sf_stack_top
stack[PF_ANCHOR_STACK_MAX].sf_stack_top = &stack[0];
top_sf = stack[PF_ANCHOR_STACK_MAX].sf_stack_top;
stack[PF_ANCHOR_STACK_MAX].sf_stack_top = top_sf;
stack[PF_ANCHOR_STACK_MAX].sf_stack_top = top_sf;
sf[PF_ANCHOR_STACK_MAX].sf_stack_top = &sf[0];