1. A method of generating an exponent result and a rounded exponent result for an addition operation performed on two numbers in a floating point adder and for generating overflow and underflow flags for the exponent result and the rounded exponent result, wherein each number comprises an exponent and a mantissa, the method comprising the steps of: generating first and second exponent values using the greater exponent of the two numbers, each of the first and second exponent values comprising n bits; providing a binary value which represents a number of bit shifts required to normalise a mantissa result produced by the addition operation, the binary value comprising m bits, where m is less than n; dividing each one of the first and second exponent values into two groups of bits, a first group comprising m of the least significant bits of an exponent value and a second group comprising (n-m) of the most significant bits of the exponent value; decrementing the second group of (n-m) bits of each of the first and second exponent values by one so as to provide a decremented most significant bit result for the each of the first and second exponent values; detecting underflow of the exponent result and rounded exponent result by checking the decremented most significant bit result of the first exponent value and the second group of (n-m) bits of the first exponent value respectively and generating in response to the checking step first and second underflow flags respectively; detecting overflow of the exponent result and rounded exponent result by checking the decremented most significant bit result of the second exponent value and the second group of (n-m) bits of the second exponent value respectively and generating in response to the checking step first and second overflow flags respectively; subtracting the binary value from the first group of m bits of each of the first and second exponent values so as to provide a least significant bit subtraction result and borrow flags for each of the first and second exponent values, the borrow flags indicating whether the subtraction step generates a borrow of one or the subtraction step generates a borrow of zero; selecting for each of the first and second exponent values and in response to the borrow flags, the respective decremented most significant bit result for a borrow of one or the respective second group of (n-m) bits for a borrow of zero so as to provide a selected result for each of the first and second exponent values; combining for each of the exponent values the respective selected result with the respective least significant bit subtraction result so as to generate the exponent result and the rounded exponent result; and providing the exponent result and corresponding first underflow flag and first overflow flag and providing the rounded exponent result and corresponding second underflow flag and second overflow flag at outputs of the floating point adder.