PKHeX/PKHeX.Core/Util/FlagUtil.cs

using System;

namespace PKHeX.Core
{
    /// <summary>
    /// Utility logic for dealing with bitflags in a byte array.
    /// </summary>
    public static class FlagUtil
    {
        /// <summary>
        /// Gets the requested <see cref="bitIndex"/> from the byte at <see cref="offset"/>.
        /// </summary>
        /// <param name="arr">Buffer to read</param>
        /// <param name="offset">Offset of the byte</param>
        /// <param name="bitIndex">Bit to read</param>
        public static bool GetFlag(ReadOnlySpan<byte> arr, int offset, int bitIndex)
        {
            bitIndex &= 7; // ensure bit access is 0-7
            return (arr[offset] >> bitIndex & 1) != 0;
        }

        /// <summary>
        /// Sets the requested <see cref="bitIndex"/> value to the byte at <see cref="offset"/>.
        /// </summary>
        /// <param name="arr">Buffer to modify</param>
        /// <param name="offset">Offset of the byte</param>
        /// <param name="bitIndex">Bit to write</param>
        /// <param name="value">Bit flag value to set</param>
        public static void SetFlag(Span<byte> arr, int offset, int bitIndex, bool value)
        {
            bitIndex &= 7; // ensure bit access is 0-7
            var current = arr[offset] & ~(1 << bitIndex);
            var newValue = current | ((value ? 1 : 0) << bitIndex);
            arr[offset] = (byte)newValue;
        }
    }
}