ryujinx/Ryujinx.Graphics.Texture/Astc/BitStream128.cs

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using Ryujinx.Common.Utilities;
using System;
using System.Diagnostics;
namespace Ryujinx.Graphics.Texture.Astc
{
public struct BitStream128
{
private Buffer16 _data;
public int BitsLeft { get; set; }
public BitStream128(Buffer16 data)
{
_data = data;
BitsLeft = 128;
}
public int ReadBits(int bitCount)
{
Debug.Assert(bitCount < 32);
if (bitCount == 0)
{
return 0;
}
int mask = (1 << bitCount) - 1;
int value = _data.As<int>() & mask;
Span<ulong> span = _data.AsSpan<ulong>();
ulong carry = span[1] << (64 - bitCount);
span[0] = (span[0] >> bitCount) | carry;
span[1] >>= bitCount;
BitsLeft -= bitCount;
return value;
}
public void WriteBits(int value, int bitCount)
{
Debug.Assert(bitCount < 32);
if (bitCount == 0) return;
ulong maskedValue = (uint)(value & ((1 << bitCount) - 1));
Span<ulong> span = _data.AsSpan<ulong>();
if (BitsLeft < 64)
{
ulong lowMask = maskedValue << BitsLeft;
span[0] |= lowMask;
}
if (BitsLeft + bitCount > 64)
{
if (BitsLeft > 64)
{
span[1] |= maskedValue << (BitsLeft - 64);
}
else
{
span[1] |= maskedValue >> (64 - BitsLeft);
}
}
BitsLeft += bitCount;
}
}
}