For an Inline::C solution, the following works ok for me with gcc on Windows: 
use strict;
use warnings;

use Inline C => Config =>
 BUILD_NOISY => 1,
 ;

use Inline C => <<'EOC';

double nxtafter(double in, double dir) {
  return nextafter(in, dir);
}

EOC

my $pos_inf = (99 ** 99) ** 99;
my $neg_inf = -$pos_inf;

my $next_down = nxtafter(1.9041105342991877e+258, $neg_inf);

printf "%.16e\n", $next_down;

my $next_up = nxtafter(-8.2727285363069939e-293, $pos_inf);

printf "%.16e\n", $next_up;

__END__
Outputs:
1.9041105342991875e+258
-8.2727285363069927e-293

[download]
With the latest MS compiler that I have (14.00.40310.41) I need to replace "nextafter" with "_nextafter" in order to get the script to compile.
But it then produces incorrect results anyway: 
1.9041105342991884e+258
-7.9999999999999937e-293

[download]
Perhaps a more recent MS compiler fares better.

Cheers,
Rob

In reply to Re: Determining the minimum representable increment/decrement possible? by syphilis
in thread Determining the minimum representable increment/decrement possible? by BrowserUk

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