// 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;
using System.Diagnostics.CodeAnalysis;
 
namespace Microsoft.CodeAnalysis.Shared.Utilities;
 
internal static class IntegerUtilities
{
    public static int CountOfBitsSet(long v)
    {
        // http://graphics.stanford.edu/~seander/bithacks.htm
        var c = 0;
        while (v != 0)
        {
            // clear the least significant bit set
            v &= unchecked(v - 1);
            c++;
        }
 
        return c;
    }
 
    public static bool HasOneBitSet(IComparable value)
    {
        switch (value)
        {
            case long v: return HasOneBitSet(v);
            case ulong v: return HasOneBitSet(unchecked((long)v));
            case int v: return HasOneBitSet(v);
            case uint v: return HasOneBitSet(v);
            case short v: return HasOneBitSet(v);
            case ushort v: return HasOneBitSet(v);
            case sbyte v: return HasOneBitSet(v);
            case byte v: return HasOneBitSet(v);
            default: return false;
        }
    }
 
    public static bool HasOneBitSet(long v)
        => CountOfBitsSet(v) == 1;
 
    public static int LogBase2(long v)
    {
        var log = 0;
 
        while ((v >>= 1) != 0)
        {
            log++;
        }
 
        return log;
    }
 
    /// <summary>
    /// Helper as VB's CType doesn't work without arithmetic overflow.
    /// </summary>
    public static long Convert(long v, SpecialType type)
        => type switch
        {
            SpecialType.System_SByte => unchecked((sbyte)v),
            SpecialType.System_Byte => unchecked((byte)v),
            SpecialType.System_Int16 => unchecked((short)v),
            SpecialType.System_UInt16 => unchecked((ushort)v),
            SpecialType.System_Int32 => unchecked((int)v),
            SpecialType.System_UInt32 => unchecked((uint)v),
            _ => v,
        };
 
    public static ulong ToUnsigned(long v)
        => unchecked((ulong)v);
 
    public static ulong ToUInt64(object? o)
        => o is ulong ? (ulong)o : unchecked((ulong)System.Convert.ToInt64(o));
 
    public static long ToInt64(object? o)
        => o is ulong ul ? unchecked((long)ul) : System.Convert.ToInt64(o);
 
    public static bool IsIntegral([NotNullWhen(true)] object? value)
        => value switch
        {
            sbyte _ => true,
            byte _ => true,
            short _ => true,
            ushort _ => true,
            int _ => true,
            uint _ => true,
            long _ => true,
            ulong _ => true,
            _ => false,
        };
}