From c1ab5c8e6c899c40fddcb7e3a90053dacc25d99b Mon Sep 17 00:00:00 2001
From: Jiri Drbalek <jiri.drbalek@firma.seznam.cz>
Date: Mon, 1 Aug 2016 12:42:57 +0000
Subject: [PATCH] add support for natural logarithm function in expressions

---
 include/mapnik/expression_grammar_impl.hpp |  1 +
 include/mapnik/function_call.hpp           | 11 +++++++++++
 test/unit/core/expressions_test.cpp        |  3 +++
 3 files changed, 15 insertions(+)

diff --git a/include/mapnik/expression_grammar_impl.hpp b/include/mapnik/expression_grammar_impl.hpp
index 40be6b995..ad28f0135 100644
--- a/include/mapnik/expression_grammar_impl.hpp
+++ b/include/mapnik/expression_grammar_impl.hpp
@@ -102,6 +102,7 @@ unary_function_types::unary_function_types()
         ("tan",  tan_impl())
         ("atan", atan_impl())
         ("exp",  exp_impl())
+        ("log",  log_impl())
         ("abs",  abs_impl())
         ("length",length_impl())
         ;
diff --git a/include/mapnik/function_call.hpp b/include/mapnik/function_call.hpp
index efbaa5f28..f50829bd6 100644
--- a/include/mapnik/function_call.hpp
+++ b/include/mapnik/function_call.hpp
@@ -50,6 +50,17 @@ struct exp_impl
 
 };
 
+// log
+struct log_impl
+{
+    //using type = T;
+    value_type operator() (value_type const& val) const
+    {
+        return std::log(val.to_double());
+    }
+
+};
+
 // sin
 struct sin_impl
 {
diff --git a/test/unit/core/expressions_test.cpp b/test/unit/core/expressions_test.cpp
index 64cdd9ecf..e60d6127b 100644
--- a/test/unit/core/expressions_test.cpp
+++ b/test/unit/core/expressions_test.cpp
@@ -108,6 +108,9 @@ TEST_CASE("expressions")
     TRY_CHECK(eval(" rad_to_deg * atan(1.0) ").to_double() == approx(45.0));
     // exp
     TRY_CHECK(eval(" exp(0.0) ") == 1.0);
+    // log
+    TRY_CHECK(eval(" log(1.0) ") == 0.0);
+    TRY_CHECK(eval(" log(exp(1.0)) ") == 1.0);
     // abs
     TRY_CHECK(eval(" abs(cos(-pi)) ") == 1.0);
     // length (string)