A class used to represent multiprecision integers that makes efficient use of allocated space by allowing a number to occupy only part of an array so that the arrays do not have to be reallocated as often. When performing an operation with many iterations the array used to hold a number is only increased when necessary and does not have to be the same size as the number it represents. A mutable number allows calculations to occur on the same number without having to create a new number for every step of the calculation as occurs with BigIntegers. Note that SignedMutableBigIntegers only support signed addition and subtraction. All other operations occur as with MutableBigIntegers.