private IEnumerable <T> ReadBTHIndexHelper <T>(List <HNDataBlock> blocks, HID hid, int level)
{
if (level == 0)
{
int recCount = HidSize(blocks, hid) / Marshal.SizeOf(typeof(T));
if (hid.GetIndex(ndb.IsUnicode4K) != 0)
{
// The T record also forms the key of the BTH entry
foreach (var row in MapArray <T>(blocks, hid, recCount))
{
yield return(row);
}
}
}
else
{
int recCount = HidSize(blocks, hid) / Marshal.SizeOf(typeof(IntermediateBTH4));
var inters = MapArray <IntermediateBTH4>(blocks, hid, recCount);
foreach (var inter in inters)
{
foreach (var row in ReadBTHIndexHelper <T>(blocks, inter.hidNextLevel, level - 1))
{
yield return(row);
}
}
}
yield break; // No more entries
}
// Walk a b-tree implemented on a heap, and return all the type T entries
// This is used when reading the index of properties in a PC (property context), or rows in a TC (table context)
private IEnumerable <T> ReadBTHIndex <T>(List <HNDataBlock> blocks, HID hid)
{
var b = MapType <BTHHEADER>(blocks, hid);
foreach (var row in ReadBTHIndexHelper <T>(blocks, b.hidRoot, b.bIdxLevels))
{
yield return(row);
}
yield break; // No more entries
}
// Dereference the supplied HID in the supplied heap-on-node blocks,
// and return the size of the resulting data buffer
private int HidSize(List <HNDataBlock> blocks, HID hid)
{
var index = hid.GetIndex(ndb.IsUnicode4K);
if (index == 0) // Check for empty
{
return(0);
}
var b = blocks[hid.GetBlockIndex(ndb.IsUnicode4K)];
return(b.rgibAlloc[index] - b.rgibAlloc[index - 1]);
}
// Dereference the supplied HID in the supplied heap-on-node blocks,
// and map the resulting data buffer onto an array of count occurrences of the specified type T
private T[] MapArray <T>(List <HNDataBlock> blocks, HID hid, int count, int offset = 0)
{
var b = blocks[hid.GetBlockIndex(ndb.IsUnicode4K)];
return(Map.MapArray <T>(b.Buffer, b.rgibAlloc[hid.GetIndex(ndb.IsUnicode4K) - 1] + offset, count));
}