Hastlayer-SDK

namespace Hast.Algorithms.Random;

/// <summary>
/// A very simple pseudo random number generator implemented with a <see
/// href="https://en.wikipedia.org/wiki/Linear_feedback_shift_register">linear-feedback shift register</see>. Use this
/// if you want simple but fast PRNG with the least resources. For a PRNG that has better quality but higher resource
/// usage see <see cref="RandomMwc64X"/>.
/// </summary>
public class RandomLfsr
{
    /// <summary>
    /// Gets or sets the current inner state of the random number generator. If you set it when instantiating the object
    /// then it'll serve as a seed.
    /// </summary>
    /// <remarks>
    /// <para>By not using a constructor the whole class can be inlined for maximal performance.</para>
    /// </remarks>
    public uint State { get; set; } = 498_113; // Just some starting number.

    public uint NextUInt32()
    {
        // Using the taps from https://www.xilinx.com/support/documentation/application_notes/xapp052.pdf
        uint tapBits = (State >> 0) ^ (State >> 10) ^ (State >> 30) ^ (State >> 31);
        // Could also be
        //// uint tapBits = State >> 0 ^ State >> 2 ^ State >> 6 ^ State >> 7;
        // according to the taps here:
        // https://web.archive.org/web/20161007061934/http://courses.cse.tamu.edu/csce680/walker/lfsr_table.pdf

        State = (State >> 1) | (tapBits << 31);
        return State;
    }
}