Merge pull request #3475 from mapycz/logarithm

Add support for natural logarithm in expressions (via @talaj)

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())
         ;

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
 {

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)