navfn ros priority blocks

edit

As code shows below, i do not understand the const 'INVSQRT2' and the variable 'curT',what do they play roles in code,how can i understand them

#define INVSQRT2 0.707106781

  float le = INVSQRT2*(float)costarr[n-1];
  float re = INVSQRT2*(float)costarr[n+1];
  float ue = INVSQRT2*(float)costarr[n-nx];
  float de = INVSQRT2*(float)costarr[n+nx];


  if (pot < curT)   // low-cost buffer block
  {
      if (l > pot+le) {
              push_next(n-1);
      }
      if (r > pot+re)
      {
              push_next(n+1);
      }
      if (u > pot+ue)
      {

              push_next(n-nx);
      }
      if (d > pot+de)
      {
              push_next(n+nx);
      }
  }
  else
  {
      if (l > pot+le) {

              push_over(n-1);
      }
      if (r > pot+re)
      {
              push_over(n+1);
      }
      if (u > pot+ue)
      {

              push_over(n-nx);
      }
      if (d > pot+de)
      {

              push_over(n+nx);
      }
  }