[libc] wcpncpy implementation

libc/config/linux/x86_64/entrypoints.txt

@@ -385,6 +385,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.wchar.wcscpy
     libc.src.wchar.wmemchr
     libc.src.wchar.wcpcpy
+    libc.src.wchar.wcpncpy
 
     # sys/uio.h entrypoints
     libc.src.sys.uio.writev

libc/include/wchar.yaml

@@ -181,3 +181,11 @@ functions:
     arguments:
       - type: wchar_t *__restrict
       - type: const wchar_t *__restrict
+  - name: wcpncpy
+    standards:
+      - stdc
+    return_type: wchar_t *
+    arguments:
+      - type: wchar_t *__restrict
+      - type: const wchar_t *__restrict
+      - type: size_t

libc/src/wchar/CMakeLists.txt

@@ -88,6 +88,18 @@ add_entrypoint_object(
     libc.src.string.string_utils
 )
 
+add_entrypoint_object(
+  wcpncpy
+  SRCS
+    wcpncpy.cpp
+  HDRS
+    wcpncpy.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.wchar_macros
+    libc.src.__support.macros.null_check
+)   
+
 add_entrypoint_object(
   wcschr
   SRCS

libc/src/wchar/wcpncpy.cpp

@@ -0,0 +1,36 @@
+//===-- Implementation of wcpncpy -----------------------------------------===//
+//
+// 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/wcpncpy.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(wchar_t *, wcpncpy,
+                   (wchar_t *__restrict s1, const wchar_t *__restrict s2,
+                    size_t n)) {
+  if (n) {
+    LIBC_CRASH_ON_NULLPTR(s1);
+    LIBC_CRASH_ON_NULLPTR(s2);
+  }
+  size_t i;
+  // Copy up until \0 is found.
+  for (i = 0; i < n && s2[i] != '\0'; ++i)
+    s1[i] = s2[i];
+  // When n>strlen(src), n-strlen(src) \0 are appended.
+  for (; i < n; ++i)
+    s1[i] = L'\0';
+  return s1 + i;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/wchar/wcpncpy.h

@@ -0,0 +1,23 @@
+//===-- Implementation header for wcpncpy ---------------------------------===//
+//
+// 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_WCPNCPY_H
+#define LLVM_LIBC_SRC_WCHAR_WCPNCPY_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+wchar_t *wcpncpy(wchar_t *__restrict ws1, const wchar_t *__restrict ws2,
+                 size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_WCPNsCPY_H

libc/test/src/wchar/CMakeLists.txt

@@ -242,3 +242,13 @@ add_libc_test(
   DEPENDS
     libc.src.wchar.wcpcpy
 )
+
+add_libc_test(
+  wcpncpy_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wcpncpy_test.cpp
+  DEPENDS
+    libc.src.wchar.wcpncpy
+)

libc/test/src/wchar/wcpncpy_test.cpp

@@ -0,0 +1,84 @@
+//===-- Unittests for wcpncpy --------------------------------------------===//
+//
+// 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/wcpncpy.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWCPNCpyTest, EmptySrc) {
+  // Empty src should lead to empty destination.
+  wchar_t dest[4] = {L'a', L'b', L'c', L'\0'};
+  const wchar_t *src = L"";
+  LIBC_NAMESPACE::wcpncpy(dest, src, 3);
+  ASSERT_TRUE(dest[0] == src[0]);
+  ASSERT_TRUE(dest[0] == L'\0');
+  // Rest should also be padded with L'\0'
+  ASSERT_TRUE(dest[1] == L'\0');
+  ASSERT_TRUE(dest[2] == L'\0');
+}
+
+TEST(LlvmLibcWCPNCpyTest, Untouched) {
+  wchar_t dest[] = {L'a', L'b'};
+  const wchar_t src[] = {L'x', L'\0'};
+  LIBC_NAMESPACE::wcpncpy(dest, src, 0);
+  ASSERT_TRUE(dest[0] == L'a');
+  ASSERT_TRUE(dest[1] == L'b');
+}
+
+TEST(LlvmLibcWCPNCpyTest, CopyOne) {
+  wchar_t dest[] = {L'a', L'b'};
+  const wchar_t src[] = {L'x', L'y'};
+  wchar_t *res = LIBC_NAMESPACE::wcpncpy(dest, src, 1);
+  ASSERT_TRUE(dest[0] == L'x');
+  ASSERT_TRUE(dest[1] == L'b');
+  ASSERT_EQ(dest + 1, res);
+}
+
+TEST(LlvmLibcWCPNCpyTest, CopyNull) {
+  wchar_t dest[] = {L'a', L'b'};
+  const wchar_t src[] = {L'\0', L'y'};
+  wchar_t *res = LIBC_NAMESPACE::wcpncpy(dest, src, 1);
+  ASSERT_TRUE(dest[0] == L'\0');
+  ASSERT_TRUE(dest[1] == L'b');
+  ASSERT_EQ(dest + 1, res);
+}
+
+TEST(LlvmLibcWCPNCpyTest, CopyPastSrc) {
+  wchar_t dest[] = {L'a', L'b'};
+  const wchar_t src[] = {L'\0', L'y'};
+  wchar_t *res = LIBC_NAMESPACE::wcpncpy(dest, src, 2);
+  ASSERT_TRUE(dest[0] == L'\0');
+  ASSERT_TRUE(dest[1] == L'\0');
+  ASSERT_EQ(dest + 2, res);
+}
+
+TEST(LlvmLibcWCPNCpyTest, CopyTwoNoNull) {
+  wchar_t dest[] = {L'a', L'b'};
+  const wchar_t src[] = {L'x', L'y'};
+  wchar_t *res = LIBC_NAMESPACE::wcpncpy(dest, src, 2);
+  ASSERT_TRUE(dest[0] == L'x');
+  ASSERT_TRUE(dest[1] == L'y');
+  ASSERT_EQ(dest + 2, res);
+}
+
+TEST(LlvmLibcWCPNCpyTest, CopyTwoWithNull) {
+  wchar_t dest[] = {L'a', L'b'};
+  const wchar_t src[] = {L'x', L'\0'};
+  wchar_t *res = LIBC_NAMESPACE::wcpncpy(dest, src, 2);
+  ASSERT_TRUE(dest[0] == L'x');
+  ASSERT_TRUE(dest[1] == L'\0');
+  ASSERT_EQ(dest + 2, res);
+}
+
+#if defined(LIBC_ADD_NULL_CHECKS) && !defined(LIBC_HAS_SANITIZER)
+TEST(LlvmLibcWCPNCpyTest, NullptrCrash) {
+  // Passing in a nullptr should crash the program.
+  EXPECT_DEATH([] { LIBC_NAMESPACE::wcpncpy(nullptr, nullptr, 1); },
+               WITH_SIGNAL(-1));
+}
+#endif // LIBC_HAS_ADDRESS_SANITIZER