[libc] Implemented wcsnlen (#145610)

Implemented wcsnlen and tests for the function.

---------

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

libc/config/linux/x86_64/entrypoints.txt

@@ -366,6 +366,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     # wchar.h entrypoints
     libc.src.wchar.btowc
     libc.src.wchar.wcslen
+    libc.src.wchar.wcsnlen
     libc.src.wchar.wctob
     libc.src.wchar.wmemmove
     libc.src.wchar.wmemset

libc/include/wchar.yaml

@@ -17,6 +17,13 @@ functions:
     return_type: size_t
     arguments:
       - type: const wchar_t *
+  - name: wcsnlen
+    standards:
+      - stdc
+    return_type: size_t
+    arguments:
+      - type: const wchar_t *
+      - type: size_t
   - name: wctob
     standards:
       - stdc

libc/src/wchar/CMakeLists.txt

@@ -10,6 +10,17 @@ add_entrypoint_object(
     libc.src.string.string_utils
 )
 
+add_entrypoint_object(
+  wcsnlen
+  SRCS
+    wcsnlen.cpp
+  HDRS
+    wcsnlen.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.wchar_t
+)
+
 add_entrypoint_object(
   wctob
   SRCS

libc/src/wchar/wcsnlen.cpp

@@ -0,0 +1,25 @@
+//===-- Implementation of wcsnlen -----------------------------------------===//
+//
+// 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/wcsnlen.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, wcsnlen, (const wchar_t *src, size_t maxlen)) {
+  size_t i = 0;
+  for (; i < maxlen && src[i]; ++i)
+    ;
+  return i;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/wchar/wcsnlen.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for wcsnlen ---------------------------------===//
+//
+// 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_WCSNLEN_H
+#define LLVM_LIBC_SRC_WCHAR_WCSNLEN_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t wcsnlen(const wchar_t *src, size_t maxlen);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_WCSNLEN_H

libc/test/src/wchar/CMakeLists.txt

@@ -12,6 +12,18 @@ add_libc_test(
     libc.src.wchar.wcslen
 )
 
+add_libc_test(
+  wcsnlen_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wcsnlen_test.cpp
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.wchar_t
+    libc.src.wchar.wcsnlen
+)
+
 add_libc_test(
   btowc_test
   SUITE

libc/test/src/wchar/wcsnlen_test.cpp

@@ -0,0 +1,54 @@
+//===-- Unittests for wcsnlen ---------------------------------------------===//
+//
+// 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/wcsnlen.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWCSNLenTest, EmptyString) {
+  ASSERT_EQ(static_cast<size_t>(0), LIBC_NAMESPACE::wcsnlen(L"", 0));
+  // If N is greater than string length, this should still return 0.
+  ASSERT_EQ(static_cast<size_t>(0), LIBC_NAMESPACE::wcsnlen(L"", 1));
+}
+
+TEST(LlvmLibcWCSNLenTest, OneCharacterString) {
+  const wchar_t *src = L"A";
+  ASSERT_EQ(static_cast<size_t>(1), LIBC_NAMESPACE::wcsnlen(src, 1));
+  // If N is 0, this should return 0.
+  ASSERT_EQ(static_cast<size_t>(0), LIBC_NAMESPACE::wcsnlen(src, 0));
+  // If N is greater than string length, this should still return 1.
+  ASSERT_EQ(static_cast<size_t>(1), LIBC_NAMESPACE::wcsnlen(src, 3));
+}
+
+TEST(LlvmLibcWCSNLenTest, ManyCharacterString) {
+  const wchar_t *src = L"123456789";
+  ASSERT_EQ(static_cast<size_t>(9), LIBC_NAMESPACE::wcsnlen(src, 9));
+  // If N is 0, this should return 0.
+  ASSERT_EQ(static_cast<size_t>(0), LIBC_NAMESPACE::wcsnlen(src, 0));
+  // If N is smaller than the string length, it should return N.
+  ASSERT_EQ(static_cast<size_t>(3), LIBC_NAMESPACE::wcsnlen(src, 3));
+  // If N is greater than string length, this should still return 9.
+  ASSERT_EQ(static_cast<size_t>(9), LIBC_NAMESPACE::wcsnlen(src, 42));
+}
+
+TEST(LlvmLibcWCSNLenTest, IgnoreCharactersAfterNullTerminator) {
+  const wchar_t src[5] = {L'a', L'b', L'c', L'\0', L'd'};
+  ASSERT_EQ(static_cast<size_t>(3), LIBC_NAMESPACE::wcsnlen(src, 3));
+  // This should only read up to the null terminator.
+  ASSERT_EQ(static_cast<size_t>(3), LIBC_NAMESPACE::wcsnlen(src, 4));
+  ASSERT_EQ(static_cast<size_t>(3), LIBC_NAMESPACE::wcsnlen(src, 5));
+}
+
+TEST(LlvmLibcWCSNLenTest, NoNullTerminator) {
+  const wchar_t src[4] = {L'a', L'b', L'c', L'd'};
+  // Should return 4
+  ASSERT_EQ(static_cast<size_t>(4), LIBC_NAMESPACE::wcsnlen(src, 4));
+  // Should return 2 since N is smaller than string length
+  ASSERT_EQ(static_cast<size_t>(2), LIBC_NAMESPACE::wcsnlen(src, 2));
+}