internal static BigInteger evenModPow(BigInteger _base, BigInteger exponent,
BigInteger modulus)
{
// PRE: (base > 0), (exponent > 0), (modulus > 0) and (modulus even)
// STEP 1: Obtain the factorization 'modulus'= q * 2^j.
int j = modulus.getLowestSetBit();
BigInteger q = modulus.shiftRight(j);
// STEP 2: Compute x1 := base^exponent (mod q).
BigInteger x1 = oddModPow(_base, exponent, q);
// STEP 3: Compute x2 := base^exponent (mod 2^j).
BigInteger x2 = pow2ModPow(_base, exponent, j);
// STEP 4: Compute q^(-1) (mod 2^j) and y := (x2-x1) * q^(-1) (mod 2^j)
BigInteger qInv = modPow2Inverse(q, j);
BigInteger y = (x2.subtract(x1)).multiply(qInv);
inplaceModPow2(y, j);
if (y.sign < 0)
{
y = y.add(BigInteger.getPowerOfTwo(j));
}
// STEP 5: Compute and return: x1 + q * y
return(x1.add(q.multiply(y)));
}
private static bool millerRabin(BigInteger n, int t)
{
// PRE: n >= 0, t >= 0
BigInteger x; // x := UNIFORM{2...n-1}
BigInteger y; // y := x^(q * 2^j) mod n
BigInteger n_minus_1 = n.subtract(BigInteger.ONE); // n-1
int bitLength = n_minus_1.bitLength(); // ~ log2(n-1)
// (q,k) such that: n-1 = q * 2^k and q is odd
int k = n_minus_1.getLowestSetBit();
BigInteger q = n_minus_1.shiftRight(k);
Random rnd = new Random();
for (int i = 0; i < t; i++)
{
// To generate a witness 'x', first it use the primes of table
if (i < primes.Length)
{
x = BIprimes[i];
}
else /*
* It generates random witness only if it's necesssary. Note
* that all methods would call Miller-Rabin with t <= 50 so
* this part is only to do more robust the algorithm
*/
{
do
{
x = new BigInteger(bitLength, rnd);
} while ((x.compareTo(n) >= BigInteger.EQUALS) || (x.sign == 0) ||
x.isOne());
}
y = x.modPow(q, n);
if (y.isOne() || y.Equals(n_minus_1))
{
continue;
}
for (int j = 1; j < k; j++)
{
if (y.Equals(n_minus_1))
{
continue;
}
y = y.multiply(y).mod(n);
if (y.isOne())
{
return(false);
}
}
if (!y.Equals(n_minus_1))
{
return(false);
}
}
return(true);
}
private static int howManyIterations(BigInteger bi, int n)
{
int i = n - 1;
if (bi.sign > 0)
{
while (!bi.testBit(i))
{
i--;
}
return(n - 1 - i);
}
else
{
while (bi.testBit(i))
{
i--;
}
return(n - 1 - Math.Max(i, bi.getLowestSetBit()));
}
}
private static int howManyIterations(BigInteger bi, int n)
{
int i = n - 1;
if (bi.sign > 0) {
while (!bi.testBit(i))
i--;
return n - 1 - i;
} else {
while (bi.testBit(i))
i--;
return n - 1 - Math.Max(i, bi.getLowestSetBit());
}
}
internal static BigInteger gcdBinary(BigInteger op1, BigInteger op2)
{
// PRE: (op1 > 0) and (op2 > 0)
/*
* Divide both number the maximal possible times by 2 without rounding
* gcd(2*a, 2*b) = 2 * gcd(a,b)
*/
int lsb1 = op1.getLowestSetBit();
int lsb2 = op2.getLowestSetBit();
int pow2Count = Math.Min(lsb1, lsb2);
BitLevel.inplaceShiftRight(op1, lsb1);
BitLevel.inplaceShiftRight(op2, lsb2);
BigInteger swap;
// I want op2 > op1
if (op1.compareTo(op2) == BigInteger.GREATER) {
swap = op1;
op1 = op2;
op2 = swap;
}
do { // INV: op2 >= op1 && both are odd unless op1 = 0
// Optimization for small operands
// (op2.bitLength() < 64) implies by INV (op1.bitLength() < 64)
