Re: Generating random unique alphanumeric IDs

On Mon, 17 Aug 2009 12:37:33 +0200
"Daniel Verite" <daniel(at)manitou-mail(dot)org> wrote:

> http://archives.postgresql.org/pgsql-general/2009-07/msg00194.php

As an exercise I wrote the decrypt version

create or replace function feistel_encrypt(value int)
returns int as
$$
declare
l1 int;
l2 int;
r1 int;
r2 int;
i int:=0;
begin
l1:= (value >> 16) & 65535;
r1:= value & 65535;
while i<3 loop
l2:=r1;
r2:=l1 # ((((1366.0 *
r1+150889)%714025)/714025.0)*32767)::int;
l1:=l2;
r1:=r2;
i:=i+1;
end loop;
return ((l1::bigint<<16) + r1);
end;
$$ language plpgsql strict immutable;
create or replace function feistel_decrypt(value int)
returns int as
$$
declare
l1 int;
l2 int;
r1 int;
r2 int;
i int:=0;
begin
l2:= (value >> 16) & 65535;
r2:= value & 65535;
while i<3 loop
r1=l2;
l1:=r2#((((1366.0*l2+150889)%714025)/714025.0)*32767)::int;
l2:=l1;
r2:=r1;
i:=i+1;
end loop;
return ((l2::bigint<<16) + r2);
end;
$$ language plpgsql strict immutable;

so that

10 = feistel_decrypt(feistel_encrypt(10))

Since I'm then converting to_hex to shorten the string I was
thinking to add some more bits of randomness since eg.

to_hex(10) = 'a'

In the line of
select lpad(
to_hex(feistel_encrypt(10)),7 , to_hex((rand()*2^31)::int)
);

I was wondering if there is any better way to get alphanumeric
random string quickly. Since uniqueness is assured by passing a
sequence to fesitel_encrypt, I just need turning into to
alphanumeric quickly.

--
Ivan Sergio Borgonovo
http://www.webthatworks.it