1 files changed, 56 insertions, 0 deletions
diff --git a/core/src/xmake/utf8/offset.c b/core/src/xmake/utf8/offset.c
new file mode 100644
index 000000000..fcd155af7
--- /dev/null
+++ b/core/src/xmake/utf8/offset.c
@@ -0,0 +1,56 @@
+/*!A cross-platform build utility based on Lua
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright (C) 2015-present, Xmake Open Source Community.
+ *
+ * @author      ruki
+ * @file        offset.c
+ *
+ */
+
+/* //////////////////////////////////////////////////////////////////////////////////////
+ * includes
+ */
+#include "utf8.h"
+
+/* //////////////////////////////////////////////////////////////////////////////////////
+ * implementation
+ */
+
+/* offset(s, n, [i])  -> index where n-th character counting from
+ *   position 'i' starts; 0 means character at 'i'.
+ */
+tb_int_t xm_utf8_offset(lua_State *lua) {
+    tb_assert_and_check_return_val(lua, 0);
+
+    size_t len;
+    tb_char_t const* s = luaL_checklstring(lua, 1, &len);
+    lua_Integer n  = luaL_checkinteger(lua, 2);
+    lua_Integer posi = (n >= 0) ? 1 : len + 1;
+    posi = xm_utf8_posrelat((tb_long_t)luaL_optinteger(lua, 3, posi), len);
+
+    tb_long_t result = xm_utf8_offset_impl(s, len, (tb_long_t)n, (tb_long_t)posi);
+    if (result == -1) {
+        return luaL_argerror(lua, 3, "position out of bounds");
+    }
+    if (result == -2) {
+        return luaL_error(lua, "initial position is a continuation byte");
+    }
+    if (result == 0) {
+        lua_pushnil(lua);
+        return 1;
+    }
+    lua_pushinteger(lua, result);
+    return 1;
+}