CODE >R 1 chkPS,
    BP INCx, BP INCx, [BP] 0 POP[w]+,
;CODE NOP, NOP, NOP,
CODE R>
    [BP] 0 PUSH[w]+, BP DECx, BP DECx,
;CODE
CODE 2>R
    [BP] 4 POP[w]+, [BP] 2 POP[w]+, BP 4 ADDxi,
;CODE
CODE 2R> 2 chkPS,
    [BP] -2 PUSH[w]+, [BP] 0 PUSH[w]+, BP 4 SUBxi,
;CODE