C# BigInteger.TestBit方法代码示例

			private unsafe BigInteger OddModTwoPow (BigInteger exp)
			{

				uint [] wkspace = new uint [mod.length << 1 + 1];

				BigInteger resultNum = Montgomery.ToMont ((BigInteger)2, this.mod);
				resultNum = new BigInteger (resultNum, mod.length << 1 +1);

				uint mPrime = Montgomery.Inverse (mod.data [0]);

				//
				// TODO: eat small bits, the ones we can do with no modular reduction
				//
				uint pos = (uint)exp.BitCount () - 2;

				do {
					Kernel.SquarePositive (resultNum, ref wkspace);
					resultNum = Montgomery.Reduce (resultNum, mod, mPrime);

					if (exp.TestBit (pos)) {
						//
						// resultNum = (resultNum * 2) % mod
						//

						fixed (uint* u = resultNum.data) {
							//
							// Double
							//
							uint* uu = u;
							uint* uuE = u + resultNum.length;
							uint x, carry = 0;
							while (uu < uuE) {
								x = *uu;
								*uu = (x << 1) | carry;
								carry = x >> (32 - 1);
								uu++;
							}

							// subtraction inlined because we know it is square
							if (carry != 0 || resultNum >= mod) {
								fixed (uint* s = mod.data) {
									uu = u;
									uint c = 0;
									uint* ss = s;
									do {
										uint a = *ss++;
										if (((a += c) < c) | ((* (uu++) -= a) > ~a))
											c = 1;
										else
											c = 0;
									} while (uu < uuE);
								}
							}
						}
					}
				} while (pos-- > 0);

				resultNum = Montgomery.Reduce (resultNum, mod, mPrime);
				return resultNum;
			}

			private unsafe BigInteger EvenPow (uint b, BigInteger exp)
			{
				exp.Normalize ();
				uint [] wkspace = new uint [mod.length << 1 + 1];
				BigInteger resultNum = new BigInteger ((BigInteger)b, mod.length << 1 + 1);

				uint pos = (uint)exp.BitCount () - 2;

				//
				// We know that the first itr will make the val b
				//

				do {
					//
					// r = r ^ 2 % m
					//
					Kernel.SquarePositive (resultNum, ref wkspace);
					if (!(resultNum.length < mod.length))
						BarrettReduction (resultNum);

					if (exp.TestBit (pos)) {

						//
						// r = r * b % m
						//

						// TODO: Is Unsafe really speeding things up?
						fixed (uint* u = resultNum.data) {

							uint i = 0;
							ulong mc = 0;

							do {
								mc += (ulong)u [i] * (ulong)b;
								u [i] = (uint)mc;
								mc >>= 32;
							} while (++i < resultNum.length);

							if (resultNum.length < mod.length) {
								if (mc != 0) {
									u [i] = (uint)mc;
									resultNum.length++;
									while (resultNum >= mod)
										Kernel.MinusEq (resultNum, mod);
								}
							} else if (mc != 0) {

								//
								// First, we estimate the quotient by dividing
								// the first part of each of the numbers. Then
								// we correct this, if necessary, with a subtraction.
								//

								uint cc = (uint)mc;

								// We would rather have this estimate overshoot,
								// so we add one to the divisor
								uint divEstimate = (uint) ((((ulong)cc << 32) | (ulong) u [i -1]) /
									(mod.data [mod.length-1] + 1));

								uint t;

								i = 0;
								mc = 0;
								do {
									mc += (ulong)mod.data [i] * (ulong)divEstimate;
									t = u [i];
									u [i] -= (uint)mc;
									mc >>= 32;
									if (u [i] > t) mc++;
									i++;
								} while (i < resultNum.length);
								cc -= (uint)mc;

								if (cc != 0) {

									uint sc = 0, j = 0;
									uint [] s = mod.data;
									do {
										uint a = s [j];
										if (((a += sc) < sc) | ((u [j] -= a) > ~a)) sc = 1;
										else sc = 0;
										j++;
									} while (j < resultNum.length);
									cc -= sc;
								}
								while (resultNum >= mod)
									Kernel.MinusEq (resultNum, mod);
							} else {
								while (resultNum >= mod)
									Kernel.MinusEq (resultNum, mod);
							}
						}
					}
				} while (pos-- > 0);

				return resultNum;
			}

			private BigInteger OddPow (BigInteger b, BigInteger exp)
			{
				BigInteger resultNum = new BigInteger (Montgomery.ToMont (1, mod), mod.length << 1);
				BigInteger tempNum = new BigInteger (Montgomery.ToMont (b, mod), mod.length << 1);  // ensures (tempNum * tempNum) < b^ (2k)
				uint mPrime = Montgomery.Inverse (mod.data [0]);
				uint totalBits = (uint)exp.BitCount ();

				uint [] wkspace = new uint [mod.length << 1];

				// perform squaring and multiply exponentiation
				for (uint pos = 0; pos < totalBits; pos++) {
					if (exp.TestBit (pos)) {

						Array.Clear (wkspace, 0, wkspace.Length);
						Kernel.Multiply (resultNum.data, 0, resultNum.length, tempNum.data, 0, tempNum.length, wkspace, 0);
						resultNum.length += tempNum.length;
						uint [] t = wkspace;
						wkspace = resultNum.data;
						resultNum.data = t;

						Montgomery.Reduce (resultNum, mod, mPrime);
					}

					// the value of tempNum is required in the last loop
					if (pos < totalBits - 1) {
						Kernel.SquarePositive (tempNum, ref wkspace);
						Montgomery.Reduce (tempNum, mod, mPrime);
					}
				}

				Montgomery.Reduce (resultNum, mod, mPrime);
				return resultNum;
			}

			public BigInteger Pow (BigInteger a, BigInteger k)
			{
				BigInteger b = new BigInteger (1);
				if (k == 0)
					return b;

				BigInteger A = a;
				if (k.TestBit (0))
					b = a;

				for (int i = 1; i < k.BitCount (); i++) {
					A = Multiply (A, A);
					if (k.TestBit (i))
						b = Multiply (A, b);
				}
				return b;
			}