Mono.Math.BigInteger.ModulusRing.EvenModTwoPow C# (CSharp) Méthode

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

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

				uint value = exp.data [exp.length - 1];
				uint mask = 0x80000000;

				// Find the first bit of the exponent
				while ((value & mask) == 0)
					mask >>= 1;

				//
				// We know that the first itr will make the val 2,
				// so eat one bit of the exponent
				//
				mask >>= 1;

				uint wPos = exp.length - 1;

				do {
					value = exp.data [wPos];
					do {
						Kernel.SquarePositive (resultNum, ref wkspace);
						if (resultNum.length >= mod.length)
							BarrettReduction (resultNum);

						if ((value & mask) != 0) {
							//
							// 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) {
									uu = u;
									uint c = 0;
									uint [] s = mod.data;
									uint i = 0;
									do {
										uint a = s [i];
										if (((a += c) < c) | ((* (uu++) -= a) > ~a))
											c = 1;
										else
											c = 0;
										i++;
									} while (uu < uuE);
								}
							}
						}
					} while ((mask >>= 1) > 0);
					mask = 0x80000000;
				} while (wPos-- > 0);

				return resultNum;
			}