sub TOLERANCE () { 1e-13 }

sub compare {
   my ($a, $b, $tol) = @_;
   $tol = TOLERANCE unless (defined($tol));
   my $diff = ($a - $b);
   if ($diff > +$tol) { return +1; }
   if ($diff < -$tol) { return -1; }
   return 0;
}

sub format_cmp {
   my ($cmp) = @_;
   if ($cmp <  0) {return "<"; }
   if ($cmp == 0) {return "="; }
   if ($cmp >  0) {return ">"; }
}

print('35   <=> 36       = ', format_cmp(35   <=> 36      ),  '   ', format_cmp(compare(35,   36      )), ' = compare(35,   36      )',  "\n");
print('35   <=> 35       = ', format_cmp(35   <=> 35      ),  '   ', format_cmp(compare(35,   35      )), ' = compare(35,   35      )',  "\n");
print('36   <=> 35       = ', format_cmp(36   <=> 35      ),  '   ', format_cmp(compare(36,   35      )), ' = compare(36,   35      )',  "\n");
print('36.8 <=> 36.6+0.2 = ', format_cmp(36.8 <=> 36.6+0.2),  '   ', format_cmp(compare(36.8, 36.6+0.2)), ' = compare(36.8, 36.6+0.2)',  "\n");

__END__
output
======
35   <=> 36       = <   < = compare(35,   36      )
35   <=> 35       = =   = = compare(35,   35      )
36   <=> 35       = >   > = compare(36,   35      )
36.8 <=> 36.6+0.2 = <   = = compare(36.8, 36.6+0.2)