f  A single-precision float in native format.
d  A double-precision float in native format.

F  A Perl internal floating-point value (NV) in native format
D  A float of long-double precision in native format.
     (Long doubles are available only if your system supports
      long double values. Raises an exception otherwise.              (* WRONG see demo)
      Note that there are different long double formats.)

##</code><code>##

main::(-e:1):	0
  DB<1> say unpack "B*", pack "f", 1/3
10101011101010101010101000111110

  DB<2> say unpack "B*", pack "d", 1/3
0101010101010101010101010101010101010101010101011101010100111111

  DB<3> say unpack "B*", pack "F", 1/3
0101010101010101010101010101010101010101010101011101010100111111

  DB<4> say unpack "B*", pack "D", 1/3
00000000101010001010101010101010101010101010101010101010101010101111110100111111000000000000000000000000000000000000000000000000

  DB<5> use warnings; say unpack "B*", pack "D", 1/3         # NO EXCEPTION RAISED
00000000101010001010101010101010101010101010101010101010101010101111110100111111000000000000000000000000000000000000000000000000