A Fast Random Number Generator Based on BigInteger

RandomX.cs

using System;
using System.Numerics;
using System.Security.Cryptography;
public struct RandomX
{
    private readonly RNGCryptoServiceProvider _crng;
    private          int                      _maxByteWidth;
    private          int                      _bitWidth;
    public RandomX(int bitWidth)
    {
        MaxValue      = BigIntegerHelper.GetMaxValueBitWidth(bitWidth);
        _maxByteWidth = bitWidth >> 3;
        OddsOnly      = false;
        Unsigned      = false;
        _crng         = new RNGCryptoServiceProvider();
        _bitWidth     = bitWidth;
    }
    public bool OddsOnly;
    public bool Unsigned;
    public int BitWidth
    {
        get => _bitWidth;
        set
        {
            _bitWidth     = value;
            MaxValue      = BigIntegerHelper.GetMaxValueBitWidth(_bitWidth);
            _maxByteWidth = _bitWidth >> 3;
        }
    }
    public BigInteger MaxValue;
    public bool NextBool()
    {
        return Sample() < .5;
    }
    public char NextChar(char maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (char) (Sample() * maxValue);
    }
    public char NextChar(char minValue, char maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (char) Next(minValue, maxValue);
    }
    public sbyte NextInt8()
    {
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 8)
            BitWidth = 8;
        return (sbyte) Internal();
    }
    public sbyte NextInt8(sbyte maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 8)
            BitWidth = 8;
        return (sbyte) (Sample() * maxValue);
    }
    public sbyte NextInt8(sbyte minValue, sbyte maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 8)
            BitWidth = 8;
        return (sbyte) Next(minValue, maxValue);
    }
    public byte NextUInt8()
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 8)
            BitWidth = 8;
        var n = Internal();
        return (byte) n;
    }
    public byte NextUInt8(byte maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 8)
            BitWidth = 8;
        return (byte) (Sample() * maxValue);
    }
    public byte NextUInt8(byte minValue, byte maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 8)
            BitWidth = 8;
        return (byte) Next(minValue, maxValue);
    }
    public short NextInt16()
    {
        if (_bitWidth < 16)
            BitWidth = 16;
        if (Unsigned)
            Unsigned = false;
        return (short) Internal();
    }
    public short NextInt16(short maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (short) (Sample() * maxValue);
    }
    public short NextInt16(short minValue, short maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (short) Next(minValue, maxValue);
    }
    public ushort NextUInt16()
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (ushort) Internal();
    }
    public ushort NextUInt16(ushort maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (ushort) (Sample() * maxValue);
    }
    public ushort NextUInt16(ushort minValue, ushort maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 16)
            BitWidth = 16;
        return (ushort) Next(minValue, maxValue);
    }
    public int NextInt24()
    {
        BitWidth = 24;
        if (Unsigned)
            Unsigned = false;
        return (int) Internal();
    }
    public int NextInt24(int maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 24;
        return (int) (Sample() * maxValue);
    }
    public int NextInt24(int minValue, int maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 24;
        return (int) Next(minValue, maxValue);
    }
    public uint NextUInt24()
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 24;
        return (uint) Internal();
    }
    public uint NextUInt24(uint maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 24;
        return (uint) (Sample() * maxValue);
    }
    public uint NextUInt24(uint minValue, uint maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 24;
        return (uint) Next(minValue, maxValue);
    }
    public uint NextUInt32()
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 32)
            BitWidth = 32;
        return (uint) Internal();
    }
    public uint NextUInt32(uint maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 32)
            BitWidth = 32;
        return (uint) (Sample() * maxValue);
    }
    public uint NextUInt32(uint minValue, uint maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 32)
            BitWidth = 32;
        return (uint) Next(minValue, maxValue);
    }
    public int NextInt32()
    {
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 32)
            BitWidth = 32;
        return (int) Internal();
    }
    public int NextInt32(int maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 32)
            BitWidth = 32;
        return (int) (Sample() * maxValue);
    }
    public int NextInt32(int minValue, int maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 32)
            BitWidth = 32;
        return (int) Next(minValue, maxValue);
    }
    public long NextUInt40()
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 40;
        return (long) Internal();
    }
    public long NextUInt40(long maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 40;
        return (long) (Sample() * maxValue);
    }
    public long NextUInt40(long minValue, long maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 40;
        return (long) Next(minValue, maxValue);
    }
    public long NextInt40()
    {
        if (Unsigned)
            Unsigned = false;
        BitWidth = 40;
        return (long) Internal();
    }
    public long NextInt40(long maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 40;
        return (long) (Sample() * maxValue);
    }
    public long NextInt40(long minValue, long maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 40;
        return (long) Next(minValue, maxValue);
    }
    public ulong NextUInt48()
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 48;
