Update quickrand.

CloudI · Sep 5, 2017 · f673323 · f673323
1 parent f1e73be
commit f673323
Show file tree

Hide file tree

Showing 5 changed files with 38 additions and 17 deletions.
diff --git a/src/ChangeLog b/src/ChangeLog
@@ -1,6 +1,10 @@
 # -*- coding: utf-8; tab-width: 4; -*-
 # ex: set fenc=utf-8 sts=4 ts=4 et nomod:
 
+2017-09-04 Michael Truog   <mjtruog [at] gmail (dot) com>
+
+    * Update quickrand
+
 2017-09-02 Michael Truog   <mjtruog [at] gmail (dot) com>
 
     * Fix the service configuration option response_timeout_immediate_max

diff --git a/src/lib/README.markdown b/src/lib/README.markdown
@@ -64,8 +64,8 @@ as external dependencies within CloudI (i.e., with a `cloudi_x_` prefix).
 `Quick Erlang Random Number Generation`
 
 - `https://github.com/okeuday/quickrand`
-- `commit de0f2c7657723a223c5f8fc92a388e101697eae3 (v1.7.1)`
-- `Wed Jun  7 15:51:52 PDT 2017`
+- `commit 6072555ae3269a6a807002ad59b78efbb0104b28`
+- `Mon Sep  4 19:29:44 PDT 2017`
 - `MIT`
 
 `reltool_util`

diff --git a/src/lib/quickrand/src/quickrand.erl b/src/lib/quickrand/src/quickrand.erl
@@ -306,9 +306,14 @@ strong_uniform_range(Min, Max)
 strong_float() ->
     % 53 bits maximum for double precision floating point representation
     % (need to use a maximum value of math:pow(2, 53) with extra bit,
-    %  i.e. 16#1fffffffffffff + 1)
-    <<I:53/unsigned-integer, Bit:1, _:2>> = crypto:strong_rand_bytes(7),
-    (I + Bit) * ?DBL_EPSILON_DIV2.
+    %  i.e. 1 + 16#1fffffffffffff)
+    <<Bit:1, I:53/unsigned-integer, _:2>> = crypto:strong_rand_bytes(7),
+    if
+        Bit == 1, I == 0 ->
+            1.0;
+        true ->
+            I * ?DBL_EPSILON_DIV2
+    end.
 
 %%-------------------------------------------------------------------------
 %% @doc
@@ -338,7 +343,9 @@ strong_floatM() ->
     <<I:53/unsigned-integer, _:3>> = crypto:strong_rand_bytes(7),
     if
         I == 0 ->
-            ?DBL_EPSILON_DIV2;
+            % almost never executes this case, an additional function call
+            % is necessary to have a uniform distribution
+            strong_floatM();
         true ->
             I * ?DBL_EPSILON_DIV2
     end.

diff --git a/src/lib/quickrand/src/quickrand_cache.erl b/src/lib/quickrand/src/quickrand_cache.erl
@@ -81,8 +81,13 @@
     float().
 
 float() ->
-    <<I:53/unsigned-integer, Bit:1, _:2>> = rand_bytes(7),
-    (I + Bit) * ?DBL_EPSILON_DIV2.
+    <<Bit:1, I:53/unsigned-integer, _:2>> = rand_bytes(7),
+    if
+        Bit == 1, I == 0 ->
+            1.0;
+        true ->
+            I * ?DBL_EPSILON_DIV2
+    end.
 
 %%-------------------------------------------------------------------------
 %% @doc
@@ -94,8 +99,14 @@ float() ->
     {float(), state()}.
 
 float(State) ->
-    {<<I:53/unsigned-integer, Bit:1, _:2>>, NewState} = rand_bytes(7, State),
-    {(I + Bit) * ?DBL_EPSILON_DIV2, NewState}.
+    {<<Bit:1, I:53/unsigned-integer, _:2>>, NewState} = rand_bytes(7, State),
+    Value = if
+        Bit == 1, I == 0 ->
+            1.0;
+        true ->
+            I * ?DBL_EPSILON_DIV2
+    end,
+    {Value, NewState}.
 
 %%-------------------------------------------------------------------------
 %% @doc
@@ -136,7 +147,7 @@ floatM() ->
     <<I:53/unsigned-integer, _:3>> = rand_bytes(7),
     if
         I == 0 ->
-            ?DBL_EPSILON_DIV2;
+            floatM();
         true ->
             I * ?DBL_EPSILON_DIV2
     end.
@@ -152,13 +163,12 @@ floatM() ->
 
 floatM(State) ->
     {<<I:53/unsigned-integer, _:3>>, NewState} = rand_bytes(7, State),
-    Value = if
+    if
         I == 0 ->
-            ?DBL_EPSILON_DIV2;
+            floatM(NewState);
         true ->
-            I * ?DBL_EPSILON_DIV2
-    end,
-    {Value, NewState}.
+            {I * ?DBL_EPSILON_DIV2, NewState}
+    end.
 
 %%-------------------------------------------------------------------------
 %% @doc

diff --git a/src/lib/quickrand/src/quickrand_internal.hrl b/src/lib/quickrand/src/quickrand_internal.hrl
@@ -29,7 +29,7 @@
 
 -define(APPLICATION, quickrand).
 
-% 1 / (16#1fffffffffffff + 1) =:= math:pow(2, -53) to provide [0.0 .. 1.0]
+% 1 / (1 + 16#1fffffffffffff) =:= math:pow(2, -53) to provide [0.0 .. 1.0]
 -define(DBL_EPSILON_DIV2, 1.1102230246251565e-16).
 
 -define(BYTES_RESOLUTION, 4). % bytes