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TPFort v 1.82 - A link from Turbo Pascal 5.0-6.0 to MS Fortran 5.0 or 5.1.

Copyright (c) 1989,1990,1991 D.J. Murdoch.  All rights reserved.
Portions copyright (c) TurboPower Software.  Used with permission.


PURPOSE

TPFort is a collection of several procedures that allow Microsoft Fortran
routines to be called from Turbo Pascal.  I wrote it so that I could use the
binary-only NAG Fortran library for numerical routines in Turbo Pascal
programs, but it ended up being a general purpose linker.


PRICE

TPFort is free to use and incorporate into your own programs for any purpose.
Distribute it to anyone you like, but please don't remove my copyright notice.
If you modify it in any way, please do not distribute the modified version.
Full source code is included.


METHOD

The Fortran routines are compiled into their own loader file which is loaded at
run time by a Turbo Pascal program, making most of the Fortran subroutines and
functions available to the Pascal program.  The molasses-slow Fortran compiler
and linker need only be run once to create the loader; changes to the Pascal
part of the program don't force recompiling or re-linking of the Fortran part.

The Fortran loader will be loaded at the top of the TP heap.  The program
NEEDMEM is provided to print out the memory requirements of the loader. If the
total required is greater than TP's MaxAvail, TPFORT won't run.


INSTRUCTIONS

There are several steps involved in preparing Fortran routines to be called
from Turbo Pascal.

1.   Preparing the Fortran Program

Write a Fortran program which includes the following declarations and a call
to CALLTP, in the following format:

        EXTERNAL routine1, routine2, ..., routineX

        CALL CALLTP(routine1, routine2, ..., routineX, X)

where routine1 through to routineX are the names of the Fortran routines you
wish to make available to your Turbo Pascal program, and X is an integer value
giving the number of routines being passed.  The external declaration is
extremely important; if not given, Fortran will assume the routine names are
local integer or real variables, and things will get really messed up.

This loader may do anything else, such as reading data from files, allocating
space, etc.  It's not all that important where the call to CALLTP takes place,
but more efficient use will be made of the program stack if the call comes
somewhere in the main program, rather than in a function or subroutine.

After this call and any other initialization necessary, the program should
exit.  As this will close any open files, and I/O done while TP is active
is probably unreliable, it should complete any I/O operations before quitting,
and the routines being passed should avoid doing I/O.

Compile this routine and link it to the object file CALLTP.OBJ.  I've only
tested TPFORT with the default large memory model, but it should work in the
huge model as well.  It won't work in the medium model, because TPFORT expects
full 4 byte addresses.

NB:  With version 5.1 of the Fortran compiler, the loader routine (and possibly
     others) MUST be compiled with the /Gb option for backward compatibility.
     If not, programs will crash on the first call.

I recommend using the /FPi87 floating point option, to get the smallest code,
but if you don't have a coprocessor you'll need /FPi or one of the other /FP
options.  (It would be safe to use /FPi87 even if you don't have a
coprocessor, if you link the TP emulator in, but I don't think the Fortran
startup code will run if you don't.)

Be sure to specify to the linker that a larger than normal stack will be
needed - I'd suggest a minimum of 16K. The Turbo Pascal program will be using
this stack instead of its own much of the time, and TP makes much heavier use
of the stack than does Fortran.

Warning:  Don't try running the loader program on its own, unless you avoid
executing the call to CALLTP.  If TP isn't there to catch that call, you're
very likely to crash.  It might be a good idea to rename the .EXE with a non-
executable extension such as .LDR just to be sure.

2.   Preparing the TP dummy procedures

You need to create dummy versions of all the Fortran routines that you want to
call.  They _must_ be declared as "far" routines, either through the use of
the $F+ compiler directive, or by putting them in the interface section of a
unit.  I'd suggest isolating all of them into their own unit and interfacing
them.

