# HG changeset patch
# User jbe
# Date 1406769484 -7200
# Node ID 185e944182cb488c9e482b4f08bb08af2f9d1d47
# Parent  c8669dde9ce200c7b890083b6463c290dfebec53
Better C macros for null-marker in JSON library

diff -r c8669dde9ce2 -r 185e944182cb libraries/json/json.c
--- a/libraries/json/json.c	Thu Jul 31 03:01:53 2014 +0200
+++ b/libraries/json/json.c	Thu Jul 31 03:18:04 2014 +0200
@@ -14,21 +14,19 @@
 //       returning nil and an error string).
 #define JSON_MAXDEPTH 500
 
+// generate dummy memory addresses that represents null values:
+char json_nullmark;
+#define json_isnullmark(L, i) (lua_touserdata((L), (i)) == &json_nullmark)
+#define json_pushnullmark(L) lua_pushlightuserdata((L), &json_nullmark)
+
 // macros for usage of Lua registry:
 #define JSON_REGENT char
 #define JSON_REGPOINTER void *
-#define json_pushlightref(L, x) lua_pushlightuserdata((L), &json_reference.x)
-#define json_islightref(L, i, x) (lua_touserdata((L), (i)) == &json_reference.x)
 #define json_regpointer(x) (&json_registry.x)
 #define json_regfetchpointer(L, x) lua_rawgetp((L), LUA_REGISTRYINDEX, (x))
 #define json_regfetch(L, x) json_regfetchpointer(L, json_regpointer(x))
 #define json_regstore(L, x) lua_rawsetp(L, LUA_REGISTRYINDEX, json_regpointer(x))
 
-// generate dummy memory addresses that represent non-modifiable lightuserdata (dummy) objects:
-static struct {
-  JSON_REGENT nullmark;  // magic value to indicate JSON null value in shadow table
-} json_reference;
-
 // generate dummy memory addresses that represent Lua objects
 // via lightuserdata keys and LUA_REGISTRYINDEX:
 static struct {
@@ -109,7 +107,6 @@
 #define json_import_objectmt_idx 2
 #define json_import_arraymt_idx 3
 #define json_import_shadowtbl_idx 4
-#define json_import_nullmark_idx 5
 
 // decodes a JSON document:
 static int json_import(lua_State *L) {
@@ -131,8 +128,6 @@
   json_regfetch(L, arraymt);
   // push shadowtbl onto stack position 4:
   json_regfetch(L, shadowtbl);
-  // push nullmark onto stack position 5:
-  json_pushlightref(L, nullmark);
   // require string as first argument:
   str = luaL_checklstring(L, 1, &total);
   // if string contains a NULL byte, this is a syntax error
@@ -386,7 +381,7 @@
     if (level) {
       // if sub-level,
       // push special null-marker onto stack:
-      lua_pushvalue(L, json_import_nullmark_idx);
+      json_pushnullmark(L);
     } else {
       // if top-level,
       // push nil onto stack:
@@ -446,10 +441,9 @@
 
 // special Lua stack indicies for json_path function:
 #define json_path_shadowtbl_idx 1
-#define json_path_nullmark_idx 2
 
 // stack offset of arguments to json_path function:
-#define json_path_idxshift 2
+#define json_path_idxshift 1
 
 // gets a value or its type from a JSON document (passed as first argument)
 // using a path (passed as variable number of keys after first argument):
@@ -459,9 +453,6 @@
   // insert shadowtbl into stack at position 1 (shifting the arguments):
   json_regfetch(L, shadowtbl);
   lua_insert(L, 1);
-  // insert nullmark into stack at position 2 (shifting the arguments):
-  json_pushlightref(L, nullmark);
-  lua_insert(L, 2);
   // store stack index of top of stack:
   stacktop = lua_gettop(L);
   // use first argument as "current value" (stored on top of stack):
@@ -501,11 +492,11 @@
   if (!type_mode) {
     // if a value (and not its type) was requested,
     // check if value is the null-marker, and store nil on top of Lua stack in that case:
-    if (lua_rawequal(L, -1, json_path_nullmark_idx)) lua_pushnil(L);
+    if (json_isnullmark(L, -1)) lua_pushnil(L);
   } else {
     // if the type was requested,
     // check if value is the null-marker:
-    if (lua_rawequal(L, -1, json_path_nullmark_idx)) {
+    if (json_isnullmark(L, -1)) {
       // if yes, store string "null" on top of Lua stack:
       lua_pushliteral(L, "null");
     } else {
@@ -608,7 +599,7 @@
   }
   // push key (second argument) and null-marker after shadow table onto stack:
   lua_pushvalue(L, 2);
-  json_pushlightref(L, nullmark);
+  json_pushnullmark(L);
   // store key and null-marker in shadow table:
   lua_rawset(L, -3);
   // return nothing:
@@ -628,27 +619,20 @@
   return 1;
 }
 
