1 files changed, 37 insertions, 0 deletions
diff --git a/libc/src/stdlib/mbtowc.cpp b/libc/src/stdlib/mbtowc.cpp
new file mode 100644
index 000000000000..5f482463f471
--- /dev/null
+++ b/libc/src/stdlib/mbtowc.cpp
@@ -0,0 +1,37 @@
+//===-- Implementation of mbtowc -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/mbtowc.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbrtowc.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, mbtowc,
+                   (wchar_t *__restrict pwc, const char *__restrict s,
+                    size_t n)) {
+  // returns 0 since UTF-8 encoding is not state-dependent
+  if (s == nullptr)
+    return 0;
+  internal::mbstate internal_mbstate;
+  auto ret = internal::mbrtowc(pwc, s, n, &internal_mbstate);
+  if (!ret.has_value() || static_cast<int>(ret.value()) == -2) {
+    // Encoding failure
+    libc_errno = EILSEQ;
+    return -1;
+  }
+  return static_cast<int>(ret.value());
+}
+
+} // namespace LIBC_NAMESPACE_DECL