[Octave-bug-tracker] [bug #63444] "if (COND)" is much slower than "if (all (COND))"

[Rik]

Follow-up Comment #6, bug #63444 (project octave):

I made another octfile which tests how much time the test for isnan() adds. 
It turns out that this seems to be a bigger portion of the slowdown (20%) than
the actual loopisg structure (1x or 2x).

The file is shown below and attached as loop_tst_nan.cc


#include <octave/oct.h>

DEFUN_DLD (loop_tst_nan, args, nargout,
           "Test single or double loop equivalent to all()\n"
           "ARG1 : TRUE/FALSE, test for NaNs?\n"
           "ARG2 : numeric array")
{
  if (args.length () != 2)
    print_usage ();

  bool do_nan_test = args(0).bool_value ();
  NDArray A = args(1).array_value ();
  octave_idx_type N = A.numel ();
  bool retval = true;

  if (do_nan_test)
    {
      for (octave_idx_type i = 0; i < N; i++)
        {
          if (std::isnan (A(i)))
            error ("loop2: Can not convert NaN to logical value");
          if (! A(i))
            retval = false;
        }
    }
  else
    {
      for (octave_idx_type i = 0; i < N; i++)
        {
          if (! A(i))
            retval = false;
        }
    }

  return ovl (retval);
}


Results are


octave:4> tic; for i = 1:100, loop_tst_nan (0,x); end; toc
Elapsed time is 0.301775 seconds.

octave:9> tic; for i = 1:100, loop_tst_nan (1,x); end; toc
Elapsed time is 0.383141 seconds.




(file #54040)

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Additional Item Attachment:

File name: loop_tst_nan.cc                Size:0 KB
    <https://file.savannah.gnu.org/file/loop_tst_nan.cc?file_id=54040>



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