ahay/src/authoring-sf-programs-f77

When to use

Use this skill for Madagascar processing programs in Fortran 77 fixed-format (file extension .f, program named M<Name>.f). Typical scenarios: maintaining legacy fixed-format code, porting existing F77 algorithms, or working with research groups that standardize on gfortran -std=legacy or ifort.

F77 vs F90 key differences:

For shared conventions (SConstruct rules, self-doc headers, naming) see skills/authoring-sf-programs/.

Skeleton

Minimal F77 program derived from api/f77/Testfile.f and api/f77/test/clip.f. Columns 1-6 are reserved; statement body starts at column 7; continuation marker goes in column 6.

C     Mclip.f  --  clip float data to +/- clip
      program Clipit
      implicit none
      integer*8 in, out
      integer*8 sf_input, sf_output, sf_leftsize
      logical sf_getfloat, sf_histint
      integer n1, n2, i1, i2
      real clip, trace(1000)
 
      call sf_init()
      in  = sf_input("in")
      out = sf_output("out")
 
      if (.not. sf_histint(in,"n1",n1))
     &    call sf_error("No n1= in input")
      if (.not. sf_getfloat("clip",clip))
     &    call sf_error("Need clip=")
      n2 = sf_leftsize(in,1)
 
      do 10 i2=1, n2
         call sf_floatread(trace, n1, in)
         do 20 i1=1, n1
            if (trace(i1) .gt.  clip) trace(i1) =  clip
            if (trace(i1) .lt. -clip) trace(i1) = -clip
 20      continue
         call sf_floatwrite(trace, n1, out)
 10   continue
      stop
      end

Column layout reminder:

123456789...
C     comment (C in col 1)
      statement (col 7+)
     &continuation (col 6)
 10   label (cols 1-5)

API cheat sheet

All calls go through the librsff wrapper (fortran.c + cfortran.h). Functions returning a value must be declared with the appropriate Fortran type.

Init and file handles — declare file handles as integer*8:

History reads — declare as logical; .false. means key absent:

History writes (call subroutines, no return value):

Command-line param reads — declare as logical; .true. if key found:

Data I/O (call subroutines):

Utility:

Build integration

The F77 API builds only when f77 appears in the SCons API list (api/f77/SConstruct):

1. Detects compiler via env.get('F77'); sets -DGFORTRAN or

-DINTEL_COMPILER accordingly.

1. Compiles fortran.c (with cfortran.h) into fortran.o.
2. Bundles into librsff.a (static library) and installs to lib/.
3. User programs link against both librsff and core librsf.

Typical user SConstruct snippet:

env.Append(LIBS=['rsff', 'rsf'])
env.Program('sfclip', ['Mclip.f'])
# For strict fixed-format:
env.Replace(F77FLAGS='-std=legacy -ffixed-form')

cfortran.h handles name-mangling: gfortran (single underscore) vs f2c-style (double underscore) via compile-time defines.

Pointers

Files in /Users/jgoai/m8r/src/api/f77/:

Shared conventions

General Madagascar conventions (self-documentation strings, parameter help, SCons Program builder, installation targets) are in:

skills/authoring-sf-programs/

F77-specific reminders:

• Declare sf_input, sf_output, sf_leftsize, sf_filesize as integer*8

— file handles and offsets are 64-bit on modern systems.

• Declare param-query functions (sf_getint, sf_histfloat, …) as logical

to test them in if (.not. …) guards.

• Use implicit none — F77 implicit typing silently maps i-n to integer

and the rest to real, hiding declaration bugs.

• Continuation: place the continuation character in column 6 only.