[libc] Implemented wctomb

libc/config/linux/x86_64/entrypoints.txt

@@ -1248,6 +1248,7 @@ if(LLVM_LIBC_FULL_BUILD)
     # wchar.h entrypoints
     libc.src.wchar.mbrtowc
     libc.src.wchar.wcrtomb
+    libc.src.wchar.wctomb
   )
 endif()
 

libc/include/wchar.yaml

@@ -167,6 +167,13 @@ functions:
       - type: char *__restrict
       - type: wchar_t
       - type: mbstate_t *__restrict
+  - name: wctomb
+    standards:
+      - stdc
+    return_type: int
+    arguments:
+      - type: char *
+      - type: wchar_t
   - name: wcscpy
     standards:
       - stdc

libc/src/wchar/CMakeLists.txt

@@ -48,6 +48,19 @@ add_entrypoint_object(
     libc.src.__support.wchar.mbstate
 )
 
+add_entrypoint_object(
+  wctomb
+  SRCS
+    wctomb.cpp
+  HDRS
+    wctomb.h
+  DEPENDS
+    libc.hdr.types.wchar_t
+    libc.src.__support.wchar.wcrtomb
+    libc.src.__support.wchar.mbstate
+    libc.src.__support.libc_errno
+)
+
 add_entrypoint_object(
   mbrtowc
   SRCS

libc/src/wchar/wctomb.cpp

@@ -0,0 +1,35 @@
+//===-- Implementation of wctomb ------------------------------------------===//
+//
+// 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/wctomb.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/mbstate.h"
+#include "src/__support/wchar/wcrtomb.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, wctomb, (char *s, wchar_t wc)) {
+  internal::mbstate internal_mbstate;
+  if (s == nullptr)
+    return 0;
+
+  auto result = internal::wcrtomb(s, wc, &internal_mbstate);
+
+  if (!result.has_value()) { // invalid wide character
+    libc_errno = EILSEQ;
+    return -1;
+  }
+
+  return static_cast<int>(result.value());
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/wchar/wctomb.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for wctomb ------------------------*- C++ -*-===//
+//
+// 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_WCTOMB_H
+#define LLVM_LIBC_SRC_WCHAR_WCTOMB_H
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int wctomb(char *s, wchar_t wc);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_WCTOMB_H

libc/test/src/wchar/CMakeLists.txt

@@ -61,6 +61,17 @@ add_libc_test(
     libc.src.__support.libc_errno
 )
 
+add_libc_test(
+  wctomb_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wctomb_test.cpp
+  DEPENDS
+    libc.src.wchar.wctomb
+    libc.hdr.types.wchar_t
+)
+
 add_libc_test(
   wmemset_test 
   SUITE

libc/test/src/wchar/wctomb_test.cpp

@@ -0,0 +1,73 @@
+//===-- Unittests for wctomb ----------------------------------------------===//
+//
+// 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/__support/libc_errno.h"
+#include "src/wchar/wctomb.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcWCToMBTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST(LlvmLibcWCToMBTest, OneByte) {
+  wchar_t wc = L'U';
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 1);
+  ASSERT_EQ(mb[0], 'U');
+}
+
+TEST(LlvmLibcWCToMBTest, TwoByte) {
+  // testing utf32: 0xff -> utf8: 0xc3 0xbf
+  wchar_t wc = 0xff;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 2);
+  ASSERT_EQ(mb[0], static_cast<char>(0xc3));
+  ASSERT_EQ(mb[1], static_cast<char>(0xbf));
+}
+
+TEST(LlvmLibcWCToMBTest, ThreeByte) {
+  // testing utf32: 0xac15 -> utf8: 0xea 0xb0 0x95
+  wchar_t wc = 0xac15;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 3);
+  ASSERT_EQ(mb[0], static_cast<char>(0xea));
+  ASSERT_EQ(mb[1], static_cast<char>(0xb0));
+  ASSERT_EQ(mb[2], static_cast<char>(0x95));
+}
+
+TEST(LlvmLibcWCToMBTest, FourByte) {
+  // testing utf32: 0x1f921 -> utf8: 0xf0 0x9f 0xa4 0xa1
+  wchar_t wc = 0x1f921;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 4);
+  ASSERT_EQ(mb[0], static_cast<char>(0xf0));
+  ASSERT_EQ(mb[1], static_cast<char>(0x9f));
+  ASSERT_EQ(mb[2], static_cast<char>(0xa4));
+  ASSERT_EQ(mb[3], static_cast<char>(0xa1));
+}
+
+TEST(LlvmLibcWCToMBTest, NullString) {
+  wchar_t wc = L'A';
+
+  int cnt = LIBC_NAMESPACE::wctomb(nullptr, wc);
+
+  // no state-dependent encoding
+  ASSERT_EQ(cnt, 0);
+}
+
+TEST(LlvmLibcWCToMBTest, InvalidWchar) {
+  wchar_t wc = 0x12ffff;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+}