For example, represent the value -0.5 as a twos complement floating point number with an eight bit mantissa and a four bit exponent.
The twos complement of -0.5 is 1.1.
To make this into a normalised floating point number we need to carry out a single binary left shift.
Mantissa: 0.1000000
Exponent: 1111
This gives an exponent value of -1 and a mantissa value of 0.5.
-1 x 2-1 = -0.5