From f4c65597ea7b1c148b0b45ca3cf09c4ab76dd39a Mon Sep 17 00:00:00 2001
From: Martin Sumner <martin.sumner@adaptip.co.uk>
Date: Wed, 24 Oct 2018 15:42:21 +0100
Subject: [PATCH] log 2 compat

Need to support math:log2 in early versions of OTP (for Riak)
---
 rebar.config           |  2 ++
 src/leveled_math.erl   | 38 ++++++++++++++++++++++++++++++++++++++
 src/leveled_tictac.erl |  2 +-
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 src/leveled_math.erl

diff --git a/rebar.config b/rebar.config
index 7a46b31..a6c6659 100644
--- a/rebar.config
+++ b/rebar.config
@@ -1,8 +1,10 @@
 {erl_opts, [warnings_as_errors,
 	    {platform_define, "^2[0-1]{1}", fsm_deprecated},
             {platform_define, "^1[7-8]{1}", old_rand},
+            {platform_define, "^17", no_log2},
             {platform_define, "^R", no_sync},
             {platform_define, "^R", old_rand},
+            {platform_define, "^R", no_log2},
             {platform_define, "^R", slow_test}]}.
 
 {xref_checks, [undefined_function_calls,undefined_functions]}.
diff --git a/src/leveled_math.erl b/src/leveled_math.erl
new file mode 100644
index 0000000..f88ed4f
--- /dev/null
+++ b/src/leveled_math.erl
@@ -0,0 +1,38 @@
+%% Handle missing log2 prior to OTP18
+
+-module(leveled_math).
+
+%% API
+-export([
+         log2/1
+        ]).
+
+
+-include_lib("eunit/include/eunit.hrl").
+
+%%%===================================================================
+%%% Use log2
+%%%===================================================================
+-ifndef(no_log2).
+
+log2(X) ->
+    math:log2(X).
+
+-else.
+%%%===================================================================
+%%% Old (r18) random style functions
+%%%===================================================================
+
+log2(X) ->
+    math:log(X) / 0.6931471805599453.
+
+-endif.
+
+
+-ifdef(TEST).
+
+log2_test() ->
+    ?assertMatch(8, round(log2(256))),
+    ?assertMatch(16, round(log2(65536))).
+
+-endif.
diff --git a/src/leveled_tictac.erl b/src/leveled_tictac.erl
index 85ada1d..e9716c0 100644
--- a/src/leveled_tictac.erl
+++ b/src/leveled_tictac.erl
@@ -413,7 +413,7 @@ adjust_segmentmatch_list(SegmentList, CompareSize, StoreSize) ->
     StoreSizeI = get_size(StoreSize),
     if CompareSizeI =< StoreSizeI ->
         ExpItems = StoreSizeI div CompareSizeI - 1,
-        ShiftFactor = trunc(math:log2(CompareSizeI * ?L2_CHUNKSIZE)),
+        ShiftFactor = round(leveled_math:log2(CompareSizeI * ?L2_CHUNKSIZE)),
         ExpList = 
             lists:map(fun(X) -> X bsl ShiftFactor end, lists:seq(1, ExpItems)),
         UpdSegmentList =