Need Comments on this method?

ritchie · Joined: 13 Sep 2003 Posts: 87

Hi,

I have an application in a security system wherein I use a 2byte (16bit) data.

This 16bit corresponds to a door access wherein each bit corresponds to one door. If it is 1 u are granted access to that door otherwise if 0 no access.

What wud be a good algorithm or a snippet to read every bit of the 16bit such that we can distinguish which door are granted for a specific IDs.

Thank u.

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

I'm not sure if I understand you problem correctly, but you can use the CCS function bit_test() for checking the bits of a variable:

Al · Joined: 13 Nov 2003 Posts: 28 Location: Belfast

Hi Ritchie,
My understanding is that you would require a 16bit word to be stored for every user. You could manitain a 2-D array for this.

int16 securityDatabase[NUMBEROFUSERS][2]

This will give you a table with 2 columns - the first a 16 bit UserID and the second a the security map for that user to all the doors.

Unfortunately you would have to loop through and test each bit using the above bit test - incrementing which bit you are testing for each iteration of the loop.

I hope this helps.
_________________
Alan Murray

j11 · Guest

why not make each persons code the correct 16 bit number for the doors that thay have access too. if a person has acces to all doors his code would be 65535. you could use some type of encryption scheme to make it less obvious.

Al · Joined: 13 Nov 2003 Posts: 28 Location: Belfast

SteveS · Joined: 27 Oct 2003 Posts: 126

J11's idea IS a bit -map. Say you want access to doors 2 & 3 (and assume the 'first' door is #1 not #0). That persons 'code' would be (8 bit binary) 0000 0110. Yes, that = 5 but door five would be 0001 0000. One bit is set for each door and is 2^(door#-1).

- SteveS

ritchie · Joined: 13 Sep 2003 Posts: 87