[libc] wmemchr implementation (#142640)

Implemented wmemchr and tests.
Fixes: #121183

---------

Co-authored-by: Sriya Pratipati <sriyap@google.com>

libc/test/src/wchar/CMakeLists.txt

@@ -105,6 +105,16 @@ add_libc_test(
     libc.src.wchar.wcsspn
 )
 
+add_libc_test(
+  wmemchr_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wmemchr_test.cpp
+  DEPENDS
+    libc.src.wchar.wmemchr
+)
+
 add_libc_test(
   wmemcmp_test
   SUITE

libc/test/src/wchar/wmemchr_test.cpp

@@ -0,0 +1,92 @@
+//===-- Unittests for wmemchr ---------------------------------------------===//
+//
+// 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/wmemchr.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWMemChrTest, FindsCharacterAfterNullTerminator) {
+  // wmemchr should continue searching after a null terminator.
+  const size_t size = 5;
+  const wchar_t src[size] = {L'a', L'\0', L'b', L'c', L'\0'};
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'b', size), (src + 2));
+}
+
+TEST(LlvmLibcWMemChrTest, FindsCharacterInNonNullTerminatedCollection) {
+  const size_t size = 3;
+  const wchar_t src[size] = {L'a', L'b', L'c'};
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'b', size), (src + 1));
+}
+
+TEST(LlvmLibcWMemChrTest, FindsFirstCharacter) {
+  const size_t size = 6;
+  const wchar_t *src = L"abcde";
+  // Should return original array since 'a' is the first character.
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'a', size), (src));
+}
+
+TEST(LlvmLibcWMemChrTest, FindsMiddleCharacter) {
+  const size_t size = 6;
+  const wchar_t *src = L"abcde";
+  // Should return characters after and including 'c'.
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'c', size), (src + 2));
+}
+
+TEST(LlvmLibcWMemChrTest, FindsLastCharacterThatIsNotNullTerminator) {
+  const size_t size = 6;
+  const wchar_t *src = L"abcde";
+  // Should return 'e' and null terminator.
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'e', size), (src + 4));
+}
+
+TEST(LlvmLibcWMemChrTest, FindsNullTerminator) {
+  const size_t size = 6;
+  const wchar_t *src = L"abcde";
+  // Should return null terminator.
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'\0', size), (src + 5));
+}
+
+TEST(LlvmLibcWMemChrTest, CharacterNotWithinStringShouldReturnNullptr) {
+  const size_t size = 6;
+  const wchar_t *src = L"abcde";
+  // Should return nullptr.
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'z', size), nullptr);
+}
+
+TEST(LlvmLibcWMemChrTest, CharacterNotWithinSizeShouldReturnNullptr) {
+  const size_t size = 3;
+  const wchar_t *src = L"abcde";
+  // Should return nullptr.
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'd', size), nullptr);
+}
+
+TEST(LlvmLibcWMemChrTest, TheSourceShouldNotChange) {
+  const size_t size = 3;
+  const wchar_t *src = L"ab";
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'a', size), src);
+  ASSERT_TRUE(src[0] == L'a');
+  ASSERT_TRUE(src[1] == L'b');
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'c', size), nullptr);
+  ASSERT_TRUE(src[0] == L'a');
+  ASSERT_TRUE(src[1] == L'b');
+}
+
+TEST(LlvmLibcWMemChrTest, EmptyStringShouldOnlyMatchNullTerminator) {
+  const size_t size = 1;
+  const wchar_t *src = L"";
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'\0', size), src);
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'c', size), nullptr);
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'1', size), nullptr);
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'?', size), nullptr);
+}
+
+TEST(LlvmLibcWMemChrTest, SingleRepeatedCharacterShouldReturnFirst) {
+  const size_t size = 6;
+  const wchar_t *src = L"XXXXX";
+  ASSERT_EQ(LIBC_NAMESPACE::wmemchr(src, L'X', size), src);
+}