implementation in code of G64 Pxxx value

Hi -
     I'm hoping someone knows where in the motion code the code implements the move-blending parameter G64 Pxxx.  I'm running a milling machine with the Vital Systems motenc interface under version 2.8.4.  I'm having trouble with both G61 and G64.  I can't see as they make any difference at all.  I would like to dive into the code and see how the Pxxx value is handled.
     Thanks in advance.

It's almost certainly in here; github.com/LinuxCNC/linuxcnc/blob/master/src/emc/tp/tp.c

But won't be referenced as G64, it will be a blend tolerance or similar.