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authorSverker Eriksson <[email protected]>2011-03-28 16:38:57 +0200
committerSverker Eriksson <[email protected]>2011-03-28 19:08:49 +0200
commitb52a2170d13fe7ff6e4e3b146b63d8f68c2aaadf (patch)
tree65e17f5ad014584b327ac49dcf47e37f05f87d4b /lib/stdlib/src/random.erl
parentc50f179a15ad8c8bcbc7a71101a9ca23f19f6e8f (diff)
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Improve algorithm in module random.
Avoid seed values that are even divisors of the primes and by that prevent getting seeds that are stuck on zero. Example: random:seed(0,0,0) would produce a series of only zeros.
Diffstat (limited to 'lib/stdlib/src/random.erl')
-rw-r--r--lib/stdlib/src/random.erl44
1 files changed, 25 insertions, 19 deletions
diff --git a/lib/stdlib/src/random.erl b/lib/stdlib/src/random.erl
index d94722cb33..606edbb1fb 100644
--- a/lib/stdlib/src/random.erl
+++ b/lib/stdlib/src/random.erl
@@ -1,7 +1,7 @@
%%
%% %CopyrightBegin%
%%
-%% Copyright Ericsson AB 1996-2009. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2011. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
@@ -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
@@ -60,17 +68,15 @@ seed({A1, A2, A3}) ->
-spec seed(integer(), integer(), integer()) -> 'undefined' | ran().
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.
@@ -82,11 +88,11 @@ 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 = B1/30269 + B2/30307 + B3/30323,
+ R = B1/?PRIME1 + B2/?PRIME2 + B3/?PRIME3,
R - trunc(R).
%% uniform(N) -> I
@@ -107,10 +113,10 @@ uniform(N) when is_integer(N), N >= 1 ->
-spec uniform_s(ran()) -> {float(), ran()}.
uniform_s({A1, A2, A3}) ->
- B1 = (A1*171) rem 30269,
- B2 = (A2*172) rem 30307,
- B3 = (A3*170) rem 30323,
- R = B1/30269 + B2/30307 + B3/30323,
+ 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}