How to add two numbers in IEE754 half precision format?
The second number has zero as exponent and has non zero mantissa, so it is a Denormal (aka Subnormals)

0 01111 1100001111 = 1.1100001111 * 2**0   = 1.1100001111
0 01110 1100001111 = 1.1100001111 * 2**-1  = 0.11100001111
0 01101 1100001111 = 1.1100001111 * 2**-2  = 0.011100001111
0 01100 1100001111 = 1.1100001111 * 2**-3  = 0.0011100001111
0 01011 1100001111 = 1.1100001111 * 2**-4  = 0.00011100001111
0 01010 1100001111 = 1.1100001111 * 2**-5  = 0.000011100001111
0 01001 1100001111 = 1.1100001111 * 2**-6  = 0.0000011100001111
0 01000 1100001111 = 1.1100001111 * 2**-7  = 0.00000011100001111
0 00111 1100001111 = 1.1100001111 * 2**-8  = 0.000000011100001111
0 00110 1100001111 = 1.1100001111 * 2**-9  = 0.0000000011100001111
0 00101 1100001111 = 1.1100001111 * 2**-10 = 0.00000000011100001111
0 00100 1100001111 = 1.1100001111 * 2**-11 = 0.000000000011100001111
0 00011 1100001111 = 1.1100001111 * 2**-12 = 0.0000000000011100001111
0 00010 1100001111 = 1.1100001111 * 2**-13 = 0.00000000000011100001111
0 00001 1100001111 = 1.1100001111 * 2**-14 = 0.000000000000011100001111
0 00000 1100001111 = 0.1100001111 * 2**-14 = 0.000000000000001100001111


Denormals have no leading 1 and use the same exponent as smallest normal numbers.

To perform an addition, you need to align mantissas, then perform an addition or a subtraction (if the signs are opposite, as this is the case here.) :

  -1000000001.0
  +         0.000000000000001100001111
 =-1000000000.111111111111110011110001


Here the difference between the two numbers is too large and the small number will disappear after rounding, except if you use a special rounding mode (as round towards zero or towards +infinite)

Maybe you have other sample additions that are more interesting.



Using two's complement, one can make subtractions out of additions :

    -         0.000000000000001100001111
 ! = 1111111111.111111111111110011110000 : Invert all digits
+1 = 1111111111.111111111111110011110001 : plus one.


The addition-that-is-a-subtraction becomes :

     1000000001.000000000000000000000000
   + 1111111111.111111111111110011110001
= [1]1000000000.111111111111110011110001