// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable enable

// NOTE: This code is derived from an implementation originally in dotnet/runtime:
// https://github.com/dotnet/runtime/blob/v8.0.3/src/libraries/Common/src/System/Collections/Generic/BitHelper.cs
//
// See the commentary in https://github.com/dotnet/roslyn/pull/50156 for notes on incorporating changes made to the
// reference implementation.

using System;
using System.Diagnostics;

namespace Microsoft.CodeAnalysis.Collections.Internal
{
    internal ref struct BitHelper
    {
        private const int IntSize = sizeof(int) * 8;
        private readonly Span<int> _span;

        internal BitHelper(Span<int> span, bool clear)
        {
            if (clear)
            {
                span.Clear();
            }
            _span = span;
        }

        internal readonly void MarkBit(int bitPosition)
        {
            Debug.Assert(bitPosition >= 0);

            uint bitArrayIndex = (uint)bitPosition / IntSize;

            // Workaround for https://github.com/dotnet/runtime/issues/72004
            Span<int> span = _span;
            if (bitArrayIndex < (uint)span.Length)
            {
                span[(int)bitArrayIndex] |= (1 << (int)((uint)bitPosition % IntSize));
            }
        }

        internal readonly bool IsMarked(int bitPosition)
        {
            Debug.Assert(bitPosition >= 0);

            uint bitArrayIndex = (uint)bitPosition / IntSize;

            // Workaround for https://github.com/dotnet/runtime/issues/72004
            Span<int> span = _span;
            return
                bitArrayIndex < (uint)span.Length &&
                (span[(int)bitArrayIndex] & (1 << ((int)((uint)bitPosition % IntSize)))) != 0;
        }

        /// <summary>How many ints must be allocated to represent n bits. Returns (n+31)/32, but avoids overflow.</summary>
        internal static int ToIntArrayLength(int n) => n > 0 ? ((n - 1) / IntSize + 1) : 0;
    }
}