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authorSverker Eriksson <[email protected]>2011-10-18 16:05:14 +0200
committerSverker Eriksson <[email protected]>2011-10-18 16:12:00 +0200
commit852827dab8fa74167f9a000998304e3961010797 (patch)
treef593dfab5b0b8d33efffec2cd8945c44cc9f4a20 /lib
parent0bff7dcedcb793f1d4d016ecee893964c790ded1 (diff)
parentb52a2170d13fe7ff6e4e3b146b63d8f68c2aaadf (diff)
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Merge branch 'sverker/random-improved-algo'
* sverker/random-improved-algo: Improve algorithm in module random. Fix a bug in the implementation of the pseudo-random number generator OTP-8713
Diffstat (limited to 'lib')
-rw-r--r--lib/stdlib/doc/src/random.xml5
-rw-r--r--lib/stdlib/src/random.erl42
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}