From fdf09e81de5e7f1ecfe71f98b56c411073badae8 Mon Sep 17 00:00:00 2001
From: Olivier Girondel <olivier@biniou.info>
Date: Sun, 4 Jan 2015 04:40:55 +0100
Subject: Add math:log2/1

---
 erts/emulator/beam/bif.tab    |  1 +
 erts/emulator/beam/erl_math.c | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

(limited to 'erts/emulator/beam')

diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index aea3224342..1d0d214e77 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -194,6 +194,7 @@ bif math:erf/1
 bif math:erfc/1
 bif math:exp/1
 bif math:log/1
+bif math:log2/1
 bif math:log10/1
 bif math:sqrt/1
 bif math:atan2/2
diff --git a/erts/emulator/beam/erl_math.c b/erts/emulator/beam/erl_math.c
index 16d4fdc09c..9b864628db 100644
--- a/erts/emulator/beam/erl_math.c
+++ b/erts/emulator/beam/erl_math.c
@@ -207,6 +207,24 @@ BIF_RETTYPE math_log_1(BIF_ALIST_1)
     return math_call_1(BIF_P, log, BIF_ARG_1);
 }
 
+#ifdef HAVE_LOG2
+static double
+log2_wrapper(double x)
+{
+    return log2(x);
+}
+#else
+static double
+log2_wrapper(double x)
+{
+    return log(x) / 0.6931471805599453; /* log(2.0); */
+}
+#endif
+
+BIF_RETTYPE math_log2_1(BIF_ALIST_1)
+{
+    return math_call_1(BIF_P, log2_wrapper, BIF_ARG_1);
+}
 
 BIF_RETTYPE math_log10_1(BIF_ALIST_1)
 {
-- 
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