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for my $a (-2..10, 0.2, -0.2, 1 + 0.25e-15) {  
        $_ = unpack("b*", pack("d", $a));   # double to bit-pattern 
...
        s/^(..)(.{12})(.*)/Sgn:$1  Exp: $2  Mant:(1,)$3/; 
        print "$a\t -- $_\n";
}

my $a = 1+0.25e-15;# hidden bit and last bit of mantissa: 1
print "Test                : is int.?   correct?\n";
...
abs(a-int(a) < 1e-15: yes        no!
abs(a-int(a) > 0    : no         yes
epsilon < 2.22045e-16 required (here!)