/// <summary>
/// Perform lookup for byte string at position.
/// </summary>
/// <param name="src">Source buffer.</param>
/// <param name="position">Position in source buffer.</param>
/// <param name="window">Deltas window.</param>
/// <param name="recents">Recents buffer.</param>
/// <returns></returns>
static LookupResult Lookup(
ReadOnlySpan <byte> src,
int position,
ref RevolvingBufferTracker <int> window,
Span <int> recents)
{
// Get offset to previous index of current byte value.
var c = src[position];
var recent = recents[c] - 1;
// Check if: recent is 0 (no previous byte with this value), or offset is out-of-range of window.
if (recent < 0 || window.Length < (position - recent))
{
return(LookupResult.NoneFound());
}
else
{
// Start searching at recent position.
var searchPosition = recent;
var currentSlice = src.Slice(position, Math.Min(MaxCompare, src.Length - position));
var windowStartPosition = Math.Max(position - window.Length, 0);
var result = LookupResult.NoneFound();
// Follow chain backwards and look for matches.
while (windowStartPosition <= searchPosition)
{
// Get slice for bytes to compare against currentSlice
var searchSlice = src.Slice(searchPosition);
// Find number of potential matches in search slice.
var potentialMatches = Math.Min(currentSlice.Length, searchSlice.Length);
// Set matches count to maximum, will update if loop exits early.
var matches = potentialMatches;
for (int i = 0; i < potentialMatches; i++)
{
if (currentSlice[i] != searchSlice[i])
{
matches = i;
break;
}
}
// Update lookup result if found new longest match.
if (matches >= 3 && matches >= result.Length)
{
result = new LookupResult(searchPosition, matches);
// If we have found a matching string with the max compare size, return early.
if (result.Length == MaxCompare)
{
break;
}
}
// Get search position relative to window start, and update search position.
var windowIndex = searchPosition - windowStartPosition;
searchPosition = window.Get(windowIndex);
// If next index is less-than 0, no previous instance of this value.
if (searchPosition < 0)
{
break;
}
}
return(result);
}
}
