\I'm not exactly sure how useful the code is, but the reference in the pod should be.

#! perl -slw

=pod Extract from [perlnumber]

 On typical hardware, floating point values can store
 numbers with up to 53 binary digits, and with binary  
exponents between -1024 and 1024. In decimal representation 
this is close to 16 decimal digits and decimal exponents in 
the range of -304..304. The upshot of all this is that Perl 
cannot store a number like 12345678901234567 as a floating 
point number on such architectures without loss of 
information.

 =cut
 
use strict;
use Math::BigFloat;

my $num = '1234567890123456789';

my $bf = Math::BigFloat->new();

for my $digits (14.. 17) {
    my $strnum = substr( $num, 0, $digits);
    $bf = Math::BigFloat->new( $strnum );
    my $double = 0+$strnum;
    print $bf, $bf - $double ? 'Use BigFloat': 'Use native';
}
__END__
12345678901234.Use native
123456789012345.Use native
1234567890123456.Use BigFloat
12345678901234567.Use BigFloat
[download]