performance: don't recompute rpn values already in the cache
performance: don't recompute rpn values already in the cache

mkeilman/sirepo,mkeilman/sirepo,mrakitin/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,mrakitin/sirepo,radiasoft/sirepo,radiasoft/sirepo,mrakitin/sirepo