The Fortran-90 files in this directory were generated from the original
HTDP v3.2.5 source code (htdp.for) using the fsplit utility, included
with NetBSD:

http://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/usr.bin/fsplit/

Only the subroutines necessary for displacement and velocity
calculations are included. The following subroutines are called from C:

IYMDMJ, MODEL, NEWCOR, PREDV, SETRF, SETTP

The following subroutines have been patched to replace Fortran I/O
(WRITE and STOP statements) with R-only versions of error and warning
(REXIT, RWARN) as required by CRAN:

COMVEL, PLATVL, POLYIN, VTRANF, VTRANF_IERS, XTO08

REXIT and RWARN are defined in src/main/xxxpr.f in the R sources. These
subroutines should be replaced for any other use of the HTDP library.
See the following commit for details:

https://github.com/jbuonagurio/RHTDP/commit/28f1bdfcfb86d1527ce2ef050095975cf0fa9233

All other subroutines are generally unmodified from the original source,
however the nonstandard type declaration INTEGER*4 has been changed to
the Fortran 90 equivalent INTEGER(KIND=4).

A sample makefile is included to build a DLL, as well as a sample
calculation in 'example.c'. 'rexit.f' contains a stub for the REXIT
subroutine and should be replaced.
