Hi. I have a compilation error:

_build/default/lib/quickrand/src/quickrand_hash.erl:80: unknown dialyzer warning option: no_underspecs

I have Erlang/OTP 24 and Dialyzer version v4.3 but the argument no_underspecs has been supported since version 4.4.

1> erlang:system_info(otp_release).
"24"
...
$> dialyzer --version
Dialyzer version v4.3

Hello!

It looks like quickrand:seed/0 doesn't work on OTP versions less than 20.

This is because quickrand:seed_rand/3 attempts to call rand:seed/2 using the exsp parameter that is not defined in OTP < 20. (This is src/quickrand.erl:373)

There is an ifdef in place to try and catch this situation, but it's currently short-circuited to true. Perhaps a commit got lost somewhere along the way?

Hi Michael

Is there any downside to cache the state within quickrand_cache:init/1 in a global cache?

_ = erlang:put(?TUPLE_PDICT_KEY, state_to_tuple(new(Options))),

Something along these lines quickrand_cache:init_/1:

-spec init_(Options :: options()) ->
    ok.
init_(Options) ->
    persistent_term:put(?TUPLE_PDICT_KEY, state_to_tuple(new(Options))).

Then, add this new quickrand_cache:rand_bytes_/1:

-spec rand_bytes_(N :: pos_integer()) ->
    binary().

rand_bytes_(N)
    when is_integer(N), N > 0 ->
    {I, CacheSize, Cache} = persistent_term:get(?TUPLE_PDICT_KEY),
    {Bytes, NewI, NewCache} = bytes_get(N, I, CacheSize, Cache),
    %% !!! don't know what can be done here as persistent_term:put/2 is really slow (triggers GC) !!!
    ok = persistent_term:put(?TUPLE_PDICT_KEY, {NewI, CacheSize, NewCache}),
    Bytes.

My application is heavily using your uuid module to generate v4 UUIDs.
While checking your code today i realized that you've added a nice caching layer to it.

I'm generating about 10 million v4 UUIDs per day and would like to switch to uuid:get_v4(cached_):

get_v4(cached) ->
    <<Rand1:48, _:4, Rand2:12, _:2, Rand3:62>> =
        quickrand_cache:rand_bytes_(16),
    <<Rand1:48,
      0:1, 1:1, 0:1, 0:1,  % version 4 bits
      Rand2:12,
      1:1, 0:1,            % RFC 4122 variant bits
      Rand3:62>>;

With this in place, all my processes will use the same cached state and will avoid to store extra data in their process dictionnary:

ok = quickrand_cache:init_([{cache_size, 16}]),
[...]
V4 = uuid:get_v4(cached),

Any issue with this?

Thanks.

src/quickrand.erl:89: crypto:rand_bytes/1 is deprecated and will be removed in in a future release; use crypto:strong_rand_bytes/1