Dynamically allocate contact and efc_ arrays on a new memory arena.

- Add private function `mj_arenaAlloc`. This is used internally to allocate memory from the arena.

- Add private function `mj_nefc` to count constraints. This function returns a tight upper bound on `d->nefc`. The number of counted constraints can be slightly bigger than exact `d->nefc` in the case of constraints with empty Jacobian, as when placing a frictional tendon between two world sites.

- Add new `memory` attribute to the `size` XML element for specification of arena memory size. This attribute is mutually exclusive with `nstack` and `njmax` specifications, which are now deprecated (but left around for the time being for legacy compatibility).

- Move `d->stack` to the end of the new arena space. The stack now grows in reverse from the end.

PiperOrigin-RevId: 479341539
Change-Id: Ie019c202e0908577ffc6f833a37920858116f667

src/engine/engine_macro.h

@@ -15,6 +15,8 @@
 #ifndef MUJOCO_SRC_ENGINE_ENGINE_MACRO_H_
 #define MUJOCO_SRC_ENGINE_ENGINE_MACRO_H_
 
+#include <stdint.h>
+
 #include "engine/engine_callback.h"  // IWYU pragma: export
 
 //-------------------------------- utility macros --------------------------------------------------
@@ -40,4 +42,35 @@
 #define TM_START1 mjtNum _tm1 = (mjcb_time ? mjcb_time() : 0);
 #define TM_END1(i) {d->timer[i].duration += ((mjcb_time ? mjcb_time() : 0) - _tm1); d->timer[i].number++;}
 
+//-------------------------- sanitizer macros ------------------------------------------------------
+
+#ifdef ADDRESS_SANITIZER
+  #include <sanitizer/asan_interface.h>
+#elif defined(_MSC_VER)
+  #define ASAN_POISON_MEMORY_REGION(addr, size)
+  #define ASAN_UNPOISON_MEMORY_REGION(addr, size)
+#else
+  #define ASAN_POISON_MEMORY_REGION(addr, size) ((void)(addr), (void)(size))
+  #define ASAN_UNPOISON_MEMORY_REGION(addr, size) ((void)(addr), (void)(size))
+#endif
+
+#ifdef MEMORY_SANITIZER
+  #include <sanitizer/msan_interface.h>
+#endif
+
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+//-------------------------- pointer arithmetic ----------------------------------------------------
+
+#define PTRDIFF(x, y) ((char*)(x) - (char*)(y))
+
+// number of bytes to be skipped to achieve 64-byte alignment
+static inline unsigned int SKIP(intptr_t offset) {
+  const unsigned int align = 64;
+  // compute skipped bytes
+  return (align - (offset % align)) % align;
+}
+
 #endif  // MUJOCO_SRC_ENGINE_ENGINE_MACRO_H_