Avoid unnecessary copies after of mju_mulQuat.

Since fdbbc8bbe0, mju_mulQuat allows in-place computations.
There were a few places where the result was unnecessarily assigned to a temporary variable.

PiperOrigin-RevId: 477746005
Change-Id: I7351ef4796e7d70a4a54b930037bfaadee781f12

src/engine/engine_core_smooth.c

@@ -35,7 +35,7 @@
 // forward kinematics
 void mj_kinematics(const mjModel* m, mjData* d) {
   mjtNum pos[3], quat[4], *bodypos, *bodyquat;
-  mjtNum qloc[4], qtmp[4], vec[3], vec1[3], xanchor[3], xaxis[3];
+  mjtNum qloc[4], vec[3], vec1[3], xanchor[3], xaxis[3];
 
   // set world position and orientation
   mju_zero3(d->xpos);
@@ -124,8 +124,7 @@ void mj_kinematics(const mjModel* m, mjData* d) {
           }
 
           // apply rotation
-          mju_mulQuat(qtmp, quat, qloc);
+          mju_mulQuat(quat, quat, qloc);
-          mju_copy4(quat, qtmp);
 
           // correct for off-center rotation
           mju_sub3(vec, xanchor, pos);

src/engine/engine_sensor.c

@@ -90,8 +90,7 @@ static void add_noise(const mjModel* m, mjData* d, mjtStage stage) {
         // quaternion
         else if (m->sensor_datatype[i]==mjDATATYPE_QUATERNION) {
           // apply quaternion rotation to quaternion, assign
-          mju_mulQuat(res, d->sensordata+adr, quat);
+          mju_mulQuat(d->sensordata+adr, d->sensordata+adr, quat);
-          mju_copy4(d->sensordata+adr, res);
         }
 
         // unknown datatype

src/engine/engine_util_solve.c

@@ -493,8 +493,7 @@ int mju_eig3(mjtNum* eigval, mjtNum* eigvec, mjtNum quat[4], const mjtNum mat[9]
     mju_normalize4(tmp);
 
     // accumulate quaternion rotation
-    mju_mulQuat(tmp+4, quat, tmp);
+    mju_mulQuat(quat, quat, tmp);
-    mju_copy4(quat, tmp+4);
     mju_normalize4(quat);
   }
 
@@ -512,8 +511,7 @@ int mju_eig3(mjtNum* eigval, mjtNum* eigvec, mjtNum quat[4], const mjtNum mat[9]
       tmp[0] = 0.707106781186548;     // mju_cos(pi/4) = mju_sin(pi/4)
       tmp[1] = tmp[2] = tmp[3] = 0;
       tmp[(j1+2)%3+1] = tmp[0];
-      mju_mulQuat(tmp+4, quat, tmp);
+      mju_mulQuat(quat, quat, tmp);
-      mju_copy4(quat, tmp+4);
       mju_normalize4(quat);
     }
   }

src/engine/engine_util_spatial.c

@@ -240,9 +240,8 @@ void mju_quatIntegrate(mjtNum quat[4], const mjtNum vel[3], mjtNum scale) {
   mju_copy3(tmp, vel);
   angle = scale * mju_normalize3(tmp);
   mju_axisAngle2Quat(qrot, tmp, angle);
-  mju_mulQuat(tmp, quat, qrot);
+  mju_mulQuat(quat, quat, qrot);
-  mju_normalize4(tmp);
+  mju_normalize4(quat);
-  mju_copy4(quat, tmp);
 }
 
 

src/engine/engine_vis_interact.c

@@ -374,7 +374,7 @@ void mjv_moveCamera(const mjModel* m, int action, mjtNum reldx, mjtNum reldy,
 void mjv_movePerturb(const mjModel* m, const mjData* d, int action, mjtNum reldx,
                      mjtNum reldy, const mjvScene* scn, mjvPerturb* pert) {
   int sel = pert->select;
-  mjtNum forward[3], vec[3], dif[3], scl, q1[4], q2[4], xiquat[4];
+  mjtNum forward[3], vec[3], scl, q1[4], xiquat[4];
 
   // get camera info and align
   mjv_cameraInModel(NULL, forward, NULL, scn);
@@ -394,8 +394,7 @@ void mjv_movePerturb(const mjModel* m, const mjData* d, int action, mjtNum reldx
 
     // make quaternion and apply
     mju_axisAngle2Quat(q1, vec, scl*mjPI*2);
-    mju_mulQuat(q2, q1, pert->refquat);
+    mju_mulQuat(pert->refquat, q1, pert->refquat);
-    mju_copy4(pert->refquat, q2);
     mju_normalize4(pert->refquat);
 
     // compute xiquat
@@ -404,10 +403,12 @@ void mjv_movePerturb(const mjModel* m, const mjData* d, int action, mjtNum reldx
     // limit rotation relative to selected body
     if (sel>0 && sel<m->nbody) {
       // q2 = neg(selbody) * refquat
+      mjtNum q2[4];
       mju_negQuat(q1, xiquat);
       mju_mulQuat(q2, q1, pert->refquat);
 
       // convert q2 to axis-angle
+      mjtNum dif[3];
       mju_quat2Vel(dif, q2, 1);
       scl = mju_normalize3(dif);