# HG changeset patch
# User jbe
# Date 1407971484 -7200
# Node ID 035b58aa430a39af02fbde0b439ba2d35b9942e2
# Parent  9fd7e1bf9fe31e2e1c0730b52ff7014418334c89
Improve performance of pairs and ipairs in JSON library

diff -r 9fd7e1bf9fe3 -r 035b58aa430a libraries/json/json.c
--- a/libraries/json/json.c	Tue Aug 12 01:01:54 2014 +0200
+++ b/libraries/json/json.c	Thu Aug 14 01:11:24 2014 +0200
@@ -865,12 +865,7 @@
 static int json_pairs_iterfunc(lua_State *L) {
   // stack shall contain two function arguments:
   lua_settop(L, 2);
-  // replace first argument with its shadow table
-  // or throw error if no shadow table is found:
-  json_getshadow(L, 1);
-  if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
-  lua_replace(L, 1);
-  // get next key value pair from shadow table (using previous key from argument 2)
+  // get next key value pair from shadow table (argument 1) using previous key (argument 2)
   // and return nothing if there is no next pair:
   if (!lua_next(L, 1)) return 0;
   // replace null-marker with nil:
@@ -887,9 +882,10 @@
 static int json_pairs(lua_State *L) {
   // require one argument to function
   luaL_checkany(L, 1);
-  // return triple of function json_pairs_iterfunc, first argument, and nil:
+  // return triple of function json_pairs_iterfunc, shadow table of first argument, and nil:
   lua_pushcfunction(L, json_pairs_iterfunc);
-  lua_pushvalue(L, 1);
+  json_getshadow(L, 1);
+  if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
   lua_pushnil(L);
   return 3;
 }
@@ -901,20 +897,16 @@
   lua_settop(L, 2);
   // calculate new index by incrementing second argument:
   idx = lua_tointeger(L, 2) + 1;
-  // push shadow table onto stack position 3
-  // or throw error if no shadow table is found:
-  json_getshadow(L, 1);
-  if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
-  // do integer lookup in shadow table and store result on stack position 4:
-  lua_rawgeti(L, 3, idx);
+  // do integer lookup in shadow table and store result on stack position 3:
+  lua_rawgeti(L, 1, idx);
   // return nothing if there was no value:
-  if (lua_isnil(L, 4)) return 0;
+  if (lua_isnil(L, 3)) return 0;
   // return new index and
   // 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 (json_isnullmark(L, 4)) lua_pushnil(L);
-  else lua_pushvalue(L, 4);
+  if (json_isnullmark(L, 3)) lua_pushnil(L);
+  else lua_pushvalue(L, 3);
   return 2;
 }
 
@@ -923,9 +915,10 @@
 static int json_ipairs(lua_State *L) {
   // require one argument to function
   luaL_checkany(L, 1);
-  // return triple of function json_ipairs_iterfunc, first argument, and zero:
+  // return triple of function json_ipairs_iterfunc, shadow table of first argument, and zero:
   lua_pushcfunction(L, json_ipairs_iterfunc);
-  lua_pushvalue(L, 1);
+  json_getshadow(L, 1);
+  if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
   lua_pushinteger(L, 0);
   return 3;
 }