PKHeX/PKHeX.Core/Legality/RNG/RNG.cs

namespace PKHeX.Core
{
    public class RNG
    {
        public static readonly RNG LCRNG = new RNG(0x41C64E6D, 0x00006073, 0xEEB9EB65, 0x0A3561A1);
        public static readonly RNG XDRNG = new RNG(0x000343FD, 0x00269EC3, 0xB9B33155, 0xA170F641);
        public static readonly RNG ARNG  = new RNG(0x6C078965, 0x00000001, 0x9638806D, 0x69C77F93);

        private readonly uint Mult, Add, rMult, rAdd;
        private RNG(uint f_mult, uint f_add, uint r_mult, uint r_add)
        {
            Mult = f_mult;
            Add = f_add;
            rMult = r_mult;
            rAdd = r_add;
        }

        public uint Next(uint seed) => seed * Mult + Add;
        public uint Prev(uint seed) => seed * rMult + rAdd;

        public uint Advance(uint seed, int frames)
        {
            for (int i = 0; i < frames; i++)
                seed = Next(seed);
            return seed;
        }
        public uint Reverse(uint seed, int frames)
        {
            for (int i = 0; i < frames; i++)
                seed = Prev(seed);
            return seed;
        }

        /// <summary>
        /// Generates an IV for each RNG call using the top 5 bits of frame seeds.
        /// </summary>
        /// <param name="seed">RNG seed</param>
        /// <returns>Array of 6 IVs</returns>
        internal uint[] GetSequentialIVsUInt32(uint seed)
        {
            uint[] ivs = new uint[6];
            for (int i = 0; i < 6; i++)
            {
                seed = Next(seed);
                ivs[i] = seed >> 27;
            }
            return ivs;
        }
        internal int[] GetSequentialIVsInt32(uint seed)
        {
            int[] ivs = new int[6];
            for (int i = 0; i < 6; i++)
            {
                seed = Next(seed);
                ivs[i] = (int)(seed >> 27);
            }
            return ivs;
        }
    }
}