        return (ulong) Internal();
    }
    public ulong NextUInt48(ulong maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 48;
        return (ulong) (Sample() * maxValue);
    }
    public ulong NextUInt48(ulong minValue, ulong maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 48;
        return (ulong) Next(minValue, maxValue);
    }
    public long NextInt48()
    {
        if (Unsigned)
            Unsigned = false;
        BitWidth = 48;
        return (long) Internal();
    }
    public long NextInt48(long maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 48;
        return (long) (Sample() * maxValue);
    }
    public ulong NextUInt56()
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 56;
        return (ulong) Internal();
    }
    public ulong NextUInt56(ulong maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 56;
        return (ulong) (Sample() * maxValue);
    }
    public ulong NextUInt56(ulong minValue, ulong maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        BitWidth = 56;
        return (uint) Next(minValue, maxValue);
    }
    public long NextInt56()
    {
        if (Unsigned)
            Unsigned = false;
        BitWidth = 56;
        return (long) Internal();
    }
    public long NextInt56(long maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 56;
        return (long) (Sample() * maxValue);
    }
    public long NextInt56(long minValue, long maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        BitWidth = 48;
        return (long) Next(minValue, maxValue);
    }
    public long NextInt64()
    {
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 64)
            BitWidth = 64;
        return (long) Internal();
    }
    public long NextInt64(long maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 64)
            BitWidth = 64;
        return (long) (Sample() * maxValue);
    }
    public long NextInt64(long minValue, long maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (Unsigned)
            Unsigned = false;
        if (_bitWidth < 64)
            BitWidth = 64;
        return (long) Next(minValue, maxValue);
    }
    public ulong NextUInt64()
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 64)
            BitWidth = 64;
        return (ulong) Internal();
    }
    public ulong NextUInt64(ulong maxValue)
    {
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 64)
            BitWidth = 64;
        return (ulong) (Sample() * maxValue);
    }
    public ulong NextUInt64(ulong minValue, ulong maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        if (!Unsigned)
            Unsigned = true;
        if (_bitWidth < 64)
            BitWidth = 64;
        return (ulong) Next(minValue, maxValue);
    }
    public BigInteger Next()
    {
        return Internal();
    }
    public BigInteger Next(BigInteger minValue, BigInteger maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        return (BigInteger) (Sample() * (maxValue - minValue)) + minValue;
    }
    public UInt512 Next(UInt512 minValue, UInt512 maxValue)
    {
        if (minValue > maxValue)
            throw new ArgumentException("maxValue must be greater than or equal to minValue");
        var s = Sample();
        var f = (BigDecimal) ((BigInteger) maxValue - (BigInteger) minValue);
        return (BigInteger) (s * f);
    }
    public BigInteger Next(BigInteger maxValue)
    {
        if (maxValue < 0)
            throw new ArgumentException("maxValue must be greater than zero.");
        return (BigInteger) (Sample() * maxValue);
    }
    public unsafe double NextDouble()
    {
        var buf = new byte[8];
        GetBytes(buf);
        fixed (byte* ptr = buf)
        {
            return *(ulong*) ptr * (1.0 / ulong.MaxValue) * ulong.MaxValue;
        }
    }
    public BigRational NextBigRational()
    {
        return new BigRational(Internal(), Internal());
    }
    public decimal NextDecimal()
    {
        return new decimal(NextInt32(), NextInt32(), NextInt32(), NextBool(), NextUInt8(255));
    }
    public BigDecimal NextBigDecimal()
    {
        return Sample();
    }
    public byte[] GetNextByteArray(int size)
    {
        var ba = new byte[size];
        _crng.GetBytes(ba);
        return ba;
    }
    public char[] GetNextCharArray(int size)
    {
        var xbc = new byte[1];
        var ca  = new char[size];
        var ptr = 0;
        do
        {
            _crng.GetBytes(xbc);
            var c = xbc[0];
            if (c >= 0x20 && c <= 0x7F)
                ca[ptr++] = (char) c;
        } while (ptr < size);
        return ca;
    }
    public char NextChar()
    {
        var xbc = new byte[1];
        while (true)
        {
            _crng.GetBytes(xbc);
            var c = xbc[0];
            if (c >= 0x20 && c <= 0x7F)
                return (char) c;
        }
    }
    public string GetRandomString(int minLen, int maxLen)
    {
        return minLen == maxLen ? new string(GetNextCharArray(minLen)) : new string(GetNextCharArray((int) NextUInt32((uint) minLen, (uint) maxLen)));
    }
    private BigDecimal Sample()
    {
        var i = Internal();
        var s = i * (BigDecimal.One / MaxValue);
        if (s.Sign == -1)
            s = s * -1;
        if (s.IsZero)
            throw new Exception("Sample is zero.");
        return s;
    }
    public void GetBytes(byte[] data)
    {
        if (data == null)
            throw new ArgumentException("The buffer cannot be null.");
        _crng.GetBytes(data);
    }
    private BigInteger Internal()
    {
        if (Unsigned)
        {
            var buffer = new byte[_maxByteWidth + 1];
            _crng.GetBytes(buffer);
            buffer[_maxByteWidth] = 0;
            var n = new BigInteger(buffer);
            return !OddsOnly ? n : n | 1;
        }
        else
        {
            var buffer = new byte[_maxByteWidth];
            _crng.GetBytes(buffer);
            var n = new BigInteger(buffer);
            return !OddsOnly ? n : n | 1;
        }
    }
}