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

[Dan Sebald]

Follow-up Comment #7, bug #50561 (project octave):

What assignment above are you referring to?  Looking at the whole routine, I
see now that

"retval = epsval"

is actually a large array assignment.  So clearly that was a huge reassignment
of an array every time in the loop.

Did you try the things you mention before making the retval = epsval move? 
After that retval=epsval move, maybe the more granular details you listed will
now start to make a difference, improving things even further.

Also, if this retval is a large array, stack construct, does the C++ compiler
optimize that out?  Or would it make sense to rather than assign retval =
epsval, do things more direct with:


          return epsval;
[snip]
              return epsval;
[snip]
    return fill_matrix (args, std::numeric_limits<double>::epsilon (),


?

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