public PageTrailer(byte[] buffer, int offset)
{
ptype = (PageTypeName)buffer[offset + 0];
PageTypeName ptypeRepeat = (PageTypeName)buffer[offset + 1];
wSig = LittleEndianConverter.ToUInt16(buffer, offset + 2);
dwCRC = LittleEndianConverter.ToUInt32(buffer, offset + 4);
bid = new BlockID(buffer, offset + 8);
}
public static BTreeIndexPage GetEmptyIndexPage(PageTypeName pageType, int cLevel)
{
BTreeIndexPage page = new BTreeIndexPage();
page.pageTrailer.ptype = pageType;
page.cbEnt = BTreeIndexEntry.Length;
page.cEntMax = MaximumNumberOfEntries;
page.cLevel = (byte)cLevel;
return(page);
}
public static BTreePage ReadFromStream(Stream stream, BlockRef blockRef)
{
long offset = (long)blockRef.ib;
stream.Seek(offset, SeekOrigin.Begin);
byte[] buffer = new byte[Length];
stream.Read(buffer, 0, Length);
PageTypeName ptype = (PageTypeName)buffer[PageTrailer.OffsetFromPageStart + 0];
BTreePage page;
byte cLevel = buffer[491];
if (cLevel > 0)
{
// If cLevel is greater than 0, then each entry in the array is of type BTENTRY.
page = new BTreeIndexPage(buffer);
}
else
{
// If cLevel is 0, then each entry is either of type BBTENTRY or NBTENTRY, depending on the ptype of the page.
if (ptype == PageTypeName.ptypeBBT)
{
page = new BlockBTreeLeafPage(buffer);
}
else if (ptype == PageTypeName.ptypeNBT)
{
page = new NodeBTreeLeafPage(buffer);
}
else
{
throw new ArgumentException("BTreePage has incorrect ptype");
}
}
page.Offset = (ulong)blockRef.ib;
if (blockRef.bid.Value != page.BlockID.Value)
{
throw new InvalidBlockIDException();
}
uint crc = PSTCRCCalculation.ComputeCRC(buffer, PageTrailer.OffsetFromPageStart);
if (page.pageTrailer.dwCRC != crc)
{
throw new InvalidChecksumException();
}
uint signature = BlockTrailer.ComputeSignature(blockRef.ib, blockRef.bid.Value);
if (page.pageTrailer.wSig != signature)
{
throw new InvalidChecksumException();
}
return(page);
}
