public void Int128RandomArithmetic()
{
Random rng = new Random(314159);
foreach (Int128 x in GetRandomInt128(8, rng))
{
// Relation of addition to multiplication
Assert.IsTrue(-x == -1 * x);
Assert.IsTrue(0 == 0 * x);
Assert.IsTrue(x == 1 * x);
Assert.IsTrue(x + x == 2 * x);
Assert.IsTrue(x + x + x == 3 * x);
foreach (Int128 y in GetRandomInt128(8, rng))
{
// Subtraction and addition are inverses
Assert.IsTrue(y + (x - y) == x);
// Division methods agree
Int128 q = Int128.DivRem(x, y, out Int128 r);
Assert.IsTrue(q == x / y);
Assert.IsTrue(r == x % y);
// Division and multiplication are inverses
Assert.IsTrue(q * y + r == x);
}
}
}
public void Int128BigIntegerAgreement()
{
Random rng = new Random(3);
foreach (Int128 u in GetRandomInt128(10, rng))
{
BigInteger u1 = BigInteger.Parse(u.ToString());
foreach (Int128 v in GetRandomInt128(10, rng))
{
BigInteger v1 = BigInteger.Parse(v.ToString());
// Comparison
Assert.IsTrue((u < v) == (u1 < v1));
Assert.IsTrue((u > v) == (u1 > v1));
// To discard possible higher order bits in BigInteger results,
// coerce the result into an Int128.
// Sum
Int128 s = u + v;
BigInteger s1 = u1 + v1;
Assert.IsTrue((Int128)s1 == s);
// Difference
Int128 d = u - v;
BigInteger d1 = u1 - v1;
Assert.IsTrue((Int128)d1 == d);
// Product
Int128 p = u * v;
BigInteger p1 = u1 * v1;
Assert.IsTrue((Int128)p1 == p);
// Quotient
// Since results are guaranteed to fit in Int128, we can safely compare to BigInteger directly.
Int128 q = Int128.DivRem(u, v, out Int128 r);
BigInteger q1 = BigInteger.DivRem(u1, v1, out BigInteger r1);
Assert.IsTrue((BigInteger)q == q1);
Assert.IsTrue((BigInteger)r == r1);
}
}
}
