using System;
using Org.BouncyCastle.Crypto.Utilities;
using Org.BouncyCastle.Security;

namespace Org.BouncyCastle.Math.Raw;

internal abstract class Mod
{
	private static readonly SecureRandom RandomSource = new SecureRandom();

	public static void Invert(uint[] p, uint[] x, uint[] z)
	{
		int num = p.Length;
		if (Nat.IsZero(num, x))
		{
			throw new ArgumentException("cannot be 0", "x");
		}
		if (Nat.IsOne(num, x))
		{
			Array.Copy(x, 0, z, 0, num);
			return;
		}
		uint[] array = Nat.Copy(num, x);
		uint[] array2 = Nat.Create(num);
		array2[0] = 1u;
		int xc = 0;
		if ((array[0] & 1) == 0)
		{
			InversionStep(p, array, num, array2, ref xc);
		}
		if (Nat.IsOne(num, array))
		{
			InversionResult(p, xc, array2, z);
			return;
		}
		uint[] array3 = Nat.Copy(num, p);
		uint[] array4 = Nat.Create(num);
		int xc2 = 0;
		int num2 = num;
		while (true)
		{
			if (array[num2 - 1] == 0 && array3[num2 - 1] == 0)
			{
				num2--;
			}
			else if (Nat.Gte(num, array, array3))
			{
				Nat.SubFrom(num, array3, array);
				xc += Nat.SubFrom(num, array4, array2) - xc2;
				InversionStep(p, array, num2, array2, ref xc);
				if (Nat.IsOne(num, array))
				{
					InversionResult(p, xc, array2, z);
					return;
				}
			}
			else
			{
				Nat.SubFrom(num, array, array3);
				xc2 += Nat.SubFrom(num, array2, array4) - xc;
				InversionStep(p, array3, num2, array4, ref xc2);
				if (Nat.IsOne(num, array3))
				{
					break;
				}
			}
		}
		InversionResult(p, xc2, array4, z);
	}

	public static uint[] Random(uint[] p)
	{
		int num = p.Length;
		uint[] array = Nat.Create(num);
		uint num2 = p[num - 1];
		num2 |= num2 >> 1;
		num2 |= num2 >> 2;
		num2 |= num2 >> 4;
		num2 |= num2 >> 8;
		num2 |= num2 >> 16;
		do
		{
			byte[] array2 = new byte[num << 2];
			RandomSource.NextBytes(array2);
			Pack.BE_To_UInt32(array2, 0, array);
			uint[] array4;
			uint[] array3 = (array4 = array);
			int num3 = num - 1;
			nint num4 = num3;
			array3[num3] = array4[num4] & num2;
		}
		while (Nat.Gte(num, array, p));
		return array;
	}

	public static void Add(uint[] p, uint[] x, uint[] y, uint[] z)
	{
		int len = p.Length;
		if (Nat.Add(len, x, y, z) != 0)
		{
			Nat.SubFrom(len, p, z);
		}
	}

	public static void Subtract(uint[] p, uint[] x, uint[] y, uint[] z)
	{
		int len = p.Length;
		if (Nat.Sub(len, x, y, z) != 0)
		{
			Nat.AddTo(len, p, z);
		}
	}

	private static void InversionResult(uint[] p, int ac, uint[] a, uint[] z)
	{
		if (ac < 0)
		{
			Nat.Add(p.Length, a, p, z);
		}
		else
		{
			Array.Copy(a, 0, z, 0, p.Length);
		}
	}

	private static void InversionStep(uint[] p, uint[] u, int uLen, uint[] x, ref int xc)
	{
		int len = p.Length;
		int num = 0;
		while (u[0] == 0)
		{
			Nat.ShiftDownWord(uLen, u, 0u);
			num += 32;
		}
		int trailingZeroes = GetTrailingZeroes(u[0]);
		if (trailingZeroes > 0)
		{
			Nat.ShiftDownBits(uLen, u, trailingZeroes, 0u);
			num += trailingZeroes;
		}
		for (int i = 0; i < num; i++)
		{
			if ((x[0] & 1) != 0)
			{
				if (xc < 0)
				{
					xc += (int)Nat.AddTo(len, p, x);
				}
				else
				{
					xc += Nat.SubFrom(len, p, x);
				}
			}
			Nat.ShiftDownBit(len, x, (uint)xc);
		}
	}

	private static int GetTrailingZeroes(uint x)
	{
		int num = 0;
		while ((x & 1) == 0)
		{
			x >>= 1;
			num++;
		}
		return num;
	}
}