void xf_xfmvect( FVECT vnew, FVECT vold )
void xf_rotvect( FVECT nnew, FVECT nold )
double xf_scale( double sold )
The xf_xfmvect routine applies the current transformation to the vector vold, scaling and rotating it to its proper location, which is put in vnew. The only difference between xf_xfmpoint and xf_xfmvect is that in the latter, the final translation is not applied.
The xf_rotvect routine rotates the vector nold using the current transformation, and stores the result in nnew. No translation or scaling is applied, which is the appropriate action for surface normal vectors for example.
The xf_scale function takes a scalar argument sold and applies the current scale factor, returning the result.