[algs] Add hash for 64bit ints

src/hb-algs.hh

@@ -315,10 +315,15 @@ struct
   impl (const T& v, hb_priority<2>) const HB_RETURN (uint32_t, hb_deref (v).hash ())
 
   // Horrible: std:hash() of integers seems to be identity in gcc / clang?!
+  //
   template <typename T,
-	    hb_enable_if (std::is_integral<T>::value)> constexpr auto
+	    hb_enable_if (std::is_integral<T>::value && sizeof (T) <= sizeof (uint32_t))> constexpr auto
   impl (const T& v, hb_priority<1>) const HB_RETURN (uint32_t, v * 8388607u /* Mersenne prime */)
 
+  template <typename T,
+	    hb_enable_if (std::is_integral<T>::value && sizeof (T) > sizeof (uint32_t))> constexpr auto
+  impl (const T& v, hb_priority<1>) const HB_RETURN (uint32_t, (v * 8388607u) ^ ((v >> 32) * 8388607u) /* Mersenne prime */)
+
   template <typename T> constexpr auto
   impl (const T& v, hb_priority<0>) const HB_RETURN (uint32_t, std::hash<hb_decay<decltype (hb_deref (v))>>{} (hb_deref (v)))