User talk:Timeslip

BSA hashes

Oblivions BSA hashing algorithm is different from morrowinds, and doesn't appear to be documented anywhere. In case anyone else is working on any BSA tools and wants the algorithm, I'll post the C# code that obmm uses here.

//file is the file name without the extension
//Extension is the extension of a file, including the preceding '.'
//For hashing anything other than file names, ext must be an empty string
public static ulong GenHash(string file, string ext) {
  file=file.ToLower();
  ext=ext.ToLower();
  ulong hash=0;
  if(file.Length>0) {
    hash=(ulong)(
      (((byte)file[file.Length-1])*0x1)+
      ((file.Length>2?(byte)file[file.Length-2]:(byte)0)*0x100)+
      (file.Length*0x10000)+
      (((byte)file[0])*0x1000000)
    );
  }
  if(file.Length>3) {
    hash+=(ulong)(GenHash2(file.Substring(1, file.Length-3))*0x100000000);
  }
  if(ext.Length>0) {
    hash+=(ulong)(GenHash2(ext)*0x100000000);
    byte i=0;
    switch(ext) {
      case ".nif": i=1; break;
      case ".kf": i=2; break;
      case ".dds": i=3; break;
      case ".wav": i=4; break;
    }
    if(i!=0) {
      byte a=(byte)(((i&0xfc)<<5)+(byte)((hash&0xff000000)>>24));
      byte b=(byte)(((i&0xfe)<<6)+(byte)(hash&0xff));
      byte c=(byte)((i<<7)+(byte)((hash&0xff00)>>8));
      hash-=hash&0xFF00FFFF;
      hash+=(uint)((a<<24)+b+(c<<8));
    }
  }
  return hash;
}

private static uint GenHash2(string s) {
  uint hash=0;
  for(int i=0;i<s.Length;i++) {
    hash*=0x1003f;
    hash+=(byte)s[i];
  }
  return hash;
}

This may not be 100% accurate, but I've run it over every file and folder in oblivion v1.1's meshes, textures and misc BSAs without any mismatches, so I'm fairly sure it's right.