// 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.

using System.Diagnostics.Contracts;
using System.Runtime.CompilerServices;

namespace CommunityToolkit.HighPerformance;

/// <summary>
/// Helpers for working with the <see cref="bool"/> type.
/// </summary>
public static class BoolExtensions
{
    /// <summary>
    /// Converts the given <see cref="bool"/> value into a <see cref="byte"/>.
    /// </summary>
    /// <param name="flag">The input value to convert.</param>
    /// <returns>1 if <paramref name="flag"/> is <see langword="true"/>, 0 otherwise.</returns>
    /// <remarks>This method does not contain branching instructions.</remarks>
    [Pure]
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static unsafe byte ToByte(this bool flag)
    {
        // Whenever we need to take the address of an argument, we make a local copy first.
        // This will be removed by the JIT anyway, but it can help produce better codegen and
        // remove unwanted stack spills if the caller is using constant arguments. This is
        // because taking the address of an argument can interfere with some of the flow
        // analysis executed by the JIT, which can in some cases block constant propagation.
        bool copy = flag;

        return *(byte*)&copy;
    }

    /// <summary>
    /// Converts the given <see cref="bool"/> value to an <see cref="int"/> mask with
    /// all bits representing the value of the input flag (either 0xFFFFFFFF or 0x00000000).
    /// </summary>
    /// <param name="flag">The input value to convert.</param>
    /// <returns>0xFFFFFFFF if <paramref name="flag"/> is <see langword="true"/>, 0x00000000 otherwise.</returns>
    /// <remarks>
    /// This method does not contain branching instructions, and it is only guaranteed to work with
    /// <see cref="bool"/> values being either 0 or 1. Operations producing a <see cref="bool"/> result,
    /// such as numerical comparisons, always result in a valid value. If the <see cref="bool"/> value is
    /// produced by fields with a custom <see cref="System.Runtime.InteropServices.FieldOffsetAttribute"/>,
    /// or by using <see cref="Unsafe.As{T}"/> or other unsafe APIs to directly manipulate the underlying
    /// data though, it is responsibility of the caller to ensure the validity of the provided value.
    /// </remarks>
    [Pure]
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static unsafe int ToBitwiseMask32(this bool flag)
    {
        bool copy = flag;
        byte rangeFlag = *(byte*)&copy;
        int negativeFlag = rangeFlag - 1;
        int mask = ~negativeFlag;

        return mask;
    }

    /// <summary>
    /// Converts the given <see cref="bool"/> value to a <see cref="long"/> mask with
    /// all bits representing the value of the input flag (either all 1s or 0s).
    /// </summary>
    /// <param name="flag">The input value to convert.</param>
    /// <returns>All 1s if <paramref name="flag"/> is <see langword="true"/>, all 0s otherwise.</returns>
    /// <remarks>This method does not contain branching instructions. See additional note in <see cref="ToBitwiseMask32"/>.</remarks>
    [Pure]
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static unsafe long ToBitwiseMask64(this bool flag)
    {
        bool copy = flag;
        byte rangeFlag = *(byte*)&copy;
        long negativeFlag = (long)rangeFlag - 1;
        long mask = ~negativeFlag;

        return mask;
    }
}