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using System;
using System.Collections.Generic;
namespace Ryujinx.Graphics.Gpu.Shader.HashTable
{
/// <summary>
/// Smart data accessor that can cache data and hashes to avoid reading and re-hashing the same memory regions.
/// </summary>
ref struct SmartDataAccessor
{
private readonly IDataAccessor _dataAccessor;
private ReadOnlySpan<byte> _data;
private readonly SortedList<int, HashState> _cachedHashes;
/// <summary>
/// Creates a new smart data accessor.
/// </summary>
/// <param name="dataAccessor">Data accessor</param>
public SmartDataAccessor(IDataAccessor dataAccessor)
{
_dataAccessor = dataAccessor;
_data = ReadOnlySpan<byte>.Empty;
_cachedHashes = new SortedList<int, HashState>();
}
/// <summary>
/// Get a spans of a given size.
/// </summary>
/// <remarks>
/// The actual length of the span returned depends on the <see cref="IDataAccessor"/>
/// and might be less than requested.
/// </remarks>
/// <param name="length">Size in bytes</param>
/// <returns>Span with the requested size</returns>
public ReadOnlySpan<byte> GetSpan(int length)
{
if (_data.Length < length)
{
_data = _dataAccessor.GetSpan(0, length);
}
else if (_data.Length > length)
{
return _data.Slice(0, length);
}
return _data;
}
/// <summary>
/// Gets a span of the requested size, and a hash of its data.
/// </summary>
/// <param name="length">Length of the span</param>
/// <param name="hash">Hash of the span data</param>
/// <returns>Span of data</returns>
public ReadOnlySpan<byte> GetSpanAndHash(int length, out uint hash)
{
ReadOnlySpan<byte> data = GetSpan(length);
hash = data.Length == length ? CalcHashCached(data) : 0;
return data;
}
/// <summary>
/// Calculates the hash for a requested span.
/// This will try to use a cached hash if the data was already accessed before, to avoid re-hashing.
/// </summary>
/// <param name="data">Data to be hashed</param>
/// <returns>Hash of the data</returns>
private uint CalcHashCached(ReadOnlySpan<byte> data)
{
HashState state = default;
bool found = false;
for (int i = _cachedHashes.Count - 1; i >= 0; i--)
{
int cachedHashSize = _cachedHashes.Keys[i];
if (cachedHashSize < data.Length)
{
state = _cachedHashes.Values[i];
found = true;
break;
}
}
if (!found)
{
state = new HashState();
state.Initialize();
}
state.Continue(data);
_cachedHashes[data.Length & ~7] = state;
return state.Finalize(data);
}
}
}
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