Remove usage of size_t types in mjModel, use mjtSize (uint64_t) instead to improve portabilty of MJB files to WASM.

PiperOrigin-RevId: 789321991
Change-Id: Ic25fab876c347fc75f5ca24cad09e8fd972f035f

include/mujoco/mjdata.h

@@ -162,8 +162,8 @@ typedef struct mjSolverStat_ mjSolverStat;
 
 struct mjData_ {
   // constant sizes
-  size_t  narena;            // size of the arena in bytes (inclusive of the stack)
-  size_t  nbuffer;           // size of main buffer in bytes
+  mjtSize narena;            // size of the arena in bytes (inclusive of the stack)
+  mjtSize nbuffer;           // size of main buffer in bytes
   int     nplugin;           // number of plugin instances
 
   // stack pointer
@@ -174,9 +174,9 @@ struct mjData_ {
   size_t  parena;            // first available byte in arena
 
   // memory utilization statistics
-  size_t  maxuse_stack;                       // maximum stack allocation in bytes
-  size_t  maxuse_threadstack[mjMAXTHREAD];    // maximum stack allocation per thread in bytes
-  size_t  maxuse_arena;                       // maximum arena allocation in bytes
+  mjtSize maxuse_stack;                       // maximum stack allocation in bytes
+  mjtSize maxuse_threadstack[mjMAXTHREAD];    // maximum stack allocation per thread in bytes
+  mjtSize maxuse_arena;                       // maximum arena allocation in bytes
   int     maxuse_con;                         // maximum number of contacts
   int     maxuse_efc;                         // maximum number of scalar constraints
 

include/mujoco/mjmodel.h

@@ -731,8 +731,8 @@ struct mjModel_ {
   int nsensordata;                // number of mjtNums in sensor data vector
   int npluginstate;               // number of mjtNums in plugin state vector
 
-  size_t narena;                  // number of bytes in the mjData arena (inclusive of stack)
-  size_t nbuffer;                 // number of bytes in buffer
+  mjtSize narena;                 // number of bytes in the mjData arena (inclusive of stack)
+  mjtSize nbuffer;                // number of bytes in buffer
 
   // ------------------------------- options and statistics
 

include/mujoco/mjspec.h

@@ -170,7 +170,7 @@ typedef struct mjSpec_ {           // model specification
   mjStatistic stat;                // statistics override (if defined)
 
   // sizes
-  size_t memory;                   // number of bytes in arena+stack memory
+  mjtSize memory;                  // number of bytes in arena+stack memory
   int nemax;                       // max number of equality constraints
   int nuserdata;                   // number of mjtNums in userdata
   int nuser_body;                  // number of mjtNums in body_user
@@ -184,7 +184,7 @@ typedef struct mjSpec_ {           // model specification
   int nkey;                        // number of keyframes
   int njmax;                       // (deprecated) max number of constraints
   int nconmax;                     // (deprecated) max number of detected contacts
-  size_t nstack;                   // (deprecated) number of mjtNums in mjData stack
+  mjtSize nstack;                  // (deprecated) number of mjtNums in mjData stack
 
   // global data
   mjString* comment;               // comment at top of XML

include/mujoco/mjtnum.h

@@ -15,6 +15,8 @@
 #ifndef MUJOCO_INCLUDE_MJTNUM_H_
 #define MUJOCO_INCLUDE_MJTNUM_H_
 
+#include <stdint.h>
+
 //---------------------------------- floating-point definition -------------------------------------
 
 // floating point data type and minval
@@ -34,4 +36,10 @@ typedef unsigned char mjtByte;    // used for true/false
 
 
 
+//-------------------------------------- size definition -------------------------------------------
+
+typedef uint64_t mjtSize;         // used for buffer sizes
+
+
+
 #endif  // MUJOCO_INCLUDE_MJTNUM_H_