Re: Rethinking octave_idx_type

[John W. Eaton]

On 11/28/2016 07:54 AM, John W. Eaton wrote:

> The first step is to use F77_INT instead of octave_idx_type to declare
> integer variables that are passed to Fortran functions.

We can also get some help from GCC to identify where there are issues 
when working on this step.

If we define F77_INT to be 32 bits wide and octave_idx_type to be 64 
bits wide and compile with -Wconversion, we should see errors anywhere 
there are pointer mismatches and warnings about passing octave_idx_type 
where F77_INT is expected.  See the attached program, for example.  I 
know from experience that -Wconversion leads to a LOT of noise in the 
output from the compiler when building Octave, but the warnings from 
recent versions of GCC use the typedef names so it should be easy to 
filter the messages and find only the places where F77_INT is affected.

We should already be using F77_INT for the function declarations of any 
Fortran code used by Octave so it should be fairly straightforward to 
find all the locations that are affected.

Then we need a function to convert octave_idx_type to F77_INT and check 
for possible overflow.  For example, to safely extract the number of 
rows from a matrix that will be passed to a Fortran subroutine we would 
use something like this

  // May error if A is too large for our Fortran libraries.
  F77_INT nr = to_f77_int (A.rows ());

instead of just

  F77_INT nr = A.rows ();

jwe

sizes.cc
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