A first try at de-obfuscate the structure, mainly in ./loessf.f :

  ehg182(): warning(message) generator, defined in ./loessc.c
	    called from almost any non-trivial function in loessf.f
	    and hence *NOT* in the following calling structure


loess()		        [R] ../R/loess.R
|
\-> simpleLoess()	[R]
    |
    |-> loess_raw	      loessc.c
    |	 |
    |	 |--> lowess_workspace   "
    |	 |    |
    |	 |    \--> lowesd
    |	 |
    |	 |
    |	 |--> lowesf
    |	 |    |
    |	 |    \--> ehg136
    |	 |         |
    |	 |         \--> ehg127	{fit at one new x}
    |	 |              |
    |	 |              |--> ehg106	{partial sort (for median etc)}
    |	 |              |
    |	 |              |--> "LINPACK" [QR,SVD..]
    |	 |              |
    |    |              \--> ehg184	{warning}
    |	 |
    |    |
    |	 |
    |	 |
    |	 |
    |	 |
    |	 |--> lowesb
    |    |    |
    |    |    |--> ehg183		{warning}
    |    |    |
    |    |    \--> ehg131
    |    |         |
    |    |         \--> ehg139
    |    |              |
    |    |              |--> ehg127  [see above]
    |    |              |
    |    |              \--> ehg137
    |	 |
    |
    |
    |
    |-> loessp






predict.loess() 	[R] ../R/loess.R
|
\-> predLoess()		[R]
    |
    \-> loess_raw	      loessc.c

smooth.spline()  [R]
 |
 \--> rbart() [ = C_rbart() ]           src/qsbart.f
      |
      \--> sbart()                      src/sbart.c
           |--> sgram()                 src/sgram.f
           |    |--> interv()           src/bvalue.f
           |    \--> bsplvd()           src/bsplvd.f
           |         \--> bsplvb()          "
           |--> stxwx()                 src/stxwx.f
           |    |--> interv()             (see above)
           |    \--> bsplvd()               "
           |         \--> bsplvb()          "
           \--> sslvrg()                src/sslvrg.f
                |--> sinerp()           src/sinerp.f
                |--> bvalue()           src/bvalue.f   (above)
                |    \--> interv()        (see above)
                |--> interv()               "
                |--> bsplvd()               "
                |    \--> bsplvb()          "
                |--> dpbfa()            ../../appl/dpbfa.f  {LINPACK}
                \--> dpbsl()            ../../appl/dpbsl.f


predict.smooth.spline()  [R]
 |
 \--> bvalus()                          src/bvalus.f
       \--> bvalue()                    (see above)
             \--> interv()                "


-------------

But note that both supsmu() and ppr() also call on smoothing splines :

supsmu() [R]
 |
 |-> setsmu				src/ppr.f
 \-> supsmu                               "
     |
     |--> smooth                          "
     \--> spline                          "
          |
          |- intpr()
          |- dblepr()
          |- bdrsplerr()                src/ksmooth.c
          |
          \- rbart()                    (see above)
             \-> sbart()  .....etc..... (see above)



ppr()   [R]
 |
 |-> setppr				src/ppr.f
 |
 |-> pppred				  "
 |   \-> fsort                            "
 |       \-> sort                         "
 |
 \-> smart                                "
     \-> smart1                           "
         |
         |-> sort			(see above)
         |
         |-> subfit                       "
         |   |
         |   |-> newb
         |   |
         \---+-> fulfit
             |   |
             |   v
             \-> onetrm
                 |
                 \-> oneone
                     |
                     |--> supsmu	(see above)
                     |--> sort		(see above)
                     |
                     |--> pprdir
                     |    \-> ppconj
                     |
                     \--> pprder
                          \-> pool


predict.ppr() [R]
 |
 pppred					(see above)

-------

Note that CRAN package "mda" also relies on these (identical) six files :

bsplvd.f bvalue.f
sgram.f sinerp.f sslvrg.f stxwx.f