diff options
| -rw-r--r-- | lib/stdlib/doc/src/random.xml | 5 | ||||
| -rw-r--r-- | lib/stdlib/src/random.erl | 42 |
2 files changed, 29 insertions, 18 deletions
diff --git a/lib/stdlib/doc/src/random.xml b/lib/stdlib/doc/src/random.xml index 93affc3191..1b8fa44883 100644 --- a/lib/stdlib/doc/src/random.xml +++ b/lib/stdlib/doc/src/random.xml @@ -136,6 +136,11 @@ <c>random_seed</c> to remember the current seed.</p> <p>If a process calls <c>uniform/0</c> or <c>uniform/1</c> without setting a seed first, <c>seed/0</c> is called automatically.</p> + <p>The implementation changed in R15. Upgrading to R15 will break + applications that expect a specific output for a given seed. The output + is still deterministic number series, but different compared to releases + older than R15. The seed <c>{0,0,0}</c> will for example no longer + produce a flawed series of only zeros.</p> </section> </erlref> diff --git a/lib/stdlib/src/random.erl b/lib/stdlib/src/random.erl index dbb524cc74..d7b51a151c 100644 --- a/lib/stdlib/src/random.erl +++ b/lib/stdlib/src/random.erl @@ -26,6 +26,10 @@ -export([seed/0, seed/1, seed/3, uniform/0, uniform/1, uniform_s/1, uniform_s/2, seed0/0]). +-define(PRIME1, 30269). +-define(PRIME2, 30307). +-define(PRIME3, 30323). + %%----------------------------------------------------------------------- %% The type of the state @@ -44,7 +48,11 @@ seed0() -> -spec seed() -> ran(). seed() -> - reseed(seed0()). + case seed_put(seed0()) of + undefined -> seed0(); + {_,_,_} = Tuple -> Tuple + end. + %% seed({A1, A2, A3}) %% Seed random number generation @@ -66,17 +74,15 @@ seed({A1, A2, A3}) -> A3 :: integer(). seed(A1, A2, A3) -> - put(random_seed, - {abs(A1) rem 30269, abs(A2) rem 30307, abs(A3) rem 30323}). + seed_put({(abs(A1) rem (?PRIME1-1)) + 1, % Avoid seed numbers that are + (abs(A2) rem (?PRIME2-1)) + 1, % even divisors of the + (abs(A3) rem (?PRIME3-1)) + 1}). % corresponding primes. --spec reseed(ran()) -> ran(). - -reseed({A1, A2, A3}) -> - case seed(A1, A2, A3) of - undefined -> seed0(); - {_,_,_} = Tuple -> Tuple - end. +-spec seed_put(ran()) -> 'undefined' | ran(). + +seed_put(Seed) -> + put(random_seed, Seed). %% uniform() %% Returns a random float between 0 and 1. @@ -88,11 +94,11 @@ uniform() -> undefined -> seed0(); Tuple -> Tuple end, - B1 = (A1*171) rem 30269, - B2 = (A2*172) rem 30307, - B3 = (A3*170) rem 30323, + B1 = (A1*171) rem ?PRIME1, + B2 = (A2*172) rem ?PRIME2, + B3 = (A3*170) rem ?PRIME3, put(random_seed, {B1,B2,B3}), - R = A1/30269 + A2/30307 + A3/30323, + R = B1/?PRIME1 + B2/?PRIME2 + B3/?PRIME3, R - trunc(R). %% uniform(N) -> I @@ -116,10 +122,10 @@ uniform(N) when is_integer(N), N >= 1 -> State1 :: ran(). uniform_s({A1, A2, A3}) -> - B1 = (A1*171) rem 30269, - B2 = (A2*172) rem 30307, - B3 = (A3*170) rem 30323, - R = A1/30269 + A2/30307 + A3/30323, + B1 = (A1*171) rem ?PRIME1, + B2 = (A2*172) rem ?PRIME2, + B3 = (A3*170) rem ?PRIME3, + R = B1/?PRIME1 + B2/?PRIME2 + B3/?PRIME3, {R - trunc(R), {B1,B2,B3}}. %% uniform_s(N, State) -> {I, NewState} |