From e7e59d4b0e0a463dcf9261f317c64b184f4e8473 Mon Sep 17 00:00:00 2001
From: Bruce Hill <bitbucket@bruce-hill.com>
Date: Sat, 10 Feb 2018 15:56:03 -0800
Subject: [PATCH] Keep tostring on the stack to avoid looking it up multiple
 times in the __tostring loop.

---
 limmutable.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/limmutable.c b/limmutable.c
index 8125c60..02210bd 100644
--- a/limmutable.c
+++ b/limmutable.c
@@ -261,33 +261,35 @@ static int Ltostring(lua_State *L)
     // Stack: [mt, buckets, bucket, inst_udata]
     lua_rawget(L, -2);
     // Stack: [mt, buckets, bucket, inst_table]
-    
+    lua_getglobal(L, "tostring");
+    // Stack: [mt, buckets, bucket, inst_table, tostring]
     lua_getfield(L, -4, "__fields");
-    // Stack: [mt, buckets, bucket, inst_table, fields]
+    // Stack: [mt, buckets, bucket, inst_table, tostring, fields]
     
     lua_pushnil(L);
     int needs_comma = 0;
     while (lua_next(L, -2) != 0) {
-        // Stack: [mt, buckets, bucket, inst_table, fields, i, fieldname]
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, fieldname]
         if (needs_comma) {
             luaL_addstring(&b, ", ");
         } else {
             needs_comma = 1;
         }
-        // Stack: [mt, buckets, bucket, inst_table, fields, i, fieldname]
-        lua_getglobal(L, "tostring");
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, fieldname]
+        lua_pushvalue(L, -4);
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, fieldname, tostring]
         lua_insert(L, -2);
         lua_call(L, 1, 1);
         luaL_addvalue(&b);
-        // Stack: [mt, buckets, bucket, inst_table, fields, i]
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i]
         luaL_addstring(&b, "=");
         lua_rawgeti(L, -3, lua_tonumber(L, -1));
-        // Stack: [mt, buckets, bucket, inst_table, fields, i, value]
-        lua_getglobal(L, "tostring");
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, value]
+        lua_pushvalue(L, -4);
         lua_insert(L, -2);
         lua_call(L, 1, 1);
         luaL_addvalue(&b);
-        // Stack: [mt, buckets, bucket, inst_table, fields, i]
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i]
     }
     luaL_addstring(&b, ")");
     luaL_pushresult(&b);