/// <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));
}
/// <summary>
/// One shot hash calculation for a given data.
/// </summary>
/// <param name="data">Data to be hashed</param>
/// <returns>Hash of the given data</returns>
public static uint CalcHash(ReadOnlySpan <byte> data)
{
HashState state = new HashState();
state.Initialize();
state.Continue(data);
return(state.Finalize(data));
}
/// <summary>
/// Gets an existing item from the table, or adds a new one if not present.
/// </summary>
/// <param name="data">Data</param>
/// <param name="item">Item associated with the data</param>
/// <returns>Existing item, or <paramref name="item"/> if not present</returns>
public T GetOrAdd(byte[] data, T item)
{
SizeEntry sizeEntry;
int index = BinarySearch(_sizeTable, data.Length);
if (index < _sizeTable.Count && _sizeTable[index].Size == data.Length)
{
sizeEntry = _sizeTable[index];
}
else
{
if (index < _sizeTable.Count && _sizeTable[index].Size < data.Length)
{
index++;
}
sizeEntry = new SizeEntry(data.Length);
_sizeTable.Insert(index, sizeEntry);
for (int i = index + 1; i < _sizeTable.Count; i++)
{
_sizeTable[i].FillPartials(sizeEntry);
}
}
HashState hashState = new HashState();
hashState.Initialize();
for (int i = 0; i < index; i++)
{
ReadOnlySpan <byte> dataSlice = new ReadOnlySpan <byte>(data).Slice(0, _sizeTable[i].Size);
hashState.Continue(dataSlice);
_sizeTable[i].AddPartial(data, hashState.Finalize(dataSlice));
}
hashState.Continue(data);
return(sizeEntry.GetOrAdd(data, hashState.Finalize(data), item));
}
/// <summary>
/// Adds a partial entry to the hash table.
/// </summary>
/// <param name="ownerData">Full data</param>
/// <param name="ownSize">Size of the sub-region of <paramref name="ownerData"/> used by the partial entry</param>
/// <returns>True if added, false otherwise</returns>
public bool AddPartial(byte[] ownerData, int ownSize)
{
ReadOnlySpan <byte> data = new ReadOnlySpan <byte>(ownerData).Slice(0, ownSize);
return(AddPartial(ownerData, HashState.CalcHash(data), ownSize));
}
