Thank you very much, petz!
I use your example file for run VEX in 64-bit mode, as described in http://www.sidefx.com/docs/houdini/hom/hou/runVex.html
It works, so in houdini 17, i can print a long value, calculated in VOP SOP, without overflow!
test_precision=64_.hipnc
(sorry, it's not commented, for comments please see petz's example)