fixed behavior for case with no null terminator

Author: Sriya Pratipati

libc/src/wchar/wcsnlen.cpp

@@ -17,8 +17,10 @@
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(size_t, wcsnlen, (const wchar_t *src, size_t maxlen)) {
-  size_t temp = internal::string_length(src);
-  return temp > maxlen ? maxlen : temp;
+  size_t i = 0;
+  for (; i < maxlen && src[i]; ++i)
+    ;
+  return i;
 }
 
 } // namespace LIBC_NAMESPACE_DECL

libc/test/src/wchar/wcsnlen_test.cpp

@@ -44,3 +44,11 @@ TEST(LlvmLibcWCSNLenTest, IgnoreCharactersAfterNullTerminator) {
   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));
+}