TValue.jsstring can take start and end indexes

2 files changed, 11 insertions, 8 deletions

diff --git a/src/lobject.js b/src/lobject.js
index c2950b6..d713183 100644
--- a/src/lobject.js
+++ b/src/lobject.js
@@ -118,31 +118,32 @@ class TValue {
         return this.ttisnil() || (this.ttisboolean() && this.value === false);
     }
 
-    jsstring() {
+    jsstring(from, to) {
         let u0, u1, u2, u3, u4, u5;
         let idx = 0;
+        let value = this.value.slice(from ? from : 0, to);
 
         var str = '';
         while (1) {
             // For UTF8 byte structure, see http://en.wikipedia.org/wiki/UTF-8#Description and https://www.ietf.org/rfc/rfc2279.txt and https://tools.ietf.org/html/rfc3629
-            u0 = this.value[idx++];
+            u0 = value[idx++];
             if (!u0) return str;
             if (!(u0 & 0x80)) { str += String.fromCharCode(u0); continue; }
-            u1 = this.value[idx++] & 63;
+            u1 = value[idx++] & 63;
             if ((u0 & 0xE0) == 0xC0) { str += String.fromCharCode(((u0 & 31) << 6) | u1); continue; }
-            u2 = this.value[idx++] & 63;
+            u2 = value[idx++] & 63;
             if ((u0 & 0xF0) == 0xE0) {
                 u0 = ((u0 & 15) << 12) | (u1 << 6) | u2;
             } else {
-                u3 = this.value[idx++] & 63;
+                u3 = value[idx++] & 63;
                 if ((u0 & 0xF8) == 0xF0) {
                     u0 = ((u0 & 7) << 18) | (u1 << 12) | (u2 << 6) | u3;
                 } else {
-                    u4 = this.value[idx++] & 63;
+                    u4 = value[idx++] & 63;
                     if ((u0 & 0xFC) == 0xF8) {
                         u0 = ((u0 & 3) << 24) | (u1 << 18) | (u2 << 12) | (u3 << 6) | u4;
                     } else {
-                        u5 = this.value[idx++] & 63;
+                        u5 = value[idx++] & 63;
                         u0 = ((u0 & 1) << 30) | (u1 << 24) | (u2 << 18) | (u3 << 12) | (u4 << 6) | u5;
                     }
                 }
diff --git a/src/lstrlib.js b/src/lstrlib.js
index c6c0dc3..1b62db1 100644
--- a/src/lstrlib.js
+++ b/src/lstrlib.js
@@ -33,13 +33,15 @@ const posrelat = function(pos, len) {
 
 const str_sub = function(L) {
     let s = lauxlib.luaL_checkstring(L, 1);
+    let ts = L.stack[lapi.index2addr_(L, 1)];
+    s = ts.value;
     let l = s.length;
     let start = posrelat(lauxlib.luaL_checkinteger(L, 2), l);
     let end = posrelat(lauxlib.luaL_optinteger(L, 3, -1), l);
     if (start < 1) start = 1;
     if (end > l) end = l;
     if (start <= end)
-        lapi.lua_pushstring(L, s.slice(start - 1, (start - 1) + (end - start + 1)));
+        lapi.lua_pushstring(L, ts.jsstring(start - 1, (start - 1) + (end - start + 1)));
     else lapi.lua_pushliteral(L, "");
     return 1;
 };