Traditional, UNC, and Device Is Absolute?

mrbgems/mruby-io/src/file.c

@@ -281,52 +281,56 @@ mrb_file__getwd(mrb_state *mrb, mrb_value klass)
 }
 
 #ifdef _WIN32
-#define IS_FILESEP(x) (x == FILE_SEPARATOR || x == FILE_ALT_SEPARATOR)
-#define IS_VOLSEP(x) (x == VOLUME_SEPARATOR)
+#define IS_FILESEP(x) (x == (*(char*)(FILE_SEPARATOR)) || x == (*(char*)(FILE_ALT_SEPARATOR)))
+#define IS_VOLSEP(x) (x == (*(char*)(VOLUME_SEPARATOR)))
 #define IS_DEVICEID(x) (x == '.' || x == '?')
+#define CHECK_UNCDEV_PATH (IS_FILESEP(path[0]) && IS_FILESEP(path[1]))
 
 static int 
 is_absolute_traditional_path(const char *path, int len)
 {
   if (len < 3) return 0;
-  if (IS_FILESEP(path[0])) return 1;
   return (ISALPHA(path[0]) && IS_VOLSEP(path[1]) && IS_FILESEP(path[2]));
 }
 
 static int 
 is_aboslute_unc_path(const char *path, int len) {
   if (len < 2) return 0;
-  return (IS_FILESEP(path[0]) && IS_FILESEP(path[1]));
+  return (CHECK_UNCDEV_PATH && !IS_DEVICEID(path[2]));
 }
 
 static int 
 is_absolute_device_path(const char *path, int len) {
   if (len < 4) return 0;
-  return (is_aboslute_unc_path(path, len) && IS_DEVICEID(path[2]) && IS_FILESEP(path[3]));
+  return (CHECK_UNCDEV_PATH && IS_DEVICEID(path[2]) && IS_FILESEP(path[3]));
 }
 
 static int
 mrb_file_is_absolute_path(const char *path, int len)
 {
-  return (
-    is_absolute_traditional_path(path, len) || 
-    is_aboslute_unc_path(path, len) || 
-    is_absolute_device_path(path, len)
-  );
+  if (IS_FILESEP(path[0])) return 1;
+  if (len > 0)
+    return (
+      is_absolute_traditional_path(path, len) || 
+      is_aboslute_unc_path(path, len) || 
+      is_absolute_device_path(path, len)
+      );
+  else
+    return 0;
+}
 
 #undef IS_FILESEP
 #undef IS_VOLSEP
 #undef IS_DEVICEID
+#undef CHECK_UNCDEV_PATH
 
 #else
 static int
 mrb_file_is_absolute_path(const char *path)
 {
-#define IS_FILESEP(x) (x == FILE_SEPARATOR)
-  return IS_FILESEP(path[0]);
-#undef IS_FILESEP
-#endif
+  return (path[0] == *(char*)(FILE_SEPARATOR));
 }
+#endif
 
 static mrb_value
 mrb_file__gethome(mrb_state *mrb, mrb_value klass)