AK: Add String{View,}::find(StringView)

I personally mistook `find_first_of(StringView)` to be analogous to this
so let's add a `find()` method that actually searches the string.

AK/MemMem.h

@@ -120,28 +120,39 @@ static inline Optional<size_t> memmem(const HaystackIterT& haystack_begin, const
     return {};
 }
 
-static inline const void* memmem(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
+static inline Optional<size_t> memmem_optional(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
 {
     if (needle_length == 0)
-        return haystack;
+        return 0;
 
     if (haystack_length < needle_length)
-        return nullptr;
+        return {};
 
-    if (haystack_length == needle_length)
-        return __builtin_memcmp(haystack, needle, haystack_length) == 0 ? haystack : nullptr;
+    if (haystack_length == needle_length) {
+        if (__builtin_memcmp(haystack, needle, haystack_length) == 0)
+            return 0;
+        return {};
+    }
 
-    if (needle_length < 32)
-        return bitap_bitwise(haystack, haystack_length, needle, needle_length);
+    if (needle_length < 32) {
+        auto ptr = bitap_bitwise(haystack, haystack_length, needle, needle_length);
+        if (ptr)
+            return static_cast<size_t>((FlatPtr)ptr - (FlatPtr)haystack);
+        return {};
+    }
 
     // Fallback to KMP.
     Array<Span<const u8>, 1> spans { Span<const u8> { (const u8*)haystack, haystack_length } };
-    auto result = memmem(spans.begin(), spans.end(), { (const u8*)needle, needle_length });
+    return memmem(spans.begin(), spans.end(), { (const u8*)needle, needle_length });
+}
 
-    if (result.has_value())
-        return (const u8*)haystack + result.value();
+static inline const void* memmem(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
+{
+    auto offset = memmem_optional(haystack, haystack_length, needle, needle_length);
+    if (offset.has_value())
+        return ((const u8*)haystack) + offset.value();
 
-    return {};
+    return nullptr;
 }
 
 }

AK/String.cpp

@@ -469,4 +469,14 @@ String String::vformatted(StringView fmtstr, TypeErasedFormatParams params)
     return builder.to_string();
 }
 
+Optional<size_t> String::find(char c) const
+{
+    return find(StringView { &c, 1 });
+}
+
+Optional<size_t> String::find(const StringView& view) const
+{
+    return StringUtils::find(*this, view);
+}
+
 }

AK/String.h

@@ -138,6 +138,10 @@ public:
 
     Vector<String> split_limit(char separator, size_t limit, bool keep_empty = false) const;
     Vector<String> split(char separator, bool keep_empty = false) const;
+
+    Optional<size_t> find(char) const;
+    Optional<size_t> find(const StringView&) const;
+
     String substring(size_t start) const;
     String substring(size_t start, size_t length) const;
 

AK/StringUtils.cpp

@@ -25,6 +25,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/MemMem.h>
 #include <AK/Memory.h>
 #include <AK/Optional.h>
 #include <AK/String.h>
@@ -342,6 +343,13 @@ StringView trim_whitespace(const StringView& str, TrimMode mode)
 
     return str.substring_view(substring_start, substring_length);
 }
+
+Optional<size_t> find(const StringView& haystack, const StringView& needle)
+{
+    return AK::memmem_optional(
+        haystack.characters_without_null_termination(), haystack.length(),
+        needle.characters_without_null_termination(), needle.length());
+}
 }
 
 }

AK/StringUtils.h

@@ -71,6 +71,7 @@ bool starts_with(const StringView&, const StringView&, CaseSensitivity);
 bool contains(const StringView&, const StringView&, CaseSensitivity);
 bool is_whitespace(const StringView&);
 StringView trim_whitespace(const StringView&, TrimMode mode);
+Optional<size_t> find(const StringView& haystack, const StringView& needle);
 }
 
 }

AK/StringView.cpp

@@ -310,6 +310,16 @@ Optional<size_t> StringView::find_last_of(const StringView& view) const
     return {};
 }
 
+Optional<size_t> StringView::find(char c) const
+{
+    return find(StringView { &c, 1 });
+}
+
+Optional<size_t> StringView::find(const StringView& view) const
+{
+    return StringUtils::find(*this, view);
+}
+
 String StringView::to_string() const { return String { *this }; }
 
 }

AK/StringView.h

@@ -100,6 +100,9 @@ public:
     Optional<size_t> find_last_of(char) const;
     Optional<size_t> find_last_of(const StringView&) const;
 
+    Optional<size_t> find(const StringView&) const;
+    Optional<size_t> find(char c) const;
+
     StringView substring_view(size_t start, size_t length) const;
     StringView substring_view(size_t start) const;
     Vector<StringView> split_view(char, bool keep_empty = false) const;

AK/Tests/TestStringUtils.cpp

@@ -298,4 +298,16 @@ TEST_CASE(is_whitespace)
     EXPECT(!AK::StringUtils::is_whitespace("a\t"));
 }
 
+TEST_CASE(find)
+{
+    String test_string = "1234567";
+    EXPECT_EQ(AK::StringUtils::find(test_string, "1").value_or(1), 0u);
+    EXPECT_EQ(AK::StringUtils::find(test_string, "2").value_or(2), 1u);
+    EXPECT_EQ(AK::StringUtils::find(test_string, "3").value_or(3), 2u);
+    EXPECT_EQ(AK::StringUtils::find(test_string, "4").value_or(4), 3u);
+    EXPECT_EQ(AK::StringUtils::find(test_string, "5").value_or(5), 4u);
+    EXPECT_EQ(AK::StringUtils::find(test_string, "34").value_or(3), 2u);
+    EXPECT_EQ(AK::StringUtils::find(test_string, "78").has_value(), false);
+}
+
 TEST_MAIN(StringUtils)