private void AddSharedEntry(int hashCode, SharedEntryValue e)
{
var arr = _sharedTableInst;
int idx = SharedIdxFromHash(hashCode);
// try finding an empty spot in the bucket
// we use quadratic probing here
// bucket positions are (n^2 + n)/2 relative to the masked hashcode
int curIdx = idx;
for (int i = 1; i < SharedBucketSize + 1; i++)
{
if (arr[curIdx].Entry == null)
{
idx = curIdx;
goto foundIdx;
}
curIdx = (curIdx + i) & SharedSizeMask;
}
// or pick a random victim within the bucket range
// and replace with new entry
var i1 = NextRandom() & SharedBucketSizeMask;
idx = (idx + ((i1 * i1 + i1) / 2)) & SharedSizeMask;
foundIdx:
arr[idx].HashCode = hashCode;
Volatile.Write(ref arr[idx].Entry, e);
}
private SharedEntryValue FindSharedEntry(char[] chars, int start, int len, int hashCode)
{
var arr = _sharedTableInst;
int idx = SharedIdxFromHash(hashCode);
SharedEntryValue e = null;
// we use quadratic probing here
// bucket positions are (n^2 + n)/2 relative to the masked hashcode
for (int i = 1; i < SharedBucketSize + 1; i++)
{
e = arr[idx].Entry;
int hash = arr[idx].HashCode;
if (e != null)
{
if (hash == hashCode && StringTable.TextEquals(e.Text, chars, start, len))
{
break;
}
// this is not e we are looking for
e = null;
}
else
{
// once we see unfilled entry, the rest of the bucket will be empty
break;
}
idx = (idx + i) & SharedSizeMask;
}
return(e);
}
internal T FindItem(char[] chars, int start, int len, int hashCode)
{
// capture array to avoid extra range checks
var arr = _localTable;
var idx = LocalIdxFromHash(hashCode);
var text = arr[idx].Text;
if (text != null && arr[idx].HashCode == hashCode)
{
if (StringTable.TextEquals(text, chars, start, len))
{
return(arr[idx].Item);
}
}
SharedEntryValue e = FindSharedEntry(chars, start, len, hashCode);
if (e != null)
{
// PERF: the following code does element-wise assignment of a struct
// because current JIT produces better code compared to
// arr[idx] = new LocalEntry(...)
arr[idx].HashCode = hashCode;
arr[idx].Text = e.Text;
var tk = e.Item;
arr[idx].Item = tk;
return(tk);
}
return(null);
}
internal void AddItem(char[] chars, int start, int len, int hashCode, T item)
{
var text = _strings.Add(chars, start, len);
// add to the shared table first (in case someone looks for same item)
var e = new SharedEntryValue(text, item);
AddSharedEntry(hashCode, e);
// add to the local table too
var arr = _localTable;
var idx = LocalIdxFromHash(hashCode);
arr[idx].HashCode = hashCode;
arr[idx].Text = text;
arr[idx].Item = item;
}
