coord: generalise point hashing for all coord types

move the point hashing function into general coord operations. convert
from using std::hash to something we've made so that we know it's going
to spread the bits a little (unlike the default identity of GCC 7).

coord/ops.hpp

@@ -934,9 +934,9 @@ namespace util {
 }
 
 
+///////////////////////////////////////////////////////////////////////////////
 #include <tuple>
 
-
 namespace std {
     /// returns the dimensions of a coordinate type.
     ///
@@ -985,4 +985,35 @@ namespace std {
 }
 
 
+///////////////////////////////////////////////////////////////////////////////
+#include <functional>
+
+#include "../hash.hpp"
+
+namespace std {
+    template <
+        size_t S,
+        typename T,
+        template <
+            std::size_t,typename
+        > class K
+    >
+    struct hash<
+        K<S,T>
+    > : public ::std::enable_if<
+        ::util::is_coord_v<K<S,T>>
+    > {
+        std::size_t
+        operator() (K<S,T> k) const {
+            size_t v = 0xdeadbeef;
+
+            for (auto t: k)
+                v = ::util::hash::mix (t, v);
+
+            return v;
+        }
+    };
+}
+
+
 #endif

point.hpp

@@ -103,23 +103,6 @@ namespace util {
     typedef point4<int> point4i;
 }
 
-#include <functional>
-
-namespace std {
-    template <size_t S, typename T>
-    struct hash<util::point<S,T>> {
-        size_t operator() (util::point<S,T> p) const {
-            std::hash<T> h;
-
-            size_t k = 0;
-            for (size_t i = 0; i < S; ++i)
-                k = h (p.data[i] ^ k);
-
-            return k;
-        }
-    };
-}
-
 #include "point.ipp"
 
 #endif // __UTIL_POINT_HPP