anchor.diff:  
     210 continue
   c     # zero-order extrapolation:
  -      do 215 m=1,meqn
  -         do 215 ibc=1,mbc
  -            do 215 j = 1-mbc,my+mbc
  +      do m=1,meqn
  +         do ibc=1,mbc
  +            do j = 1-mbc,my+mbc
                  q(mx+ibc,j,m) = q(mx,j,m)
  -  215       continue
  +            end do
  +         end do
  +      end do
         go to 299
   
     220 continue
   c     # periodic:
  -      do 225 m=1,meqn
  -         do 225 ibc=1,mbc
  -            do 225 j = 1-mbc, my+mbc
  -               q(mx+ibc,j,m) = q(ibc,j,m)
  -  225       continue
  +      write(6,*) 'clawpack4.6_bc2_default : ', 
  +     &            'Periodic BCs should not be set in bc2'
  +      stop
         go to 299
   
     230 continue
   c     # solid wall (assumes 2'nd component is velocity or momentum in x):
  -      do 235 m=1,meqn
  -         do 235 ibc=1,mbc
  -            do 235 j = 1-mbc, my+mbc
  +      do m=1,meqn
  +         do ibc=1,mbc
  +            do j = 1-mbc, my+mbc
                  q(mx+ibc,j,m) = q(mx+1-ibc,j,m)
  -  235       continue
  -c     # negate the normal velocity:
  -      do 236 ibc=1,mbc
  -         do 236 j = 1-mbc, my+mbc
  +            end do
  +         end do
  +      end do
  +c     # negate the normal velocity:
  +      do ibc=1,mbc
  +         do j = 1-mbc, my+mbc
               q(mx+ibc,j,2) = -q(mx+1-ibc,j,2)
  -  236    continue
  +         end do
  +      end do
         go to 299
   
     299 continue
  
positive.code: c
    110 continue
  c     # zero-order extrapolation:
        do 115 m=1,meqn
           do 115 ibc=1,mbc
              do 115 j = 1-mbc,my+mbc
                 q(1-ibc,j,m) = q(1,j,m)
    115       continue
        go to 199
  
    120 continue
  c     # periodic:
        do 125 m=1,meqn
           do 125 ibc=1,mbc
              do 125 j = 1-mbc, my+mbc
                 q(1-ibc,j,m) = q(mx+1-ibc,j,m)
    125       continue
        go to 199
  
    130 continue
  c     # solid wall (assumes 2'nd component is velocity or momentum in x):
        do 135 m=1,meqn
           do 135 ibc=1,mbc
              do 135 j = 1-mbc, my+mbc
                 q(1-ibc,j,m) = q(ibc,j,m)
    135       continue
  c     # negate the normal velocity:
        do 136 ibc=1,mbc
           do 136 j = 1-mbc, my+mbc
              q(1-ibc,j,2) = -q(ibc,j,2)
    136    continue
        go to 199
  
    199 continue
  
negative.code: c
    310 continue
  c     # zero-order extrapolation:
        do m=1,meqn
           do jbc=1,mbc
              do i = 1-mbc,mx+mbc
                 q(i,1-jbc,m) = q(i,1,m)
              end do
           end do
        end do
        go to 399
  
    320 continue
  c     # periodic:
        write(6,*) 'clawpack4.6_bc2_default : ', 
       &            'Periodic BCs should not be set in bc2'
        stop
        go to 399
  
    330 continue
  c     # solid wall (assumes 3'rd component is velocity or momentum in y):
        do m=1,meqn
           do jbc=1,mbc
              do i = 1-mbc,mx+mbc
                 q(i,1-jbc,m) = q(i,jbc,m)
              end do
           end do
        end do
  c     # negate the normal velocity:
        do jbc=1,mbc
           do i = 1-mbc, mx+mbc
              q(i,1-jbc,3) = -q(i,jbc,3)
           end do
        end do
        go to 399
  
    399 continue
  