ossl.h: add NUM2UINT64T() macro

As a wrapper of NUM2ULONG() or NUM2ULL(). Converts a Ruby object to
uint64_t, raising an exception if the conversion fails.

Author: rhenium

ext/openssl/ossl.h

@@ -69,6 +69,19 @@ extern VALUE eOSSLError;
   }\
 } while (0)
 
+/*
+ * Type conversions
+ */
+#if !defined(NUM2UINT64T) /* in case Ruby starts to provide */
+#  if SIZEOF_LONG == 8
+#    define NUM2UINT64T(x) ((uint64_t)NUM2ULONG(x))
+#  elif defined(HAVE_LONG_LONG) && SIZEOF_LONG_LONG == 8
+#    define NUM2UINT64T(x) ((uint64_t)NUM2ULL(x))
+#  else
+#    error "unknown platform; no 64-bit width integer"
+#  endif
+#endif
+
 /*
  * Data Conversion
  */