[libc] Implemented wmempcpy (#142067)

Implemented wmempcpy and added tests

libc/test/src/wchar/CMakeLists.txt

@@ -85,6 +85,16 @@ add_libc_test(
     libc.src.wchar.wmemcmp
 )
 
+add_libc_test(
+  wmempcpy_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wmempcpy_test.cpp
+  DEPENDS
+    libc.src.wchar.wmempcpy
+)
+
 add_libc_test(
   wmemcpy_test
   SUITE

libc/test/src/wchar/wmempcpy_test.cpp

@@ -0,0 +1,50 @@
+//===-- Unittests for wmempcpy --------------------------------------------===//
+//
+// 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/wmempcpy.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWMempcpyTest, Simple) {
+  const wchar_t *src = L"12345";
+  wchar_t dest[10] = {};
+  void *result = LIBC_NAMESPACE::wmempcpy(dest, src, 6);
+  ASSERT_EQ(static_cast<wchar_t *>(result), dest + 6);
+
+  ASSERT_TRUE(dest[0] == src[0]);
+  ASSERT_TRUE(dest[1] == src[1]);
+  ASSERT_TRUE(dest[2] == src[2]);
+  ASSERT_TRUE(dest[3] == src[3]);
+  ASSERT_TRUE(dest[4] == src[4]);
+  ASSERT_TRUE(dest[5] == src[5]);
+}
+
+TEST(LlvmLibcWmempcpyTest, ZeroCount) {
+  const wchar_t *src = L"12345";
+  wchar_t dest[5] = {};
+  void *result = LIBC_NAMESPACE::wmempcpy(dest, src, 0);
+  ASSERT_EQ(static_cast<wchar_t *>(result), dest);
+
+  ASSERT_TRUE(dest[0] == 0);
+  ASSERT_TRUE(dest[1] == 0);
+  ASSERT_TRUE(dest[2] == 0);
+  ASSERT_TRUE(dest[3] == 0);
+  ASSERT_TRUE(dest[4] == 0);
+}
+
+TEST(LlvmLibcWMempcpyTest, BoundaryCheck) {
+  const wchar_t *src = L"12345";
+  wchar_t dest[4] = {};
+  void *result = LIBC_NAMESPACE::wmempcpy(dest + 1, src + 1, 2);
+
+  ASSERT_TRUE(dest[0] == 0);
+  ASSERT_TRUE(dest[1] == src[1]);
+  ASSERT_TRUE(dest[2] == src[2]);
+  ASSERT_TRUE(dest[3] == 0);
+
+  ASSERT_EQ(static_cast<wchar_t *>(result), dest + 3);
+}