[libc] Implement mbsinit (#150654)

Implemented public libc function to check if an mbstate describes an
empty state

libc/config/linux/x86_64/entrypoints.txt

@@ -1264,6 +1264,7 @@ if(LLVM_LIBC_FULL_BUILD)
     # wchar.h entrypoints
     libc.src.wchar.mblen
     libc.src.wchar.mbrlen
+    libc.src.wchar.mbsinit
     libc.src.wchar.mbrtowc
     libc.src.wchar.mbtowc
     libc.src.wchar.wcrtomb

libc/include/wchar.yaml

@@ -53,6 +53,12 @@ functions:
       - type: wchar_t *__restrict
       - type: const char *__restrict
       - type: size_t
+  - name: mbsinit
+    standards:
+      - stdc
+    return_type: int
+    arguments:
+      - type: mbstate_t *
   - name: mblen
     standards:
       - stdc

libc/src/wchar/CMakeLists.txt

@@ -136,6 +136,21 @@ add_entrypoint_object(
     libc.src.__support.libc_errno
 )
 
+add_entrypoint_object(
+  mbsinit
+  SRCS
+    mbsinit.cpp
+  HDRS
+    mbsinit.h
+  DEPENDS
+    libc.hdr.types.wchar_t
+    libc.hdr.types.mbstate_t
+    libc.src.__support.common
+    libc.src.__support.macros.config
+    libc.src.__support.wchar.character_converter
+    libc.src.__support.wchar.mbstate
+)
+
 add_entrypoint_object(
   mbrtowc
   SRCS

libc/src/wchar/mbsinit.cpp

@@ -0,0 +1,26 @@
+//===-- Implementation of mbsinit -----------------------------------------===//
+//
+// 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/wchar/mbsinit.h"
+
+#include "hdr/types/mbstate_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/character_converter.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, mbsinit, (mbstate_t * ps)) {
+  if (ps == nullptr)
+    return true;
+  internal::CharacterConverter cr(reinterpret_cast<internal::mbstate *>(ps));
+  return cr.isValidState() && cr.isEmpty();
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/wchar/mbsinit.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for mbsinit ---------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_WCHAR_MBSINIT_H
+#define LLVM_LIBC_SRC_WCHAR_MBSINIT_H
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int mbsinit(mbstate_t *ps);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_MBSINIT_H

libc/test/src/wchar/CMakeLists.txt

@@ -99,7 +99,22 @@ add_libc_test(
     libc.src.string.memset
     libc.src.wchar.mbrlen
     libc.hdr.types.mbstate_t
+    libc.hdr.types.wchar_t
     libc.test.UnitTest.ErrnoCheckingTest
+)   
+
+add_libc_test(
+  mbsinit_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    mbsinit_test.cpp
+  DEPENDS
+    libc.src.string.memset
+    libc.src.wchar.mbsinit
+    libc.src.wchar.mbrtowc
+    libc.hdr.types.mbstate_t
+    libc.hdr.types.wchar_t
 )
 
 add_libc_test(

libc/test/src/wchar/mbsinit_test.cpp

@@ -0,0 +1,33 @@
+//===-- Unittests for mbsinit ---------------------------------------------===//
+//
+// 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 "hdr/types/wchar_t.h"
+#include "src/string/memset.h"
+#include "src/wchar/mbrtowc.h"
+#include "src/wchar/mbsinit.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcMBSInitTest, EmptyState) {
+  mbstate_t ps;
+  LIBC_NAMESPACE::memset(&ps, 0, sizeof(mbstate_t));
+  ASSERT_NE(LIBC_NAMESPACE::mbsinit(&ps), 0);
+  ASSERT_NE(LIBC_NAMESPACE::mbsinit(nullptr), 0);
+}
+
+TEST(LlvmLibcMBSInitTest, ConversionTest) {
+  const char *src = "\xf0\x9f\xa4\xa3"; // 4 byte emoji
+  wchar_t dest[2];
+  mbstate_t ps;
+  LIBC_NAMESPACE::memset(&ps, 0, sizeof(mbstate_t));
+
+  ASSERT_NE(LIBC_NAMESPACE::mbsinit(&ps), 0);
+  LIBC_NAMESPACE::mbrtowc(dest, src, 2, &ps); // partial conversion
+  ASSERT_EQ(LIBC_NAMESPACE::mbsinit(&ps), 0);
+  LIBC_NAMESPACE::mbrtowc(dest, src + 2, 2, &ps); // complete conversion
+  ASSERT_NE(LIBC_NAMESPACE::mbsinit(&ps), 0);     // state should be reset now
+}