I was studying this thread offline, and found this old snippet in my "snippet library". It runs until it "hits the wall" and yields close to the DBL_MAX and DBL_MIN values. Wriitten by some unknown monk. FWIW

#!/usr/bin/perl
# get the largest and smallest float usable without 
# Math::BigFloat 
my $i = 1.0;
my $lasti;
my $bignum;
for ( ; ; ) {
    $bignum = $lasti;
    $lasti  = $i;
    $i *= 2;

    #print $i,"\n"; 
    last if ( $i == $lasti );
}
print "$bignum\n";

#The last number before "inf" is your largest representable 
#float (8.98846567431158e+307 on my system). 

#A similar trick with division by 2 will give you the smallest 
#representable float (4.94065645841247e-324 on my system). 

$i = 1.0;
$lasti;
my $smallnum;
for ( ; ; ) {
    $smallnum = $lasti;
    $lasti    = $i;
    $i /= 2;

    #print $i,"\n"; 
    last if ( $i == $lasti );
}
print "$smallnum\n";
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