Slightly better documentation for LUAI_MAXALIGN

2 files changed, 15 insertions, 4 deletions

diff --git a/luaconf.h b/luaconf.h
index 7f2206d0..5ac9d988 100644
--- a/luaconf.h
+++ b/luaconf.h
@@ -736,10 +736,17 @@
 
 
 /*
-@@ LUAI_MAXALIGN defines fields that, when used in a union, ensure
-** maximum alignment for the other items in that union.
+@@ LUAI_MAXALIGN defines fields that ensure proper alignment for
+** memory areas offered by Lua (e.g., userdata memory).
+** Add fields to it if you need alignment for non-ISO objects.
 */
+#if defined(LLONG_MAX)
+/* use ISO C99 stuff */
+#define LUAI_MAXALIGN long double u; void *s; long long l
+#else
+/* use only C89 stuff */
 #define LUAI_MAXALIGN  lua_Number n; double u; void *s; lua_Integer i; long l
+#endif
 
 /* }================================================================== */
 
diff --git a/manual/manual.of b/manual/manual.of
index 18c187f4..5eb2fb1f 100644
--- a/manual/manual.of
+++ b/manual/manual.of
@@ -3915,8 +3915,12 @@ like any Lua object.
 This function creates and pushes on the stack a new full userdata,
 with @id{nuvalue} associated Lua values, called @id{user values},
 plus an associated block of raw memory with @id{size} bytes.
-(The user values can be set and read with the functions
-@Lid{lua_setiuservalue} and @Lid{lua_getiuservalue}.)
+
+The user values can be set and read with the functions
+@Lid{lua_setiuservalue} and @Lid{lua_getiuservalue}.
+The block of memory is suitably aligned for any @N{ISO C} object.
+(See macro @id{LUAI_MAXALIGN} in file @id{luaconf.h} for other
+alignment requirements.)
 
 The function returns the address of the block of memory.
 Lua ensures that this address is valid as long as