[libc-commits] [libc] [libc] wcsstr implementation (PR #142440)

[Michael Jones via libc-commits]

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@@ -0,0 +1,39 @@
+//===-- Implementation of wcsstr ------------------------------------------===//
+//
+// 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/wcsstr.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/string/string_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(const wchar_t *, wcsstr,
+                   (const wchar_t *s1, const wchar_t *s2)) {
+  size_t s1_len = internal::string_length(s1);
+  size_t s2_len = internal::string_length(s2);
+  // If string to be found has length 0, return s1.
+  if (s2_len == 0)
+    return s1;
+  // If string to be found has length longer than s1, return nullptr.
+  if (s2_len > s1_len)
+    return nullptr;
+  for (size_t i = 0; i <= (s1_len - s2_len); ++i) {
+    size_t j = 0;
+    for (; j < s2_len && s1[i + j] == s2[j]; ++j)
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michaelrj-google wrote:

nit: add a comment explaining this line, there's a lot going on.

https://github.com/llvm/llvm-project/pull/142440