[libc] Implemented wcsncmp (#142429)

Implemented wcsncmp and added tests

7 files changed, 258 insertions, 0 deletions

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index c883cb6..a30ffbe0b 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -366,6 +366,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.wchar.wctob
     libc.src.wchar.wmemset
     libc.src.wchar.wcschr
+    libc.src.wchar.wcsncmp
     libc.src.wchar.wcscmp
     libc.src.wchar.wcspbrk
     libc.src.wchar.wcsrchr
diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 2eaefbf..29a989f 100644
--- a/libc/include/wchar.yaml
+++ b/libc/include/wchar.yaml
@@ -42,6 +42,14 @@ functions:
     arguments: 
       - type: const wchar_t *
       - type: wchar_t
+  - name: wcsncmp
+  standards:
+      - stdc
+    return_type: int
+    arguments:
+      - type: const wchar_t *
+      - type: const wchar_t *
+      - type: size_t
   - name: wcscmp
     standards:
       - stdc
diff --git a/libc/src/wchar/CMakeLists.txt b/libc/src/wchar/CMakeLists.txt
index 17b5500..be62495 100644
--- a/libc/src/wchar/CMakeLists.txt
+++ b/libc/src/wchar/CMakeLists.txt
@@ -90,6 +90,17 @@ add_entrypoint_object(
 )
 
 add_entrypoint_object(
+  wcsncmp
+  SRCS
+    wcsncmp.cpp
+  HDRS
+    wcsncmp.h
+  DEPENDS
+    libc.hdr.wchar_macros
+    libc.hdr.types.size_t
+)
+
+add_entrypoint_object(
   wcsspn
   SRCS
     wcsspn.cpp
diff --git a/libc/src/wchar/wcsncmp.cpp b/libc/src/wchar/wcsncmp.cpp
new file mode 100644
index 0000000..f2e052b
--- /dev/null
+++ b/libc/src/wchar/wcsncmp.cpp
@@ -0,0 +1,37 @@
+//===-- Implementation of wcsncmp -----------------------------------------===//
+//
+// 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/wcsncmp.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/null_check.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, wcsncmp,
+                   (const wchar_t *left, const wchar_t *right, size_t n)) {
+  LIBC_CRASH_ON_NULLPTR(left);
+  LIBC_CRASH_ON_NULLPTR(right);
+
+  if (n == 0)
+    return 0;
+
+  auto comp = [](wchar_t l, wchar_t r) -> int { return l - r; };
+
+  for (; n > 1; --n, ++left, ++right) {
+    wchar_t lc = *left;
+    if (!comp(lc, '\0') || comp(lc, *right))
+      break;
+  }
+  return comp(*reinterpret_cast<const wchar_t *>(left),
+              *reinterpret_cast<const wchar_t *>(right));
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/wchar/wcsncmp.h b/libc/src/wchar/wcsncmp.h
new file mode 100644
index 0000000..0b4187e73
--- /dev/null
+++ b/libc/src/wchar/wcsncmp.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for wcsncmp ---------------------------------===//
+//
+// 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_WCSNCMP_H
+#define LLVM_LIBC_SRC_WCHAR_WCSNCMP_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int wcsncmp(const wchar_t *left, const wchar_t *right, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_WCSNCMP_H
diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index 7743b0f..38ff8b8 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/libc/test/src/wchar/CMakeLists.txt
@@ -56,6 +56,16 @@ add_libc_test(
 )
 
