[UCRT] Import Microsoft.Windows.SDK.CRTSource version 10.0.22621.3

Imported from https://www.nuget.org/packages/Microsoft.Windows.SDK.CRTSource/10.0.22621.3
License: MIT

sdk/lib/ucrt/mbstring/mbslen.cpp

@@ -0,0 +1,61 @@
+/***
+*mbslen.c - Find length of MBCS string
+*
+*       Copyright (c) Microsoft Corporation.  All rights reserved.
+*
+*Purpose:
+*       Find length of MBCS string
+*
+*******************************************************************************/
+#ifndef _MBCS
+    #error This file should only be compiled with _MBCS defined
+#endif
+
+#include <corecrt_internal.h>
+#include <corecrt_internal_mbstring.h>
+#include <locale.h>
+#include <string.h>
+
+/***
+* _mbslen - Find length of MBCS string
+*
+*Purpose:
+*       Find the length of the MBCS string (in characters).
+*
+*Entry:
+*       unsigned char *s = string
+*
+*Exit:
+*       Returns the number of MBCS chars in the string.
+*
+*Exceptions:
+*
+*******************************************************************************/
+
+extern "C" size_t __cdecl _mbslen_l(
+        const unsigned char *s,
+        _locale_t plocinfo
+        )
+{
+        int n;
+        _LocaleUpdate _loc_update(plocinfo);
+
+        if (_loc_update.GetLocaleT()->mbcinfo->ismbcodepage == 0)
+            return strlen((const char *)s);
+
+        for (n = 0; *s; n++, s++) {
+            if ( _ismbblead_l(*s, _loc_update.GetLocaleT()) ) {
+                if (*++s == '\0')
+                    break;
+            }
+        }
+
+        return(n);
+}
+
+extern "C" size_t (__cdecl _mbslen)(
+        const unsigned char *s
+        )
+{
+    return _mbslen_l(s, nullptr);
+}