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using Ryujinx.Common.Memory;
using System;
using System.Buffers.Binary;
namespace Ryujinx.Graphics.Nvdec.Vp9.Dsp
{
internal struct Reader
{
private static readonly byte[] _norm = {
0, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};
private const int BdValueSize = sizeof(ulong) * 8;
// This is meant to be a large, positive constant that can still be efficiently
// loaded as an immediate (on platforms like ARM, for example).
// Even relatively modest values like 100 would work fine.
private const int LotsOfBits = 0x40000000;
public ulong Value;
public uint Range;
public int Count;
private ArrayPtr<byte> _buffer;
public bool Init(ArrayPtr<byte> buffer, int size)
{
if (size != 0 && buffer.IsNull)
{
return true;
}
else
{
_buffer = new ArrayPtr<byte>(ref buffer[0], size);
Value = 0;
Count = -8;
Range = 255;
Fill();
return ReadBit() != 0; // Marker bit
}
}
private void Fill()
{
ReadOnlySpan<byte> buffer = _buffer.AsSpan();
ReadOnlySpan<byte> bufferStart = buffer;
ulong value = Value;
int count = Count;
ulong bytesLeft = (ulong)buffer.Length;
ulong bitsLeft = bytesLeft * 8;
int shift = BdValueSize - 8 - (count + 8);
if (bitsLeft > BdValueSize)
{
int bits = (shift & unchecked((int)0xfffffff8)) + 8;
ulong nv;
ulong bigEndianValues = BinaryPrimitives.ReadUInt64BigEndian(buffer);
nv = bigEndianValues >> (BdValueSize - bits);
count += bits;
buffer = buffer[(bits >> 3)..];
value = Value | (nv << (shift & 0x7));
}
else
{
int bitsOver = shift + 8 - (int)bitsLeft;
int loopEnd = 0;
if (bitsOver >= 0)
{
count += LotsOfBits;
loopEnd = bitsOver;
}
if (bitsOver < 0 || bitsLeft != 0)
{
while (shift >= loopEnd)
{
count += 8;
value |= (ulong)buffer[0] << shift;
buffer = buffer[1..];
shift -= 8;
}
}
}
// NOTE: Variable 'buffer' may not relate to '_buffer' after decryption,
// so we increase '_buffer' by the amount that 'buffer' moved, rather than
// assign 'buffer' to '_buffer'.
_buffer = _buffer.Slice(bufferStart.Length - buffer.Length);
Value = value;
Count = count;
}
public readonly bool HasError()
{
// Check if we have reached the end of the buffer.
//
// Variable 'count' stores the number of bits in the 'value' buffer, minus
// 8. The top byte is part of the algorithm, and the remainder is buffered
// to be shifted into it. So if count == 8, the top 16 bits of 'value' are
// occupied, 8 for the algorithm and 8 in the buffer.
//
// When reading a byte from the user's buffer, count is filled with 8 and
// one byte is filled into the value buffer. When we reach the end of the
// data, count is additionally filled with LotsOfBits. So when
// count == LotsOfBits - 1, the user's data has been exhausted.
//
// 1 if we have tried to decode bits after the end of stream was encountered.
// 0 No error.
return Count > BdValueSize && Count < LotsOfBits;
}
public int Read(int prob)
{
uint bit = 0;
ulong value;
ulong bigsplit;
int count;
uint range;
uint split = (Range * (uint)prob + (256 - (uint)prob)) >> 8;
if (Count < 0)
{
Fill();
}
value = Value;
count = Count;
bigsplit = (ulong)split << (BdValueSize - 8);
range = split;
if (value >= bigsplit)
{
range = Range - split;
value -= bigsplit;
bit = 1;
}
{
int shift = _norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
Value = value;
Count = count;
Range = range;
return (int)bit;
}
public int ReadBit()
{
return Read(128); // vpx_prob_half
}
public int ReadLiteral(int bits)
{
int literal = 0, bit;
for (bit = bits - 1; bit >= 0; bit--)
{
literal |= ReadBit() << bit;
}
return literal;
}
public int ReadTree(ReadOnlySpan<sbyte> tree, ReadOnlySpan<byte> probs)
{
sbyte i = 0;
while ((i = tree[i + Read(probs[i >> 1])]) > 0)
{
}
return -i;
}
public int ReadBool(int prob, ref ulong value, ref int count, ref uint range)
{
uint split = (range * (uint)prob + (256 - (uint)prob)) >> 8;
ulong bigsplit = (ulong)split << (BdValueSize - 8);
if (count < 0)
{
Value = value;
Count = count;
Fill();
value = Value;
count = Count;
}
if (value >= bigsplit)
{
range -= split;
value -= bigsplit;
{
int shift = _norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
return 1;
}
range = split;
{
int shift = _norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
return 0;
}
public ArrayPtr<byte> FindEnd()
{
// Find the end of the coded buffer
while (Count > 8 && Count < BdValueSize)
{
Count -= 8;
_buffer = _buffer.Slice(-1);
}
return _buffer;
}
}
}
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