The R13B03 release.OTP_R13B03

1 files changed, 124 insertions, 0 deletions

diff --git a/lib/stdlib/src/random.erl b/lib/stdlib/src/random.erl
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+%%
+%% %CopyrightBegin%
+%% 
+%% Copyright Ericsson AB 1996-2009. 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
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved online at http://www.erlang.org/.
+%% 
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and limitations
+%% under the License.
+%% 
+%% %CopyrightEnd%
+%%
+-module(random).
+
+%% Reasonable random number generator.
+%%  The method is attributed to B. A. Wichmann and I. D. Hill
+%%  See "An efficient and portable pseudo-random number generator",
+%%  Journal of Applied Statistics. AS183. 1982. Also Byte March 1987.
+
+-export([seed/0, seed/1, seed/3, uniform/0, uniform/1,
+	 uniform_s/1, uniform_s/2, seed0/0]).
+
+%%-----------------------------------------------------------------------
+%% The type of the state
+
+-type ran() :: {integer(), integer(), integer()}.
+
+%%-----------------------------------------------------------------------
+
+-spec seed0() -> ran().
+
+seed0() ->
+    {3172, 9814, 20125}.
+
+%% seed()
+%%  Seed random number generation with default values
+
+-spec seed() -> ran().
+
+seed() ->
+    reseed(seed0()).
+
+%% seed({A1, A2, A3}) 
+%%  Seed random number generation 
+
+-spec seed({integer(), integer(), integer()}) -> 'undefined' | ran().
+
+seed({A1, A2, A3}) ->
+    seed(A1, A2, A3).
+
+%% seed(A1, A2, A3) 
+%%  Seed random number generation 
+
+-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}).
+
+
+-spec reseed(ran()) -> ran().
+
+reseed({A1, A2, A3}) ->
+    case seed(A1, A2, A3) of
+	undefined -> seed0();
+	{_,_,_} = Tuple -> Tuple
+    end.	
+
+%% uniform()
+%%  Returns a random float between 0 and 1.
+
+-spec uniform() -> float().
+
+uniform() ->
+    {A1, A2, A3} = case get(random_seed) of
+		       undefined -> seed0();
+		       Tuple -> Tuple
+		   end,
+    B1 = (A1*171) rem 30269,
+    B2 = (A2*172) rem 30307,
+    B3 = (A3*170) rem 30323,
+    put(random_seed, {B1,B2,B3}),
+    R = A1/30269 + A2/30307 + A3/30323,
+    R - trunc(R).
+
+%% uniform(N) -> I
+%%  Given an integer N >= 1, uniform(N) returns a random integer
+%%  between 1 and N.
+
+-spec uniform(pos_integer()) -> pos_integer().
+
+uniform(N) when is_integer(N), N >= 1 ->
+    trunc(uniform() * N) + 1.
+
+
+%%% Functional versions
+
+%% uniform_s(State) -> {F, NewState}
+%%  Returns a random float between 0 and 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 = A1/30269 + A2/30307 + A3/30323,
+    {R - trunc(R), {B1,B2,B3}}.
+
+%% uniform_s(N, State) -> {I, NewState}
+%%  Given an integer N >= 1, uniform(N) returns a random integer
+%%  between 1 and N.
+
+-spec uniform_s(pos_integer(), ran()) -> {integer(), ran()}.
+
+uniform_s(N, State0) when is_integer(N), N >= 1 ->
+    {F, State1} = uniform_s(State0),
+    {trunc(F * N) + 1, State1}.