[libc] Implemented wctomb

[uzairnawaz]

Implemented wctomb by calling internal wcrtomb function
Added tests

[llvmbot]

@llvm/pr-subscribers-libc

Author: Uzair Nawaz (uzairnawaz)

Changes

Implemented wctomb by calling internal wcrtomb function
Added tests

---

Full diff: https://github.com/llvm/llvm-project/pull/145554.diff

7 Files Affected:

• (modified) libc/config/linux/x86_64/entrypoints.txt (+1)
• (modified) libc/include/wchar.yaml (+7)
• (modified) libc/src/wchar/CMakeLists.txt (+12)
• (added) libc/src/wchar/wctomb.cpp (+32)
• (added) libc/src/wchar/wctomb.h (+22)
• (modified) libc/test/src/wchar/CMakeLists.txt (+11)
• (added) libc/test/src/wchar/wctomb_test.cpp (+68)

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 4d94f10196fd7..60f70fcba2448 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/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()
 
diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 64eb381710668..9c798b101b53f 100644
--- a/libc/include/wchar.yaml
+++ b/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
diff --git a/libc/src/wchar/CMakeLists.txt b/libc/src/wchar/CMakeLists.txt
index ec33caccb16d5..812afab66cf87 100644
--- a/libc/src/wchar/CMakeLists.txt
+++ b/libc/src/wchar/CMakeLists.txt
@@ -48,6 +48,18 @@ 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
+)
+
 add_entrypoint_object(
   mbrtowc
   SRCS
diff --git a/libc/src/wchar/wctomb.cpp b/libc/src/wchar/wctomb.cpp
new file mode 100644
index 0000000000000..3278051eb196f
--- /dev/null
+++ b/libc/src/wchar/wctomb.cpp
@@ -0,0 +1,32 @@
+//===-- 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/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
+    return -1;
+
+  return static_cast<int>(result.value());
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/wchar/wctomb.h b/libc/src/wchar/wctomb.h
new file mode 100644
index 0000000000000..02a34e5ad229f
--- /dev/null
+++ b/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
diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index 184e482c895b1..95a4374abf0a2 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/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
diff --git a/libc/test/src/wchar/wctomb_test.cpp b/libc/test/src/wchar/wctomb_test.cpp
new file mode 100644
index 0000000000000..1fcb51b2cb583
--- /dev/null
+++ b/libc/test/src/wchar/wctomb_test.cpp
@@ -0,0 +1,68 @@
+//===-- 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/wchar/wctomb.h"
+#include "test/UnitTest/Test.h"
+
+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);
+}

[sribee8]

Overall pretty good, just need to add errno things

[michaelrj-google]

LGTM