[SciPy-Dev] f2py, the fortran integer type, and npy_intp
Mon Jul 12 11:10:04 CDT 2010
On Sat, Jul 10, 2010 at 6:33 PM, Sturla Molden <firstname.lastname@example.org> wrote:
> Charles R Harris skrev:
>> I don't think the bindings don't help, we need to have the default
>> integers in the existing pre-FORTRAN77 code in scipy compiled as
>> Py_ssize_d, and then f2py needs to be modified to generate appropriate
>> Python bindings. That's a lot of work. Even with the bindings I think
>> one would need to have a script to rewrite the FORTRAN code since the
>> c-type corresponding to Py_ssize_d isn't fixed.
> We should also beware that the problem applies to real numbers as well
> as integer. You cannot rely on standard mappings from C float to REAL
> and C double to DOUBLE PRECISION.
> With pre-Fortran 90, there is no way of controlling this portably. With
> Fortran 90 and later, we have the standard methods selected_real_kind
> and selected_int_kind that returns (compiler dependent) "kind" numbers,
> which can be used to declare real and integers with specific precitions.
> integer, parameter :: single = selected_real_kind(p=6, r=37)
> integer, parameter :: double = selected_real_kind(p=13)
> integer, parameter :: npy_int8 = selected_int_kind(2)
> integer, parameter :: npy_int16 = selected_int_kind(4)
> integer, parameter :: npy_int32 = selected_int_kind(9)
> integer, parameter :: npy_int64 = selected_int_kind(18)
> Now we can declare an npy_int32 like this:
> integer(kind=npy_int32) :: i
> Still we have no ide what npy_intp would map to. We can do this in
> Fortran 2003:
> use, intrinsic :: iso_c_binding
> integer, parameter :: npy_intp = c_intptr_t
Trouble is that 'c_intptr_t' isn't defined for some fortran compilers.
So you first have to find which one of 'int', 'long int' or 'long
long int' corresponds to 'npy_intp' in C code, then declare a
parameter in fortran:
integer, parameter :: fort_npy_intp = c_long
for example. Not a big deal.
> integer(kind=npy_intp) :: i
> Real numers and other integer sre also easier:
> integer, parameter :: float = c_float
> integer, parameter :: double = c_double
> integer, parameter :: npy_int32 = c_int32_t
> Such declarations can be put in a module, and subsequently imported to
> Fortran 90.
> It might be that f2c is the only cure for old Fortran code. The other
> option is to write a Fortran 2003 wrapper to interface C. Then this
> wrapper will call the old Fortran code. We then need to declare the old
> Fortran routine (as an interface block) to Fortran 2003. The Fortran
> compiler is then smart enough to do the correct conversions, including
> making a local copy of an array if that is needed.
Umm, unless I misunderstand you, this isn't how many fortran compilers
behave (ifort, gfortran & g95).
Try the following:
integer(kind=8) :: arr(10,10)
integer(kind=4), intent(inout) :: arr(:,:)
arr = 1
Compiling with gfortran 4.4.4:
Error: Type mismatch in argument 'arr' at (1); passed INTEGER(8) to INTEGER(4)
But perhaps I misunderstand you.
> Wasn't Kurt Smith working on this for a GSOC project?
It is coming along, and being actively developed. Many niggling
issues to work out. We're at near-parity with f2py at the moment,
with a few enhancements, but no 'pyf' interface modules (yet).
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