Large Integer Computing - Introduction to Cryptography with Java Applets - page 53

This returns a random number uniformly distributed on the interval [0, 2 numBits 1],

assuming a fair source of random bits is provided in rndSrc. Note that this constructor always
returns a nonnegative BigInteger. It throws an IllegalArgumentException if numBits < 0.

E XAMPLE . This constructor just generates random positive integers without regard to pri-
mality. Again, to ensure randomness which is hard to predict, SecureRandom objects should
be used, as seen here:

SecureRandom sr=new SecureRandom();
BigInteger p=new BigInteger(1024,sr);

2.6

METHODS
This is the last of the constructors; the BigInteger methods follow:

• public static BigInteger valueOf(long val)

Returns a BigInteger with the specified value. This factory is provided in preference to
a (long) constructor because it allows for reuse of frequently used BigIntegers, such as 0 and
1, obviating the need for exported constants.

E XAMPLE .

(Note that this is a static method, and so is called by the class name):

final BigInteger ONE=BigInteger.valueOf(1);

The methods following perform basic arithmetic with BigIntegers.

• public BigInteger add(BigInteger val) throws ArithmeticException

Returns a BigInteger whose value is ( this + val).

• public BigInteger subtract(BigInteger val)

Returns a BigInteger whose value is ( this val).

• public BigInteger multiply(BigInteger val)

Returns a BigInteger whose value is ( this · val).

• public BigInteger divide(BigInteger val) throws ArithmeticException

Returns a BigInteger whose value is the quotient of ( this / val). It throws an ArithmeticEx-
ception if val = 0.

• public BigInteger remainder(BigInteger val) throws
ArithmeticException

Returns a BigInteger whose value is the remainder of ( this / val). It throws an Arith-

meticException if val = 0.