public void MmodInverseBigInteger()
{
BigInteger a = zero, mod, inv;
for (int j = 3; j < 50; j++)
{
mod = BigInteger.FromInt64(j);
for (int i = -j + 1; i < j; i++)
{
try {
a = BigInteger.FromInt64(i);
inv = BigMath.ModInverse(a, mod);
Assert.True(one.Equals(((a * inv) % mod)), "bad inverse: " + a + " inv mod " + mod + " equals " + inv);
Assert.True(inv.CompareTo(mod) < 0, "inverse greater than modulo: " + a + " inv mod " + mod + " equals " + inv);
Assert.True(inv.CompareTo(BigInteger.Zero) >= 0, "inverse less than zero: " + a + " inv mod " + mod + " equals " + inv);
} catch (ArithmeticException) {
Assert.True(!one.Equals(BigMath.Gcd(a, mod)), "should have found inverse for " + a + " mod " + mod);
}
}
}
for (int j = 1; j < 10; j++)
{
mod = bi2 + BigInteger.FromInt64(j);
for (int i = 0; i < 20; i++)
{
try {
a = bi3 + (BigInteger.FromInt64(i));
inv = BigMath.ModInverse(a, mod);
Assert.True(one.Equals((a * inv) % mod), "bad inverse: " + a + " inv mod " + mod + " equals " + inv);
Assert.True(inv.CompareTo(mod) < 0, "inverse greater than modulo: " + a + " inv mod " + mod + " equals " + inv);
Assert.True(inv.CompareTo(BigInteger.Zero) >= 0, "inverse less than zero: " + a + " inv mod " + mod + " equals " + inv);
} catch (ArithmeticException) {
Assert.True(!one.Equals(BigMath.Gcd(a, mod)), "should have found inverse for " + a + " mod " + mod);
}
}
}
}
public static BigDecimal Divide(BigDecimal dividend, BigDecimal divisor)
{
BigInteger p = dividend.UnscaledValue;
BigInteger q = divisor.UnscaledValue;
BigInteger gcd; // greatest common divisor between 'p' and 'q'
BigInteger quotient;
BigInteger remainder;
long diffScale = (long)dividend.Scale - divisor.Scale;
int newScale; // the new scale for final quotient
int k; // number of factors "2" in 'q'
int l = 0; // number of factors "5" in 'q'
int i = 1;
int lastPow = BigDecimal.FivePow.Length - 1;
if (divisor.IsZero)
{
// math.04=Division by zero
throw new ArithmeticException(Messages.math04); //$NON-NLS-1$
}
if (p.Sign == 0)
{
return(BigDecimal.GetZeroScaledBy(diffScale));
}
// To divide both by the GCD
gcd = BigMath.Gcd(p, q);
p = p / gcd;
q = q / gcd;
// To simplify all "2" factors of q, dividing by 2^k
k = q.LowestSetBit;
q = q >> k;
// To simplify all "5" factors of q, dividing by 5^l
do
{
quotient = BigMath.DivideAndRemainder(q, BigDecimal.FivePow[i], out remainder);
if (remainder.Sign == 0)
{
l += i;
if (i < lastPow)
{
i++;
}
q = quotient;
}
else
{
if (i == 1)
{
break;
}
i = 1;
}
} while (true);
// If abs(q) != 1 then the quotient is periodic
if (!BigMath.Abs(q).Equals(BigInteger.One))
{
// math.05=Non-terminating decimal expansion; no exact representable decimal result.
throw new ArithmeticException(Messages.math05); //$NON-NLS-1$
}
// The sign of the is fixed and the quotient will be saved in 'p'
if (q.Sign < 0)
{
p = -p;
}
// Checking if the new scale is out of range
newScale = BigDecimal.ToIntScale(diffScale + System.Math.Max(k, l));
// k >= 0 and l >= 0 implies that k - l is in the 32-bit range
i = k - l;
p = (i > 0)
? Multiplication.MultiplyByFivePow(p, i)
: p << -i;
return(new BigDecimal(p, newScale));
}
