Hi everyone,
I am working on an embedded linux project that requires me to generate a unique 4 digit code based on my device id. My device ID could go from 1 - 1024. Is there a simple mathametical formula that I could use to generate the required number. I try to write something on my own and I am not successful at generating unique numbers.
Any help is much appericiated! Thanks everyone!
EZ
If device IDs are not unique, how to expect to generate unique numbers based on them? If device IDs are unique, then just use the device ID.
-- Grant Edwards grante@visi.com
Sorry, I didn't explain myself well here. The device ID's are unique. Treat these generated numbers as passwords & we don't want to make it obvious .
EZ
expect to generate unique
lookup "hash functions"
9999 is 10011100001111 -> 14 bits
so insert four constant bits in 4 arbitrary bit positions. e.g.
x = id-1; x0 = x & 0x0003; // bits 1, 0 x1 = (x & 0x001C)
evensimpler: strtching:
(id*9999)/1024
-Michael
...or just (id+3).
:)
We've lost the OP's desire that it not be a simple relationship.
I like the bit-insertion technique.
You can even shuffle the bits around a bit.
And for the inserted bits, don't used constants, but another bit already in the id. You are going to drop those bits to "decode" it anyway.
4 digits? I suppose 0-8191 is acceptible (2^13) or better, (1000-9191) so they are no leading zeros in the passkey.and 1-1024 (0-1023) is (2^10)
// // just make sure you include every bit 0-9 at least // once in the array //
char bitshuffle[13] = {0,2,4,6,8,1,3,5,7,9,1,2,3);
int gencode(int id) { int code = 0; for (int i=0; i
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