msvcrt: Add support for multi-byte characters in _mbctolower_l.

dlls/msvcrt/mbcs.c

@@ -451,12 +451,34 @@ unsigned int CDECL _mbsnextc(const unsigned char* str)
  */
 unsigned int CDECL _mbctolower_l(unsigned int c, _locale_t locale)
 {
-    if (_ismbblead_l(c, locale))
+    unsigned char str[2], ret[2];
+    pthreadmbcinfo mbcinfo;
+
+    if(!locale)
+        mbcinfo = get_mbcinfo();
+    else
+        mbcinfo = locale->mbcinfo;
+
+    if (c > 0xff)
     {
-      FIXME("Handle MBC chars\n");
-      return c;
+        if (!_ismbblead_l((c >> 8) & 0xff, locale))
+            return c;
+
+        str[0] = c >> 8;
+        str[1] = c;
+        switch(__crtLCMapStringA(mbcinfo->mblcid, LCMAP_LOWERCASE,
+                    (char*)str, 2, (char*)ret, 2, mbcinfo->mbcodepage, 0))
+        {
+        case 0:
+            return c;
+        case 1:
+            return ret[0];
+        default:
+            return ret[1] + (ret[0] << 8);
+        }
     }
-    return _tolower_l(c, locale); /* ASCII CP or SB char */
+
+    return mbcinfo->mbctype[c + 1] & _SBUP ? mbcinfo->mbcasemap[c] : c;
 }
 
 /*********************************************************************

dlls/msvcrt/tests/string.c

@@ -2896,6 +2896,7 @@ static void test__mbslwr_s(void)
 {
     errno_t ret;
     unsigned char buffer[20];
+    int cp = _getmbcp();
 
     if (!p_mbslwr_s)
     {
@@ -2946,6 +2947,14 @@ static void test__mbslwr_s(void)
     ok(!memcmp(buffer, "abcdefgh\0IJKLMNOP", sizeof("abcdefgh\0IJKLMNOP")),
        "Expected the output buffer to be \"abcdefgh\\0IJKLMNOP\", got \"%s\"\n",
        buffer);
+
+    _setmbcp(936);
+    memcpy(buffer, "\xa2\xf1\xa2\xf2Q", sizeof("\xa2\xf1\xa2\xf2Q"));
+    ret = p_mbslwr_s(buffer, sizeof(buffer));
+    ok(ret == 0, "Expected _mbsupr_s to return 0, got %d\n", ret);
+    ok(!memcmp(buffer, "\xa2\xa1\xa2\xa2q", sizeof("\xa2\xa1\xa2\xa2q")),
+            "got %s\n", debugstr_a((char*)buffer));
+    _setmbcp(cp);
 }
 
 static void test__mbstok(void)