Update Trigger and COLUMNS_UPDATED()

Question

Let me rephrase my question:
I want to know if there is a faster way (probably using bit operators) to see if COLUMNS_UPDATED() in an update trigger on a table with more than 8 columns contains any column other than 1 specific column I will refer
to as 'columnToIgnore'. I don't care about which columns are included or if the value has actually changed, only that there are other columns present.
Original question:
I have inherited a Sql Server database + schema and corresponding application and I have been tasked with speeding up the batch update of users in the database. After running some profiling I discovered that the reason it was slow is because of an update
trigger on the users table. I did some “cleaning up” of the trigger and now it runs faster but I still think it could be more efficient. The objective of the trigger is to write to an Audit table any time an update takes place and any column is updated (it
does not actually matter if the value has changed or not) with the exception of 1 specific column. Now I have the following code in the trigger which I had refactored from something much uglier.
DECLARE @ColumnsUpdated VARBINARY(100)
SET @ColumnsUpdated = COLUMNS_UPDATED()
DECLARE @onlyIgnoreColumnChanged int
SET @onlyIgnoreColumnChanged = 1
SET @onlyIgnoreColumnChanged = 1
IF (EXISTS(SELECT 1
FROM INFORMATION_SCHEMA.COLUMNS Field
WHERE TABLE_NAME = 'users'
AND sys.fn_IsBitSetInBitmask(@ColumnsUpdated, COLUMNPROPERTY(OBJECT_ID('dbo.users'), COLUMN_NAME, 'ColumnID')) <> 0
AND column_name !='columnToIgnore')) BEGIN
SET @onlyIgnoreColumnChanged = 0
END
Ideally I would change the code to disable the trigger and do the insert myself BUT the code is old Classic ASP ( ie. VBScript with ODBC database connections) so I am not going to change any of the calling code because that would cost too much time and probably
create more problems than I am solving.
My proposed fix which I am unsure of how to code in SQL:
It seems to me that there should be a way to get the proper id or position for the column and see if the column was used in the COLUMNS_UPDATED().
If it was not used then we can set @onlynieuwchanged to 0 for the remaining code (not shown)
If it was used then remove the bit from the COLUMNS_UPDATED() and see if it is empty
If its empty then then we can set @onlynieuwchanged to 1 for the remaining code (not shown)
If it’s not empty then then we can set @onlynieuwchanged to 0 for the remaining code (not shown)
My problem is I am not sure how to go about coding this logic in SQL. I would think it would be possible with BIT operators? It would seem this could be more efficient than what I have now as it would get rid of the select statement which could slow down
a large batch update.
Notes
My table has 30+ some columns so more than 8 which is relevant when working with COLUMNS_UPDATED() from what I have read. It also means that testing each column with UPDATE() would probably be more inefficient than what I have now.
The update is called from the front end code (VBScript) which currently times out although not as much as it used to with my latest change. I cannot alter the code to run async mode and show progress, it would be easier for me to update the trigger.
Reason for audit - we only record the user id in an audit table. This is then used to force a sync to another system outside of our source control that is used for various other tasks (mailings, views, etc). Again, I do not want to change how this system
works, I only want to speed up the existing trigger with minimal effort.
Sql Server version 2012, database Schema is set to Sql server 2005 compatibility mode.
Any help would be greatly appreciated. Thank you in advance!
-Igor

Answer 1

Thank you again everyone for your input. As I mentioned there is much out of my control. This is an active application worked on by many developers and has been pieced together over the past 10+ years. It is NOT well written, the database schema has MUCH
to be desired, and the code is the classic definition of 'spaghetti' code and multiple platforms are used to access the data, and there are millions of lines of code. There is nothing I can do about all of this which is why I am ignoring much of the advice.
Sure, if this was a new application or something that was well written and possible to do some modifications then I would BUT it's not. If I was given 1 year of dedicated time to fix everything... well, I would probably throw it all away and start from scratch.
Here is what I finally came up with. It is probably not  much faster, if at all, but when I started this I thought there would be a simple solution that I did not see. I will probably leave my code the way it was but will include the following for reference.
DECLARE @bit int, @field int, @char int, @comparisonField VARBINARY(100)
-- the following segment recreates the value contained in COLUMNS_UPDATED() if only the field nieuw was altered and stores that value in field @comparisonField
SET @field = (SELECT COLUMNPROPERTY(OBJECT_ID('dbo.users'), 'columnToIgnore', 'ColumnID')) -- geth the field id for column nieuw
select @bit = (@field - 1 )% 8 + 1
select @bit = power(2,@bit - 1)
select @char = ((@field - 1) / 8) + 1
-- select @field AS [Field number], @char AS [Char], @bit AS [Bit] -- debug code to check the bits that are tested.
-- Recreate the binary value of just having the field present in the columns_updated
SELECT @comparisonField = CONVERT(VARBINARY(100),'0x' + RIGHT('000000000000000000' + RIGHT(CONVERT(VARCHAR(30), CONVERT(varbinary(1), @bit), 1), 2), @char*2), 1)
-- if the generated value in @comparisonField is the same as COLUMNS_UPDATED() then only nieuw was updated
IF @comparisonField <> COLUMNS_UPDATED() BEGIN
-- code to add to the tracking table
END
-Igor