Excel reserved file sharing hash function (C#)

excel_shared_workbook_hash.cs

/*
This computes the 16-bit hash used to protect Excel workbooks through most versions.

When trying to open such a sheet for editing, you'll get a message such as:
    blah.xlsx is reserved by [user]. Enter password for write access, or open read only.

In xl\workbook.xml the hash is stored as follows: <fileSharing userName="user" reservationPassword="ABCD" />
In that case, you'd compare the output of the hash function to 0xABCD.

For 99% of cases you can just throw a wordlist like rockyou at any hash and it'll spit out hundreds of collisions.
*/

ushort Hash(string password)
{
	if (password.Length > 15)
	{
		return 0;
	}
	ushort hash = 0;
	byte[] pb = Encoding.ASCII.GetBytes(password);
	for (int i = pb.Length - 1; i >= 0; i--)
	{
		byte pch = pb[i];
		hash = (ushort)(((hash >> 14) & 0x01) | ((hash << 1) & 0x7fff));
		hash ^= pch;
	}
	hash = (ushort)(((wPasswordHash >> 14) & 0x01) | ((hash << 1) & 0x7fff));
	hash ^= (0x8000 | ('N' << 8) | 'K');
	hash ^= (ushort)hash.Length;
	return hash;
}