Each of the dummy routines takes an argument list that corresponds exactly to
the argument list of the Fortran routine.  By default, all Fortran arguments
are passed by reference, so these should be too, by declaring them as "var"
parameters.  The following list gives corresponding types between the two
languages:

  Fortran               TP

  INTEGER*2             integer
  INTEGER*4             longint
  INTEGER               longint
  REAL                  single
  REAL*4                single
  REAL*8                double
  DOUBLE PRECISION      double
  CHARACTER*n           (special - see note below)
  CHARACTER*(*)         (special - see note below)
  COMPLEX               fort_complex8
  COMPLEX*8             fort_complex8        These types will be declared in
  COMPLEX*16            fort_complex16       the FortLink unit someday
  LOGICAL               fort_logical
  EXTERNAL              (special - see note below)

Note also that Fortran and TP use different conventions for the order of
indices in multi-dimensional arrays.  For example, the Fortran array

  REAL X(10,20,30)

would be declared as

  x : array[1..30,1..20,1..10] of single;

in TP. Note also that TP (up to version 6.0, at least) has no facility for
variable dimensions on arrays:  to handle an array which is declared as X(N,M)
you have to declare X as a one-dimensional array and handle the indexing
yourself.

Thus a call to the NAG matrix inversion routine F01AAF with Fortran
declaration

 SUBROUTINE F01AAF(A, IA, N, UNIT, IUNIT, WKSPCE, IFAIL)
 INTEGER IA, N, IUNIT, IFAIL
 REAL*8 A(IA,N), UNIT(IUNIT,N), WKSPCE(N)

would be simulated with dummy declarations something like

 procedure f01aaf(var a:realarray;       { realarray is declared in the
                                           FortLink unit }
                  var ia, n:longint;
                  var unit:realarray;
                  var iunit:longint;
                  var wkspce:realarray;
                  var ifail:longint);

and element A(I,J) would be addressed at a[i+(j-1)*ia].

The content of the dummy TP routine is very simple, and should not be varied.
If the Fortran routine is a SUBROUTINE, use a definition like

  const
    f01aaf_num = 1;  { this is the position of F01AAF in the call to CALLTP }

  procedure f01aaf;
  begin
    callfort(f01aaf_num);
  end;

If desired, additional instructions can be put before the call to callfort;
however, no local variables may be declared and no instructions may follow the
call.

If the Fortran routine is a FUNCTION, what to do depends on the function's
type.  Fortran and TP agree on the convention for returning values up to 4
bytes (except singles/REAL*4), so callfort can be used for these functions.
The most common would be a Fortran INTEGER function being declared as a TP
longint function and using callfort.

However, Fortran and TP use different conventions for other return types, and
you need to use special calls to do the conversion. If the Fortran routine is
a REAL*8-valued FUNCTION, the "fdouble" procedure replaces callfort.  Use
"fsingle" for REAL*4 values.  For example, for the Gaussian random number
generator G05DDF, the Fortran declaration is

 REAL*8 FUNCTION G05DDF(A, B)
 REAL*8 A, B

and the TP declarations are

 function g05ddf(var a,b:double):double;

with implementation

 const g05ddf_num = 2;
 function g05ddf;
 begin
   fdouble(g05ddf_num);   { Note that this is a procedure! }
 end;

Other structured types can also be returned with some care.  You have to
declare the dummy function to be a pointer to the appropriate type, and use
the "fpointer(procnum)" call to the Fortran routine.  TPFORT only reserves
8 bytes of space for return values, but larger values can be returned with
some trickery as described in FORTLINK.DOC in the header for fpointer.


