Is there a faster way to check holidays NETWORKDAYS() replacement

I wrote this routine for a spreadsheet I am working on, but I'm not sure that its the fastest way, it emulates networkdays exactly, but since i cant guarantee that function will be available I wrote this function.

I was wondering if anybody had any ideas on speeding up the holiday checking, while maintaining compatibility with the networkdays function.

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The problem is chips array formula isnt compatible with NETWORKDAYS

:-
My code returns the same as networkdays except for the following senarios, which I assume is due to the difference in visual basic's handling of dates in 1900

Start-------End----------Network Days--WorkingDays------Chips array
18/04/2009 -08/05/2009------13-----------13---------------13
08/05/2009 18/04/2009 -----[-13]--------[-13]--------------#N/A
29/02/1900 08/04/2064-----42813------ 42813----------- 42813
08/04/2064 29/02/1900 ---[-42813]----[-42813]------------#N/A
00/01/1900 00/01/1900 ------0---------- 0------------#N/A
06/01/1900 20/01/1900------11------------11---------------11
00/01/1900 00/01/1900------ 0-------------0-----------------#N/A
01/01/1900 01/01/1900------ 0------------[-5]----------------- 0
02/01/1900 02/01/1900-------1------------1----------------0
03/01/1900 03/01/1900-------1------------1-----------------1
29/02/1900 29/03/1900 ------22-----------22----------------22
01/01/1900 03/01/1900-------2-----------[-3]---------------1
[BLANK ] [blank ]-------0------------0--------------#N/A
Fred--------03/01/1900------#VALUE!---#VALUE!---------#N/A
999999999 999999999 --------#NUM!-----#VALUE!----------1

after ironing out some bugs :-

I tested it against network days and in all the cases I could come up with it returns the same values, I just cant help thinking that the holidays could be optimized since it would have to scan the whole list of a range even if most of it was blank! (i tried it with holiday list =$b:$b, it took 4.5 seconds as against networkdays 0.7 seconds)(1m items in holiday list))

any ideas on speeding up, without loosing compatibility with NETWORKDAYS?

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