// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

namespace Microsoft.AspNet.Server.Kestrel.Extensions
{
    public static class LongExtensions
    {
        public static int BitCount(this long value)
        {
            // see https://github.com/dotnet/corefx/blob/master/src/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/BitArithmetic.cs

            const ulong Mask01010101 = 0x5555555555555555UL;
            const ulong Mask00110011 = 0x3333333333333333UL;
            const ulong Mask00001111 = 0x0F0F0F0F0F0F0F0FUL;
            const ulong Mask00000001 = 0x0101010101010101UL;

            var v = (ulong)value;

            v = v - ((v >> 1) & Mask01010101);
            v = (v & Mask00110011) + ((v >> 2) & Mask00110011);
            return (int)(unchecked(((v + (v >> 4)) & Mask00001111) * Mask00000001) >> 56);
        }
    }
}