-// special Lua stack indicies for json_index function:
-#define json_index_nullmark_idx 3
-#define json_index_shadowtbl_idx 4
-
 static int json_index(lua_State *L) {
   // stack shall contain two function arguments:
   lua_settop(L, 2);
-  // push nullmark onto stack position 3:
-  json_pushlightref(L, nullmark);
-  // push shadowtbl onto stack position 4:
+  // get corresponding shadow table for first argument:
   json_regfetch(L, shadowtbl);
-  // get corresponding shadow table for first argument:
   lua_pushvalue(L, 1);
-  lua_rawget(L, json_index_shadowtbl_idx);
+  lua_rawget(L, -2);
   // throw error if no shadow table was found:
   if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
   // use key passed as second argument to lookup value in shadow table:
   lua_pushvalue(L, 2);
   lua_rawget(L, -2);
   // if value is null-marker, then push nil onto stack:
-  if (lua_rawequal(L, -1, json_index_nullmark_idx)) lua_pushnil(L);
+  if (json_isnullmark(L, -1)) lua_pushnil(L);
   // return either looked up value, or nil
   return 1;
 }
@@ -671,20 +655,13 @@
   return 0;
 }
 
-// special Lua stack indicies for json_pairs_iterfunc function:
-#define json_pairs_iterfunc_nullmark_idx 3
-#define json_pairs_iterfunc_shadowtbl_idx 4
-
 static int json_pairs_iterfunc(lua_State *L) {
   // stack shall contain two function arguments:
   lua_settop(L, 2);
-  // push nullmark onto stack position 3:
-  json_pushlightref(L, nullmark);
-  // push shadowtbl onto stack position 4:
+  // get corresponding shadow table for first argument:
   json_regfetch(L, shadowtbl);
-  // get corresponding shadow table for first argument:
   lua_pushvalue(L, 1);
-  lua_rawget(L, json_pairs_iterfunc_shadowtbl_idx);
+  lua_rawget(L, -2);
   // throw error if no shadow table was found:
   if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
   // get next key value pair from shadow table (using previous key from argument 2)
@@ -692,7 +669,7 @@
   lua_pushvalue(L, 2);
   if (!lua_next(L, -2)) return 0;
   // replace null-marker with nil:
-  if (lua_rawequal(L, -1, json_pairs_iterfunc_nullmark_idx)) {
+  if (json_isnullmark(L, -1)) {
     lua_pop(L, 1);
     lua_pushnil(L);
   }
@@ -710,23 +687,16 @@
   return 3;
 }
 
-// special Lua stack indicies for json_ipairs_iterfunc function:
-#define json_ipairs_iterfunc_nullmark_idx 3
-#define json_ipairs_iterfunc_shadowtbl_idx 4
-
 static int json_ipairs_iterfunc(lua_State *L) {
   lua_Integer idx;
   // stack shall contain two function arguments:
   lua_settop(L, 2);
-  // push nullmark onto stack position 3:
-  json_pushlightref(L, nullmark);
-  // push shadowtbl onto stack position 4:
-  json_regfetch(L, shadowtbl);
   // calculate new index by incrementing second argument:
   idx = lua_tointeger(L, 2) + 1;
   // get corresponding shadow table for first argument:
+  json_regfetch(L, shadowtbl);
   lua_pushvalue(L, 1);
-  lua_rawget(L, json_ipairs_iterfunc_shadowtbl_idx);
+  lua_rawget(L, -2);
   // throw error if no shadow table was found:
   if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
   // do integer lookup in shadow table:
@@ -737,7 +707,7 @@
   // either the looked up value if it is not equal to the null-marker
   // or nil instead of null-marker:
   lua_pushinteger(L, idx);
-  if (lua_rawequal(L, -2, json_ipairs_iterfunc_nullmark_idx)) lua_pushnil(L);
+  if (json_isnullmark(L, -2)) lua_pushnil(L);
   else lua_pushvalue(L, -2);
   return 2;
 }
@@ -852,7 +822,7 @@
           lua_call(L, 1, 1);
           luaL_addvalue(&buf);
           luaL_addchar(&buf, ':');
-          if (json_islightref(L, 3, nullmark)) {
+          if (json_isnullmark(L, 3)) {
             luaL_addstring(&buf, "null");
           } else {
             lua_pushcfunction(L, json_export);