[Octave-bug-tracker] [bug #50561] 350X slower code for eps() written in C++ rather than an m-file

[Rik]

Follow-up Comment #6, bug #50561 (project octave):

I had already tried one optimization which was to declare min_double outside
the loop.


double min_double = std::numeric_limits<double>::min ();


This didn't seem to make any difference.  Maybe because the value there is
declared as a const and can be resolved at compile time.

I also tried substituting a function call


  epsval(i) = pow (2.0, -1074e0);


with a constant


  epsval(i) = 4.940656458412465e-324;


This made no difference either.  For test input I used


x = zeros (1e7, 1);


so the only path that was executed was the assignment above.  I was surprised
by that one, but that's why you have to benchmark because human intuition can
be faulty.








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