[Octave-bug-tracker] [bug #38085] image package: fails to build with --enable-64

[Jordi Gutiérrez Hermoso]

Follow-up Comment #7, bug #38085 (project octave):

The line numbers don't seem to match what I see in __spatial__.cc at revision
faa0a913015f. Regardless, the problem seems to be with the following
function:


template <class ET, class MT, class ET_OUT>
ET_OUT entropy_filt (MT &vals, octave_idx_type len, int nbins)
{
  ET add;
  get_entropy_info<ET> (add, nbins);
  
  // Compute histogram from values
  ColumnVector hist (nbins, 0);
  for (octave_idx_type i = 0; i < len; i++)
    hist (vals (i) + add) ++;
  for (octave_idx_type i = 0; i < len; i++)
    hist (vals (i) + add) /= (double)len;
    
  // Compute entropy
  double entropy = 0;
  for (octave_idx_type i = 0; i < nbins; i++)
    {
      const double p = hist (i);
      if (p > 0)
        entropy -= p * xlog2 (p);
    }

  return entropy;
}


A first weirdness is that it's templating the return value ET_OUT, yet it's
always returning a double. I think the template argument ET_OUT is probably
unnecessary, or else entropy should be changed to type ET_OUT so that it can
use both float and double types.

As to the actual bug, I assume the problem is that `vals (i) + add` is
returning octave_int8 values, but those can't be used for indexing. I don't
even know why this used to work. I can't see what conversion path was used
when octave_idx_type was int.

I think a simple fix might be to change those lines to


hist ((vals (i) + add).value ()) ++;


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