Best way to generate order numbers for an online store?

Question

Every order in my online store has a user-facing order number. I\'m wondering the best way to generate them. Criteria include:

• Short
• Easy to say over the

Answer 1

Here is an implementation for a system I proposed in an earlier question:

MAGIC = [];
29.downto(0) {|i| MAGIC << 839712541[i]}

def convert(num)
  order = 0
  0.upto(MAGIC.length - 1)  {|i| order = order << 1 | (num[i] ^ MAGIC[i]) }
  order
end

It's just a cheap hash function, but it makes it difficult for an average user to determine how many orders have been processed, or a number for another order. It won't run out of space until you've done 2³⁰ orders, which you won't hit any time soon.

Here are the results of convert(x) for 1 through 10:

1:  302841629
2:  571277085
3:   34406173
4:  973930269
5:  437059357
6:  705494813
7:  168623901
8:  906821405
9:  369950493
10: 638385949