Sample Code

#!/usr/bin/perl
use warnings;
use strict;

use Inline C => <<'END_C';

#include <fenv.h>

int _getround()
{
    return fegetround();
}

int _setround(int mode)
{
    return fesetround(mode);
}

int _round_down()
{
    return fesetround(FE_DOWNWARD);
}

END_C

## simulate my object
my $one   = 1.0;
my $three = 3.0;

## save the rounding mode and set to round towards negative infinity
my $mode = _getround();
my $changed = _round_down();

## perform the calculations
my $lb = $one / $three;
my $ub = -( -$one / $three );

## restore the original rounding mode to be nice
_setround($mode);

## display the results
printf( "\$lb = %.23f\n", $lb );
printf( "\$ub = %.23f\n", $ub );
print "\$lb == \$ub ", $lb == $ub ? 'true' : 'false', "\n";
print "\$changed = $changed\n";
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Sample Output

P:\>fround
$mode = 0
$lb = 0.33333333333333331000000
$ub = 0.33333333333333337000000
$lb == $ub false
$changed = 0
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