.cc
@@ -15,6 +15,7 @@
 #include "mjpc/utilities.h"
 
 #include <algorithm>
+#include <bit>
 #include <cerrno>
 #include <cmath>
 #include <cstdint>

From d8a7ff776db351cef453520fdf63355634b8ffb2 Mon Sep 17 00:00:00 2001
From: JafarAbdi <jafar.uruc@gmail.com>
Date: Mon, 25 Nov 2024 19:45:25 +0000
Subject: [PATCH 3/3] Make all compilers happy

---
 mjpc/utilities.cc | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/mjpc/utilities.cc b/mjpc/utilities.cc
index 0d9cbe1b0..6f67c27e5 100644
--- a/mjpc/utilities.cc
+++ b/mjpc/utilities.cc
@@ -118,14 +118,26 @@ void Clamp(double* x, const double* bounds, int n) {
 
 int64_t ReinterpretAsInt(double value) {
   static_assert(sizeof(double) == sizeof(int64_t),
-                 "double and int64_t must have same size");
+                "double and int64_t must have same size");
+#if defined(__cpp_lib_bit_cast)
   return std::bit_cast<int64_t>(value);
+#else
+  int64_t dst;
+  std::memcpy(&dst, &value, sizeof(int64_t));
+  return dst;
+#endif
 }
 
 double ReinterpretAsDouble(int64_t value) {
   static_assert(sizeof(double) == sizeof(int64_t),
-                 "double and int64_t must have same size");
+                "double and int64_t must have same size");
+#if defined(__cpp_lib_bit_cast)
   return std::bit_cast<double>(value);
+#else
+  double dst;
+  std::memcpy(&dst, &value, sizeof(double));
+  return dst;
+#endif
 }
 
 absl::flat_hash_map<std::string, std::vector<std::string>>