if (( op2.numberLength == 1 )
|| ( ( op2.numberLength == 2 ) && ( op2.digits[1] > 0 ) )) {
op2 = BigInteger.valueOf(Division.gcdBinary(op1.longValue(),
op2.longValue()));
break;
}
// Implements one step of the Euclidean algorithm
// To reduce one operand if it's much smaller than the other one
if (op2.numberLength > op1.numberLength * 1.2) {
op2 = op2.remainder(op1);
if (op2.signum() != 0) {
BitLevel.inplaceShiftRight(op2, op2.getLowestSetBit());
}
} else {
// Use Knuth's algorithm of successive subtract and shifting
do {
Elementary.inplaceSubtract(op2, op1); // both are odd
BitLevel.inplaceShiftRight(op2, op2.getLowestSetBit()); // op2 is even
} while (op2.compareTo(op1) >= BigInteger.EQUALS);
}
// now op1 >= op2
swap = op2;
op2 = op1;
op1 = swap;
} while (op1.sign != 0);
return op2.shiftLeft(pow2Count);
}
internal static BigInteger evenModPow(BigInteger _base, BigInteger exponent,
BigInteger modulus)
{
// PRE: (base > 0), (exponent > 0), (modulus > 0) and (modulus even)
// STEP 1: Obtain the factorization 'modulus'= q * 2^j.
int j = modulus.getLowestSetBit();
BigInteger q = modulus.shiftRight(j);
// STEP 2: Compute x1 := base^exponent (mod q).
BigInteger x1 = oddModPow(_base, exponent, q);
// STEP 3: Compute x2 := base^exponent (mod 2^j).
BigInteger x2 = pow2ModPow(_base, exponent, j);
// STEP 4: Compute q^(-1) (mod 2^j) and y := (x2-x1) * q^(-1) (mod 2^j)
BigInteger qInv = modPow2Inverse(q, j);
BigInteger y = (x2.subtract(x1)).multiply(qInv);
inplaceModPow2(y, j);
if (y.sign < 0) {
y = y.add(BigInteger.getPowerOfTwo(j));
}
// STEP 5: Compute and return: x1 + q * y
return x1.add(q.multiply(y));
}
internal static BigInteger gcdBinary(BigInteger op1, BigInteger op2)
{
// PRE: (op1 > 0) and (op2 > 0)
/*
* Divide both number the maximal possible times by 2 without rounding
* gcd(2*a, 2*b) = 2 * gcd(a,b)
*/
int lsb1 = op1.getLowestSetBit();
int lsb2 = op2.getLowestSetBit();
int pow2Count = Math.Min(lsb1, lsb2);
BitLevel.inplaceShiftRight(op1, lsb1);
BitLevel.inplaceShiftRight(op2, lsb2);
BigInteger swap;
// I want op2 > op1
if (op1.compareTo(op2) == BigInteger.GREATER)
{
swap = op1;
op1 = op2;
op2 = swap;
}
do // INV: op2 >= op1 && both are odd unless op1 = 0
// Optimization for small operands
// (op2.bitLength() < 64) implies by INV (op1.bitLength() < 64)
{
if ((op2.numberLength == 1) ||
((op2.numberLength == 2) && (op2.digits[1] > 0)))
{
op2 = BigInteger.valueOf(Division.gcdBinary(op1.longValue(),
op2.longValue()));
break;
}
// Implements one step of the Euclidean algorithm
// To reduce one operand if it's much smaller than the other one
if (op2.numberLength > op1.numberLength * 1.2)
{
op2 = op2.remainder(op1);
if (op2.signum() != 0)
{
BitLevel.inplaceShiftRight(op2, op2.getLowestSetBit());
}
}
else
{
// Use Knuth's algorithm of successive subtract and shifting
do
{
Elementary.inplaceSubtract(op2, op1); // both are odd
BitLevel.inplaceShiftRight(op2, op2.getLowestSetBit()); // op2 is even
} while (op2.compareTo(op1) >= BigInteger.EQUALS);
}
// now op1 >= op2
swap = op2;
op2 = op1;
op1 = swap;
} while (op1.sign != 0);
return(op2.shiftLeft(pow2Count));
}
