/// <summary>
/// Write page from buffer: n - page number; nbuf - buffer number
/// !!! NOT APPLICABLE TO IMO
/// </summary>
/// <param name="n"></param>
/// <param name="nbuf"></param>
private void page_write(long n, int nbuf)
{
for (int i = 0; i < pd.Length; i++)
{
if ((n >= pd[i].start_page) & (n <= pd[i].end_page))
{
long addr = (long)((n - pd[i].start_page) * (DESCRIPTOR.PageSize + DEFS.SYSTEM_USED_PAGE_SPACE));
uint crc32 = VSCRC32.CountCrc(segment_table[0].cache[nbuf].buf);
pd[i].fs.Write(addr + 4, crc32); // CRC32
if (DESCRIPTOR.CATALOG.ENCRYPT)
{
pd[i].fs.Write(addr, DEFS.DATA_ENCRYPTED); // Encryption
VSCrypto.Encrypt(ref segment_table[0].cache[nbuf].buf, ref e_buf, e_key, 0);
pd[i].fs.Write(addr + DEFS.SYSTEM_USED_PAGE_SPACE, ref e_buf);
}
else
{
pd[i].fs.Write(addr, DEFS.DATA_NOT_ENCRYPTED); // Encryption
pd[i].fs.Write(addr + DEFS.SYSTEM_USED_PAGE_SPACE, ref segment_table[0].cache[nbuf].buf);
}
PGWrite++;
}
}
}
/// <summary>
/// Calculate CRC32
/// </summary>
/// <param name="position">Start position, -1 - from the current position</param>
/// <param name="length">Length, -1 to end of stream</param>
/// <returns></returns>
public uint GetCRC32(long position, long length)
{
const int chunk = 1024;
// Save position
long save_pos = fs.Position;
// Calculate pos
long pos = (position < 0) ? fs.Position : position;
if (pos >= fs.Length)
{
pos = 0;
}
// Calculate len
long len = (length < 0) ? (fs.Length - pos) : length;
if ((pos + len) > fs.Length)
{
len = fs.Length - pos;
}
if (len == 0)
{
return(0);
}
// Calculate CRC32
uint c = VSCRC32.BeginCRC();
byte[] b = new byte[chunk];
fs.Seek(pos, SeekOrigin.Begin);
while (len > 0)
{
int l = (int)((len <= chunk) ? len : chunk);
this.ReadBytes(0, l);
c = VSCRC32.AddCRC(c, b);
len -= l;
}
// Restore position
fs.Seek(save_pos, SeekOrigin.Begin);
return(VSCRC32.EndCRC(c));
}
/// <summary>
/// Read page into buffer: n - page number; nbuf - buffer number
/// !!! NOT APPLICABLE TO IMO
/// </summary>
/// <param name="n"></param>
/// <param name="nbuf"></param>
private void page_read(long n, int sg, int pg, int nbuf)
{
for (int i = 0; i < pd.Length; i++)
{
if ((n >= pd[i].start_page) & (n <= pd[i].end_page))
{
// Absolute address (beginning of system area
long addr = (long)((n - pd[i].start_page) * (DESCRIPTOR.PageSize + DEFS.SYSTEM_USED_PAGE_SPACE));
uint encr = pd[i].fs.ReadUInt(addr); // Encryption
uint old_crc = pd[i].fs.ReadUInt(addr + 4); // Crc32
if (encr == DEFS.DATA_ENCRYPTED)
{
e_buf = pd[i].fs.ReadBytes(addr + DEFS.SYSTEM_USED_PAGE_SPACE, (int)page_size);
VSCrypto.Decrypt(ref e_buf, ref segment_table[0].cache[nbuf].buf, e_key, 0);
}
else
{
segment_table[0].cache[nbuf].buf = pd[i].fs.ReadBytes(addr + DEFS.SYSTEM_USED_PAGE_SPACE, (int)page_size);
}
if (old_crc != 0)
{
uint new_crc = VSCRC32.CountCrc(segment_table[0].cache[nbuf].buf);
if (old_crc != new_crc)
{
throw new VSException(DEFS.E0033_INVALID_CRC_CODE, "Space: " + DESCRIPTOR.name + ", Page#: " + n.ToString());
}
}
PGRead++;
// Update page table entry by but# ans sett 'read' state
segment_table[sg].page_table[pg].page_state = DEFS.PAGE_READ;
segment_table[sg].page_table[pg].bufno = nbuf;
// Update cache entry by page#
segment_table[0].cache[nbuf].page_no = n;
}
}
}
