One-to-one integer mapping function

Question

We are using MySQL and developing an application where we\'d like the ID sequence not to be publicly visible... the IDs are hardly top secret and there is no significant iss

Answer 1

Do what Henrik said in his second suggestion. But since these values seem to be used by people (else you wouldn't want to randomize them). Take one additional step. Multiply the sequential number by a large prime and reduce mod N where N is a power of 2. But choose N to be 2 bits smaller than you can store. Next, multiply the result by 11 and use that. So we have:

Hash = ((count * large_prime) % 536870912) * 11

The multiplication by 11 protects against most data entry errors - if any digit is typed wrong, the result will not be a multiple of 11. If any 2 digits are transposed, the result will not be a multiple of 11. So as a preliminary check of any value entered, you check if it's divisible by 11 before even looking in the database.