3.  Preparing the TP main program

Once you have your dummy procedure unit set up, you have to make some
modifications to the main program to link in the Fortran at run-time.
This is all done in a single call to

 function LoadFort(prog:string;TPentry:pointer):boolean;

The prog argument should contain a string giving the fully qualified name of
the Fortran program to be loaded; TPentry should give the address of a TP
routine taking no arguments, which is going to do all the calculations with
the Fortran routines.  It's necessary to do things this way because the call
to LoadFort switches over to the Fortran stack; TPentry^ and any routine it
calls must be able to execute there.  If LoadFort is successful, it won't exit
until TPentry^ returns, and it'll give a True return value.  If it fails
for some reason, it'll print a message and return a False value.  In this
case TPEntry^ wasn't executed at all.  It's possible to call LoadFort several
times if you want to switch in and out of "Fortran mode", though I don't know
any reason to do so.  Only the first time will load anything, but they'll all
attempt to switch to Fortran mode.  Be sure never to call a Fortran
routine when you're not in Fortran mode, or you're likely to crash (or at
least get garbage out). To help determine the current status, the FortLink
unit interfaces two variables:

  fortloaded     : boolean;    { True indicates Fortran routines are in memory }
  fortsafe       : boolean;    { True indicates you're in Fortran mode }

If you like, you can put tests of fortsafe into your dummy routines before
the callfort or fdouble calls, to abort if there's a problem.

If you want to reclaim the memory used by your loader, call UnloadFort
when you're *not* in Fortran mode.  If you call it in Fortran mode, the
call will be ignored.  You might want to use this feature to load
different Fortran libraries; only one may be loaded at a time.


PASSING STRINGS AND CHARACTER VARIABLES

In Turbo Pascal, the "string" type stores the current length in the first
byte.  MS Fortran doesn't have a corresponding type; however, it does allow
variable length character variables to be passed to a routine with the
"CHARACTER*(*)" declaration.  The way this is handled internally is
undocumented, as far as I know, but I've tried to make a guess and my tests
seem to work.

It appears that any time CHARACTER variables are passed as arguments to a
SUBROUTINE or FUNCTION, their lengths are stored in a table of word-sized
values.  A pointer to this table is stored at a fixed location, in the global
variable __fcclenv.  To give access to this table, FORTLINK sets up a
pointer to __fcclenv in the global Size_Table.

Thus, to pass CHARACTER variables to a Fortran routine, two extra steps are
necessary.  First, you have to construct a table of the current lengths of
each CHARACTER argument; second, you have to set __fcclenv to point to it.
Typical code to pass strings s1 and s2 to Fortran procedure UCHAR would be

 type
   my_length_rec = record
     dummy,     { I don't know what the first entry in the table is for }
     s1_length,
     s2_length : word;
   end;
 var
   my_lengths : my_length_rec;
   s1,s2 : string;

 begin
   with my_lengths do
   begin
     s1_length := length(s1);
     s2_length := length(s2);
   end;
   Size_Table^ := @my_lengths;    { Note the ^ and @ ! Size_Table itself
                                    should never be changed }

   Uchar(..{non character args}...,
         s1[1], ....{more non characters} ...,  { Skip the length byte! }
         s2[1], ....{etc.} );

In the TP declaration of Uchar, the character arguments could be type char, or
untyped.  The same sort of technique would be used to pass arrays of char to
Fortran.

As described below, it's also possible to have Fortran call TP procedures and
functions.  In this case, the TP procedure should save the sizes of any
character arguments just after Enter_Pascal is called; the Size_Table^ pointer
will be changed by any activity in Fortran at all. The length of the first
character argument will be in Size_Table^^[1]; others will be in appropriate
places in the array.

Note:  Because all of the above is undocumented by Microsoft, there may be
mistakes.  Test it carefully before you depend on it!


PASSING FUNCTION REFERENCES

It is possible to pass function or procedure references to a Fortran routine,
but it's a little tricky.

The Fortran setup is just the same as for any other kind of routine.  Just
pass the procedure name in CALLTP.

The dummy definition is much the same.  Declare the parameter which is the
routine being passed as type "extval", passed by value.

The main routine then calculates the reference extval using a call to
"fort_external(procnum)", where procnum is the number of a Fortran procedure
being passed, or "pas_external(@proc)", where proc is the TP procedure
being passed, and saves the answer in a temporary variable.  It passes this
variable to the dummy routine.

