[libc] wmemcmp implementation

Author: Sriya Pratipati

libc/config/linux/x86_64/entrypoints.txt

@@ -365,6 +365,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.wchar.wcslen
     libc.src.wchar.wctob
     libc.src.wchar.wcschr
+    libc.src.wchar.wmemcmp
 
     # sys/uio.h entrypoints
     libc.src.sys.uio.writev

libc/include/wchar.yaml

@@ -34,3 +34,11 @@ functions:
     arguments: 
       - type: const wchar_t *
       - type: wchar_t
+  - name: wmemcmp
+    standards:
+      - stdc
+    return_type: int
+    arguments: 
+      - type: const wchar_t *
+      - type: const wchar_t *
+      - type: size_t

libc/src/wchar/CMakeLists.txt

@@ -44,3 +44,15 @@ add_entrypoint_object(
     libc.hdr.wchar_macros
     libc.src.__support.wctype_utils
 )
+
+add_entrypoint_object(
+  wmemcmp
+  SRCS
+    wmemcmp.cpp
+  HDRS
+    wmemcmp.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.wchar_macros
+    libc.src.__support.wctype_utils
+)

libc/src/wchar/wmemcmp.cpp

@@ -0,0 +1,28 @@
+//===-- Implementation of wmemcmp ------------------------------------------===//
+//
+// 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/wmemcmp.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(int, wmemcmp,
+                   (const wchar_t *s1, const wchar_t *s2, size_t n)) {
+  for (size_t i = 0; i < n; ++s1, ++s2, ++i) {
+    if (*s1 != *s2)
+      return (int)(*s1 - *s2);
+  }
+  // If it reaches the end, all n values must be the same.
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/wchar/wmemcmp.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for wmemcmp ----------------------------------===//
+//
+// 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_WMEMCMP_H
+#define LLVM_LIBC_SRC_WCHAR_WMEMCMP_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int wmemcmp(const wchar_t *s1, const wchar_t *s2, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_WMEMCMP_H

libc/test/src/wchar/CMakeLists.txt

@@ -42,3 +42,13 @@ add_libc_test(
   DEPENDS
     libc.src.wchar.wcschr
 )
+
+add_libc_test(
+  wmemcmp_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wmemcmp_test.cpp
+  DEPENDS
+    libc.src.wchar.wmemcmp
+)

libc/test/src/wchar/wmemcmp_test.cpp

@@ -0,0 +1,40 @@
+//===-- Unittests for wmemcmp ----------------------------------------------===//
+//
+// 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/wmemcmp.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWMemcmpTest, CmpZeroByte) {
+  // Comparing zero bytes should result in 0.
+  const wchar_t *lhs = L"ab";
+  const wchar_t *rhs = L"yz";
+  EXPECT_EQ(LIBC_NAMESPACE::wmemcmp(lhs, rhs, 0), 0);
+}
+
+TEST(LlvmLibcWMemcmpTest, LhsRhsAreTheSame) {
+  // Comparing strings of equal value should result in 0.
+  const wchar_t *lhs = L"ab";
+  const wchar_t *rhs = L"ab";
+  EXPECT_EQ(LIBC_NAMESPACE::wmemcmp(lhs, rhs, 2), 0);
+}
+
+TEST(LlvmLibcWMemcmpTest, LhsBeforeRhsLexically) {
+  // z after b, should result in a value less than 0.
+  const wchar_t *lhs = L"ab";
+  const wchar_t *rhs = L"az";
+  EXPECT_LT(LIBC_NAMESPACE::wmemcmp(lhs, rhs, 2), 0);
+}
+
+TEST(LlvmLibcWMemcmpTest, LhsAfterRhsLexically) {
+  // z after b, should result in a value greater than 0.
+  const wchar_t *lhs = L"az";
+  const wchar_t *rhs = L"ab";
+  EXPECT_GT(LIBC_NAMESPACE::wmemcmp(lhs, rhs, 2), 0);
+}