BitStack.cs

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using System.Runtime.CompilerServices;
 
namespace System.Text.Json;
 
internal struct BitStack
{
    private int[] _array;
 
    private ulong _allocationFreeContainer;
 
    private int _currentDepth;
 
    public int CurrentDepth => _currentDepth;
 
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public void PushTrue()
    {
        if (_currentDepth < 64)
        {
            _allocationFreeContainer = (_allocationFreeContainer << 1) | 1;
        }
        else
        {
            PushToArray(value: true);
        }
        _currentDepth++;
    }
 
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public void PushFalse()
    {
        if (_currentDepth < 64)
        {
            _allocationFreeContainer <<= 1;
        }
        else
        {
            PushToArray(value: false);
        }
        _currentDepth++;
    }
 
    [MethodImpl(MethodImplOptions.NoInlining)]
    private void PushToArray(bool value)
    {
        if (_array == null)
        {
            _array = new int[2];
        }
        int number = _currentDepth - 64;
        int remainder;
        int num = Div32Rem(number, out remainder);
        if (num >= _array.Length)
        {
            DoubleArray(num);
        }
        int num2 = _array[num];
        num2 = ((!value) ? (num2 & ~(1 << remainder)) : (num2 | (1 << remainder)));
        _array[num] = num2;
    }
 
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public bool Pop()
    {
        _currentDepth--;
        bool flag = false;
        if (_currentDepth < 64)
        {
            _allocationFreeContainer >>= 1;
            return (_allocationFreeContainer & 1) != 0;
        }
        if (_currentDepth == 64)
        {
            return (_allocationFreeContainer & 1) != 0;
        }
        return PopFromArray();
    }
 
    [MethodImpl(MethodImplOptions.NoInlining)]
    private bool PopFromArray()
    {
        int number = _currentDepth - 64 - 1;
        int remainder;
        int num = Div32Rem(number, out remainder);
        return (_array[num] & (1 << remainder)) != 0;
    }
 
    private void DoubleArray(int minSize)
    {
        int newSize = Math.Max(minSize + 1, _array.Length * 2);
        Array.Resize(ref _array, newSize);
    }
 
    public void SetFirstBit()
    {
        _currentDepth++;
        _allocationFreeContainer = 1uL;
    }
 
    public void ResetFirstBit()
    {
        _currentDepth++;
        _allocationFreeContainer = 0uL;
    }
 
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static int Div32Rem(int number, out int remainder)
    {
        uint result = (uint)number / 32u;
        remainder = number & 0x1F;
        return (int)result;
    }
}