The main bug in this procedure is that fort_external and pas_external allocate
space for a pointer on the stack, and leave it there.  Thus you can't execute
them in the middle of an expression, or it will get messed up. You should call
the routine Clean_External as soon as possible after using the temporary
variable, to restore the stack to normal.  Call it once for each call you made
to fort_external or pas_external.  In a loop it's probably safe to calculate
the temporary once at the beginning and only clean it up once at the end.  You
MUST reassign the temporary variable every time you enter the routine that
uses it, because its value becomes worthless as soon as you call
Clean_external or exit.

There's another bug in pas_external - the TP routine will be executed fully in
the Fortran context.  In particular, this means all global references will
reference the wrong data segment, and TP is likely to overwrite registers that
Fortran expects to have preserved.  To fix this up, at the very beginning you
must call Enter_Pascal, and you must call Leave_Pascal just before exiting.
This temporarily restores the TP context, and saves some registers. Note that
stack checking has to be disabled in a routine being passed this way, since
the stack checker makes a reference to the global System.Stacklimit, and gets
executed before Enter_Pascal.

Calls back to Fortran routines are allowed.  Note that only dummy procedures
and functions defined with callfort may be recursive; functions using fsingle,
fdouble or fpointer can not be.  For example, if the Fortran REAL*8 FUNCTION
Minimizer gets passed the TP Myfunction to minimize, then Myfunction can't
call Minimizer, but it can call some other Fortran routine.  This isn't such a
large restriction though, because most Fortran routines don't allow recursive
calls anyways.  (Actually there's a way around this:  pass the Fortran
function through CALLTP several times.  If the Fortran routine could handle
recursive calls normally, then the separate dummy functions will be able to
call each other.)

It's also possible to call a routine that was passed in as an Extval:  use the
Ext_Pointer function to convert it into a procedure pointer, and call that.
For example, the following TP routine might be called from Fortran:

  procedure callit(routine:extval);
  type
    proc_type = procedure(i:integer);   { Declare a procedure type }
  var
    the_routine : ^proc_type;           { and a pointer to it }
  begin
    the_routine := ext_pointer(routine);   { Convert the extval to a pointer }
    the_routine^(5);                       { and call it with argument 5 }
  end;

This works well as long as the routine being passed is known to be a TP
routine.  If it's Fortran, you must "Leave_Pascal" before the call and
"Enter_Pascal" after it.  The catch is that once you Leave_Pascal, you won't
have access to the TP data segment.  Only local variables will be accessible.
If the function could be written in either language, it's probably safest to
assume Fortran, and be sure that any TP routine that might be passed uses the
Enter_Pascal and Leave_Pascal routines.  They're safe to use in any TP
routine, whether it's being called from TP or Fortran.

Note 1:  Leave_Pascal will only restore the Fortran context if Enter_Pascal
was used to save it.  This means you can't call a Fortran routine using the
Ext_Pointer pointer unless you're in a routine that was called by Fortran.  I
don't think this is a big restriction, however, since you wouldn't normally
need to use an Extval at all, unless you're dealing pretty closely with
Fortran.

Note 2: The method of passing routines works for TP functions only if they use
the same function-value passing convention as Fortran.  Effectively this means
only char, integer and longint valued functions may be passed. There's no way
to call most other TP functions, but it's possible to construct TP functions
which simulate any Fortran function.  Fortran expects the caller to allocate
temporary space for larger return values and expects the function to put the
value there.  So, to write a TP routine that looks to Fortran as though it has
the declaration

  REAL*8 FUNCTION SUMSQ(N,X)
  INTEGER N
  REAL*8 X(N)

write the header as follows:

 function sumsq(var n:longint; var x:realarray; { Mimic the Fortran parameters
                                                  first }
         value_ofs:word):double_ptr;     { Always add another word for the
                                           return address, and return a
                                           pointer. "double_ptr" is a
                                           pointer to a double declared in
                                           FortLink }

See the sample program for the rest of the details.


