Adding accumulate and plus

doc/sphinx/src/using.rst

@@ -242,6 +242,25 @@ For sufficiently large integer powers, ``std::pow`` may be faster, but testing
 indicates ``int_power`` is significantly faster (roughly a factor of two or
 better) up to power of at least 100.
 
+The function
+
+.. code-block:: cpp
+
+  template <
+    typename IterB,
+    typename IterE,
+    typename Value,
+    typename Op = singe::util::plus<Value>>
+  PORTABLE_FUNCTION constexpr Value accumulate(
+    IterB begin,
+    IterE end,
+    Value accum,
+    Op && op = singe::util::plus<Value>{})
+
+is a simple ``constexpr`` implementation of ``std::accumulate`` from the STL.
+Ports-of-Call also provides a ``constexpr`` implementation of ``std::plus``
+(which is the default operator for ``accumulate``).
+
 macros_arrays.hpp
 ^^^^^^^^^^^^^^^^^^^
 

ports-of-call/math_utils.hpp

@@ -51,6 +51,23 @@ template <typename base_t, typename exp_t>
   return result;
 }
 
+template <typename Value>
+struct plus {
+  PORTABLE_FUNCTION constexpr Value operator()(Value const accum, Value const current) {
+    return accum + current;
+  }
+};
+
+template <typename IterB, typename IterE, typename Value,
+          typename Op = singe::util::plus<Value>>
+PORTABLE_FUNCTION constexpr Value accumulate(IterB begin, IterE end, Value accum,
+                                             Op && op = singe::util::plus<Value>{}) {
+  for (auto iter = begin; iter != end; ++iter) {
+    accum = op(accum, *iter);
+  }
+  return accum;
+}
+
 } // namespace Math
 } // namespace PortsOfCall