 add_libc_test(
+  wcsncmp_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wcsncmp_test.cpp
+  DEPENDS
+    libc.src.wchar.wcsncmp
+)
+
+add_libc_test(
   wcscmp_test
   SUITE
     libc_wchar_unittests
diff --git a/libc/test/src/wchar/wcsncmp_test.cpp b/libc/test/src/wchar/wcsncmp_test.cpp
new file mode 100644
index 0000000..28bbb52
--- /dev/null
+++ b/libc/test/src/wchar/wcsncmp_test.cpp
@@ -0,0 +1,169 @@
+//===-- Unittests for wcsncmp ---------------------------------------------===//
+//
+// 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/wcsncmp.h"
+#include "test/UnitTest/Test.h"
+
+// This group is just copies of the wcscmp tests, since all the same cases still
+// need to be tested.
+
+TEST(LlvmLibcWcsncmpTest, EmptyStringsShouldReturnZeroWithSufficientLength) {
+  const wchar_t *s1 = L"";
+  const wchar_t *s2 = L"";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 1);
+  ASSERT_EQ(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 1);
+  ASSERT_EQ(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest,
+     EmptyStringShouldNotEqualNonEmptyStringWithSufficientLength) {
+  const wchar_t *empty = L"";
+  const wchar_t *s2 = L"abc";
+  int result = LIBC_NAMESPACE::wcsncmp(empty, s2, 3);
+  ASSERT_LT(result, 0);
+
+  // Similar case if empty string is second argument.
+  const wchar_t *s3 = L"123";
+  result = LIBC_NAMESPACE::wcsncmp(s3, empty, 3);
+  ASSERT_GT(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest, EqualStringsShouldReturnZeroWithSufficientLength) {
+  const wchar_t *s1 = L"abc";
+  const wchar_t *s2 = L"abc";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 3);
+  ASSERT_EQ(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 3);
+  ASSERT_EQ(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest,
+     ShouldReturnResultOfFirstDifferenceWithSufficientLength) {
+  const wchar_t *s1 = L"___B42__";
+  const wchar_t *s2 = L"___C55__";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 8);
+  ASSERT_LT(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 8);
+  ASSERT_GT(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest,
+     CapitalizedLetterShouldNotBeEqualWithSufficientLength) {
+  const wchar_t *s1 = L"abcd";
+  const wchar_t *s2 = L"abCd";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 4);
+  ASSERT_GT(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 4);
+  ASSERT_LT(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest,
+     UnequalLengthStringsShouldNotReturnZeroWithSufficientLength) {
+  const wchar_t *s1 = L"abc";
+  const wchar_t *s2 = L"abcd";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 4);
+  ASSERT_LT(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 4);
+  ASSERT_GT(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest, StringArgumentSwapChangesSignWithSufficientLength) {
+  const wchar_t *a = L"a";
+  const wchar_t *b = L"b";
+  int result = LIBC_NAMESPACE::wcsncmp(b, a, 1);
+  ASSERT_GT(result, 0);
+
+  result = LIBC_NAMESPACE::wcsncmp(a, b, 1);
+  ASSERT_LT(result, 0);
+}
+
+#if defined(LIBC_ADD_NULL_CHECKS) && !defined(LIBC_HAS_SANITIZER)
+TEST(LlvmLibcWcsncmpTest, NullptrCrash) {
+  // Passing in a nullptr should crash the program.
+  EXPECT_DEATH([] { LIBC_NAMESPACE::wcsncmp(L"aaaaaaaaaaaaaa", nullptr, 3); },
+               WITH_SIGNAL(-1));
+  EXPECT_DEATH([] { LIBC_NAMESPACE::wcsncmp(nullptr, L"aaaaaaaaaaaaaa", 3); },
+               WITH_SIGNAL(-1));
+}
+#endif // LIBC_HAS_ADDRESS_SANITIZER
+
+// This group is actually testing wcsncmp functionality
+
+TEST(LlvmLibcWcsncmpTest, NonEqualStringsEqualWithLengthZero) {
+  const wchar_t *s1 = L"abc";
+  const wchar_t *s2 = L"def";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 0);
+  ASSERT_EQ(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 0);
+  ASSERT_EQ(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest, NonEqualStringsNotEqualWithLengthOne) {
+  const wchar_t *s1 = L"abc";
+  const wchar_t *s2 = L"def";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 1);
+  ASSERT_LT(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 1);
+  ASSERT_GT(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest, NonEqualStringsEqualWithShorterLength) {
+  const wchar_t *s1 = L"___B42__";
+  const wchar_t *s2 = L"___C55__";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 3);
+  ASSERT_EQ(result, 0);
+
+  // This should return 'B' - 'C' = -1.
+  result = LIBC_NAMESPACE::wcsncmp(s1, s2, 4);
+  ASSERT_LT(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 3);
+  ASSERT_EQ(result, 0);
+
+  // This should return 'C' - 'B' = 1.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 4);
+  ASSERT_GT(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest, StringComparisonEndsOnNullByteEvenWithLongerLength) {
+  const wchar_t *s1 = L"abc\0def";
+  const wchar_t *s2 = L"abc\0abc";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 7);
+  ASSERT_EQ(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 7);
+  ASSERT_EQ(result, 0);
+}
+
+TEST(LlvmLibcWcsncmpTest, Case) {
+  const wchar_t *s1 = L"aB";
+  const wchar_t *s2 = L"ab";
+  int result = LIBC_NAMESPACE::wcsncmp(s1, s2, 2);
+  ASSERT_LT(result, 0);
+
+  // Verify operands reversed.
+  result = LIBC_NAMESPACE::wcsncmp(s2, s1, 2);
+  ASSERT_GT(result, 0);
+}