EXAMPLE

A sample program is contained in the following files:

  PSAMPLE.PAS           The TP source for the main program
  FSAMPLE.FOR           The MS Fortran source for the loader & routines
  FSAMPLE.PAS           The dummy definitions for FSAMPLE

Also included is a Borland style MAKEFILE that compiles both parts.

Warning:  There's a bug in MS Fortran 5.0 which means the sample program won't
run on some XT machines.  If you crash when you try to run it, read about the
problem and a patch to fix it in FORTRAN.BUG.


SUPPRESSING FORTRAN ERRORS

You can suppress many Fortran intrinsic errors by reprogramming the
coprocessor, but that doesn't always work. (This is a bug in MS Fortran,
not in TPFORT. MS gives no way to suppress some errors.) There's a
variable called _MERRQQ which appears to suppress the abort when set to
a non-zero value; FortErrorFlag is a pointer to it.

The MS Fortran 5.1 documentation claims to allow more control over errors than
was allowed in version 5.0.  I don't know if it works, or whether the method
above is still necessary.


LIMITATIONS

I had real doubts that Fortran I/O would work properly when called from TP,
but have successfully used it in several programs.  Still, I mistrust it.

Because Fortran keeps so much data in the stack segment, you might not be able
to increase the stack size large enough.


FILES

The following files should be included here:

MAKEFILE        A Borland style make file for the demo.  Just run MAKE.
TPFORT   DOC    This file
FSAMPLE  FOR    The demo Fortran source code
CALLTP   ASM    A86 source code for CALLTP
CALLTP   OBJ    The object code to be linked to the Fortran routine
FSAMPLE  PAS    The dummy definitions to access the Fortran code
PSAMPLE  PAS    The demo TP source code
FORTLINK PAS    Source to the main TPFORT unit
CALLFORT ASM    A86 source code for external routines in FORTLINK
CALLFORT OBJ    Object file for linking into FORTLINK.TPU
OPRO     INC    A few routines extracted (with permission) from the
                Object Professional library
FORTRAN  BUG    Description of a bug and a patch for MS FORTRAN 5.0
NEEDMEM  EXE    Program to determine memory requirements of Fortran loader


COMMENTS AND QUESTIONS

Send any comments and/or bug reports to me at one of the following addresses:

  Duncan Murdoch
  79 John St W
  Waterloo, Ontario, Canada
  N2L 1B7

  Internet:  [e-mail]
  Fidonet:   dj murdoch at 1:221/177.40
  Compuserve: 71631,122


SOURCE CODE

TPFORT is a mixture of Turbo Pascal and A86 assembler. A few Object
Professional routines have been included in the file OPRO.INC with the
kind permission of Kim Kokkonen, of TurboPower Software.  If you have
Object Professional, you can set the OPRO_VER compiler variable, and the
real OPro routines will be linked instead.

If you don't own Object Professional, leave OPRO_VER undefined and
OPRO.INC will be automatically included.  However, if you don't own
Object Professional you're really missing out; I'd suggest buying it.
You can contact TurboPower at 800-333-4160 or 719-260-6641 (voice),
719-260-7151 (fax), or by email to Compuserve ID 76004,2611 (that's
[e-mail] on Internet).


WARRANTY

There is no warranty of any kind with this program.  Use it for free; I hope
you get some value out of it.

RELEASE HISTORY

 1.82 -  Added OPRO.INC to distribution; added UnLoadFort procedure.
 1.81 -  Fixed MAKEFILE errors, added check for valid proc addresses
 1.8  -  Cleaned up memory management, added version tests and Loaderror
         variable and messages
 1.7  -  added FortErrorFlag
 1.6  -  saves coprocessor or emulator state before running Fortran loader
 1.5  -  corrected bugs, and added Ext_Pointer function
 1.4  -  corrected support for CHARACTER types
 1.3  -  fixed bug to allow large Fortran programs, added NEEDMEM program
 1.2  -  added support for floating point emulation.
 1.1  -  added support for limited recursion, and many function return types.
 1.0  -  first release.