1. An apparatus for generating a sum of floating-point input values, the apparatus comprising: storage circuitry to store multiple partial sum floating-point values; selection circuitry to select a partial sum floating-point value of the multiple partial sum floating-point values in dependence on a least significant portion of a first exponent value for a floating-point input value; comparison circuitry to compare the first exponent value with a second exponent value stored for the selected partial sum floating-point value; and accumulation circuitry to perform an addition procedure, wherein the addition procedure comprises: replacing a mantissa value of the selected partial sum floating-point value with a mantissa sum of the floating-point input value and the selected partial sum floating-point value, when the first exponent value and the second exponent value are equal; and replacing the selected partial sum floating-point value with the floating-point input value in the selected partial sum floating-point value, when the first exponent value is larger than the second exponent value.