perl -le 'print sprintf("%6.1f: ", $_),
                reverse(split //, 
                  unpack("b*", pack("F", $_))) 
          for map {eval} @ARGV' 

##</code><code>##

33.3 33.4 '33.3+33.3' '33.4+33.3' '33.3+33.3+33.4' '33.4+33.3+33.3'

##</code><code>##

 33.3:0100000001000000101001100110011001100110011001100110011001100110
 33.4:0100000001000000101100110011001100110011001100110011001100110011
 66.6:0100000001010000101001100110011001100110011001100110011001100110
 66.7:0100000001010000101011001100110011001100110011001100110011001100
100.0:0100000001011001000000000000000000000000000000000000000000000000
100.0:0100000001011000111111111111111111111111111111111111111111111111

##</code><code>##

33.3 is represented as 2^5 times
  B1.0000101001100110011001100110011001100110011001100110
33.4 is represented as 2^5 times
  B1.0000101100110011001100110011001100110011001100110011
66.6 is represented as 2^6 times
  B1.0000101001100110011001100110011001100110011001100110
66.7 is represented as 2^6 times
  B1.0000101011001100110011001100110011001100110011001100
100.0 (exactly) is represented as 2^6 times
  B1.1001000000000000000000000000000000000000000000000000
100.0 (not quite) is represented as 2^6 times
  B1.1000111111111111111111111111111111111111111111111111

##</code><code>##

33.3 + 33.3 is then 2^5 times:
   1.0000101001100110011001100110011001100110011001100110
+  1.0000101001100110011001100110011001100110011001100110
---------------------------------------------------------
  10.0001010011001100110011001100110011001100110011001100

But that's too long for a double, so it's represented
as 2^6 times
   1.0000101001100110011001100110011001100110011001100110


33.4 + 33.3 is then 2^5 times:
   1.0000101100110011001100110011001100110011001100110011
+  1.0000101001100110011001100110011001100110011001100110
---------------------------------------------------------
  10.0001010110011001100110011001100110011001100110011001

Now, smashing that into a double results in 2^6 times:
   1.0000101011001100110011001100110011001100110011001100

##</code><code>##

66.6 + 33.4 is now 2^6 times:
   1.0000101001100110011001100110011001100110011001100110
+  0.1000010110011001100110011001100110011001100110011010
---------------------------------------------------------
   1.1001000000000000000000000000000000000000000000000000

66.7 + 33.3 is now 2^6 times:
   1.0000101011001100110011001100110011001100110011001100
+  0.1000010100110011001100110011001100110011001100110011
---------------------------------------------------------
   1.1000111111111111111111111111111111111111111111111111