private bool VerifyFileChecksum(byte[] Image, UInt32 Offset)
{
// This function only checks fixed checksum-values 0x55 and 0xAA.
UInt16 FileHeaderSize = 0x18;
UInt32 FileSize = ByteOperations.ReadUInt24(Image, Offset + 0x14);
byte[] Header = new byte[FileHeaderSize - 1];
System.Buffer.BlockCopy(Image, (int)Offset, Header, 0, FileHeaderSize - 1);
ByteOperations.WriteUInt16(Header, 0x10, 0); // Clear checksum
byte CurrentHeaderChecksum = ByteOperations.ReadUInt8(Image, Offset + 0x10);
byte CalculatedHeaderChecksum = ByteOperations.CalculateChecksum8(Header, 0, (UInt32)FileHeaderSize - 1);
if (CurrentHeaderChecksum != CalculatedHeaderChecksum)
{
return(false);
}
byte FileAttribs = ByteOperations.ReadUInt8(Image, Offset + 0x13);
byte CurrentFileChecksum = ByteOperations.ReadUInt8(Image, Offset + 0x11);
if ((FileAttribs & 0x40) > 0)
{
// Calculate file checksum
byte CalculatedFileChecksum = ByteOperations.CalculateChecksum8(Image, Offset + FileHeaderSize, FileSize - FileHeaderSize);
if (CurrentFileChecksum != CalculatedFileChecksum)
{
return(false);
}
}
else
{
// Fixed file checksum
if ((CurrentFileChecksum != 0xAA) && (CurrentFileChecksum != 0x55))
{
return(false);
}
}
return(true);
}
private void CalculateFileChecksum(byte[] Image, UInt32 Offset)
{
UInt16 FileHeaderSize = 0x18;
UInt32 FileSize = ByteOperations.ReadUInt24(Image, Offset + 0x14);
ByteOperations.WriteUInt16(Image, Offset + 0x10, 0); // Clear checksum
byte NewChecksum = ByteOperations.CalculateChecksum8(Image, Offset, (UInt32)FileHeaderSize - 1);
ByteOperations.WriteUInt8(Image, Offset + 0x10, NewChecksum); // File-Header checksum
byte FileAttribs = ByteOperations.ReadUInt8(Image, Offset + 0x13);
if ((FileAttribs & 0x40) > 0)
{
// Calculate file checksum
byte CalculatedFileChecksum = ByteOperations.CalculateChecksum8(Image, Offset + FileHeaderSize, FileSize - FileHeaderSize);
ByteOperations.WriteUInt8(Image, Offset + 0x11, CalculatedFileChecksum);
}
else
{
// Fixed file checksum
ByteOperations.WriteUInt8(Image, Offset + 0x11, 0xAA);
}
}