[libc] wcscspn implementation (#146158)

Implemented wcscspn and tests.

---------

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

libc/test/src/wchar/CMakeLists.txt

@@ -183,6 +183,16 @@ add_libc_test(
     libc.src.wchar.wcsspn
 )
 
+add_libc_test(
+  wcscspn_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wcscspn_test.cpp
+  DEPENDS
+    libc.src.wchar.wcscspn
+)
+
 add_libc_test(
   wmemchr_test
   SUITE

libc/test/src/wchar/wcscspn_test.cpp

@@ -0,0 +1,67 @@
+//===-- Unittests for wcscspn ---------------------------------------------===//
+//
+// 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/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/wchar/wcscspn.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWCSCSpnTest, EmptyStringShouldReturnZeroLengthSpan) {
+  // The search should not include the null terminator.
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"", L""), size_t(0));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"_", L""), size_t(1));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"", L"_"), size_t(0));
+}
+
+TEST(LlvmLibcWCSCSpnTest, ShouldNotSpanAnythingAfterNullTerminator) {
+  const wchar_t src[4] = {L'a', L'b', L'\0', L'c'};
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"de"), size_t(2));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"c"), size_t(2));
+
+  // Same goes for the segment to be searched for.
+  const wchar_t segment[4] = {L'1', L'2', L'\0', L'3'};
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"3", segment), size_t(1));
+}
+
+TEST(LlvmLibcWCSCSpnTest, SpanEachIndividualCharacter) {
+  const wchar_t *src = L"12345";
+  // These are all in the segment.
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"1"), size_t(0));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"2"), size_t(1));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"3"), size_t(2));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"4"), size_t(3));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"5"), size_t(4));
+}
+
+TEST(LlvmLibcWCSCSpnTest, UnmatchedCharacterShouldReturnLength) {
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"a", L"b"), size_t(1));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"abcdef", L"1"), size_t(6));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"123", L"4"), size_t(3));
+}
+
+TEST(LlvmLibcWCSCSpnTest, NonSequentialCharactersShouldNotSpan) {
+  const wchar_t *src = L"abc456789";
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"_1_abc_2_def_3_"), size_t(0));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(src, L"67__34xyz12"), size_t(3));
+}
+
+TEST(LlvmLibcWCSCSpnTest, ReverseCharacters) {
+  // These are all in the string.
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"12345", L"54321"), size_t(0));
+  // 1 is not in the span.
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"12345", L"432"), size_t(1));
+  // 1 is in the span.
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"12345", L"51"), size_t(0));
+}
+
+TEST(LlvmLibcWCSCSpnTest, DuplicatedCharactersToBeSearchedForShouldStillMatch) {
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"a", L"aa"), size_t(0));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"aa", L"aa"), size_t(0));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"aaa", L"bb"), size_t(3));
+  EXPECT_EQ(LIBC_NAMESPACE::wcscspn(L"aaaa", L"bb"), size_t(4));
+}