AK+LibTextCodec: Stop using Utf16View endianness override

This is preparation for removing the endianness override, since it was
only used by a single client: LibTextCodec.

While here, add helpers and make use of simdutf for fast conversion.

AK/String.cpp

@@ -61,6 +61,36 @@ ErrorOr<String> String::from_utf8(StringView view)
     return result;
 }
 
+ErrorOr<String> String::from_utf16_le(ReadonlyBytes bytes)
+{
+    if (!validate_utf16_le(bytes))
+        return Error::from_string_literal("String::from_utf16_le: Input was not valid UTF-16LE");
+    if (bytes.is_empty())
+        return String {};
+    char16_t const* utf16_data = reinterpret_cast<char16_t const*>(bytes.data());
+    size_t utf16_length = bytes.size() / 2;
+    size_t max_utf8_length = simdutf::utf8_length_from_utf16(utf16_data, utf16_length);
+    Vector<u8> buffer;
+    buffer.resize(max_utf8_length);
+    auto utf8_length = simdutf::convert_utf16le_to_utf8(utf16_data, utf16_length, reinterpret_cast<char*>(buffer.data()));
+    return String::from_utf8_without_validation(ReadonlyBytes { buffer.data(), utf8_length });
+}
+
+ErrorOr<String> String::from_utf16_be(ReadonlyBytes bytes)
+{
+    if (!validate_utf16_be(bytes))
+        return Error::from_string_literal("String::from_utf16_be: Input was not valid UTF-16BE");
+    if (bytes.is_empty())
+        return String {};
+    char16_t const* utf16_data = reinterpret_cast<char16_t const*>(bytes.data());
+    size_t utf16_length = bytes.size() / 2;
+    size_t max_utf8_length = simdutf::utf8_length_from_utf16(utf16_data, utf16_length);
+    Vector<u8> buffer;
+    buffer.resize(max_utf8_length);
+    auto utf8_length = simdutf::convert_utf16be_to_utf8(utf16_data, utf16_length, reinterpret_cast<char*>(buffer.data()));
+    return String::from_utf8_without_validation(ReadonlyBytes { buffer.data(), utf8_length });
+}
+
 ErrorOr<String> String::from_utf16(Utf16View const& utf16)
 {
     if (!utf16.validate())

AK/String.h

@@ -70,6 +70,8 @@ public:
 
     // Creates a new String from a sequence of UTF-16 encoded code points.
     static ErrorOr<String> from_utf16(Utf16View const&);
+    static ErrorOr<String> from_utf16_le(ReadonlyBytes);
+    static ErrorOr<String> from_utf16_be(ReadonlyBytes);
 
     // Creates a new String by reading byte_count bytes from a UTF-8 encoded Stream.
     static ErrorOr<String> from_stream(Stream&, size_t byte_count);

AK/Utf16View.cpp

@@ -421,4 +421,14 @@ size_t Utf16CodePointIterator::length_in_code_units() const
     return *(*this) < first_supplementary_plane_code_point ? 1 : 2;
 }
 
+bool validate_utf16_le(ReadonlyBytes bytes)
+{
+    return simdutf::validate_utf16le(reinterpret_cast<char16_t const*>(bytes.data()), bytes.size() / 2);
+}
+
+bool validate_utf16_be(ReadonlyBytes bytes)
+{
+    return simdutf::validate_utf16be(reinterpret_cast<char16_t const*>(bytes.data()), bytes.size() / 2);
+}
+
 }

AK/Utf16View.h

@@ -26,6 +26,9 @@ ErrorOr<Utf16Data> utf8_to_utf16(Utf8View const&, Endianness = Endianness::Host)
 ErrorOr<Utf16Data> utf32_to_utf16(Utf32View const&, Endianness = Endianness::Host);
 ErrorOr<void> code_point_to_utf16(Utf16Data&, u32, Endianness = Endianness::Host);
 
+[[nodiscard]] bool validate_utf16_le(ReadonlyBytes);
+[[nodiscard]] bool validate_utf16_be(ReadonlyBytes);
+
 size_t utf16_code_unit_length_from_utf8(StringView);
 
 class Utf16View;

Libraries/LibTextCodec/Decoder.cpp

@@ -369,25 +369,9 @@ ErrorOr<String> UTF8Decoder::to_utf8(StringView input)
     return String::from_utf8_with_replacement_character(input);
 }
 
-static Utf16View as_utf16(StringView view, AK::Endianness endianness)
-{
-    return Utf16View {
-        { reinterpret_cast<u16 const*>(view.bytes().data()), view.length() / 2 },
-        endianness
-    };
-}
-
-ErrorOr<void> UTF16BEDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
-{
-    for (auto code_point : as_utf16(input, AK::Endianness::Big))
-        TRY(on_code_point(code_point));
-
-    return {};
-}
-
 bool UTF16BEDecoder::validate(StringView input)
 {
-    return as_utf16(input, AK::Endianness::Big).validate();
+    return AK::validate_utf16_be(input.bytes());
 }
 
 ErrorOr<String> UTF16BEDecoder::to_utf8(StringView input)
@@ -396,20 +380,12 @@ ErrorOr<String> UTF16BEDecoder::to_utf8(StringView input)
     if (auto bytes = input.bytes(); bytes.size() >= 2 && bytes[0] == 0xFE && bytes[1] == 0xFF)
         input = input.substring_view(2);
 
-    return String::from_utf16(as_utf16(input, AK::Endianness::Big));
-}
-
-ErrorOr<void> UTF16LEDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
-{
-    for (auto code_point : as_utf16(input, AK::Endianness::Little))
-        TRY(on_code_point(code_point));
-
-    return {};
+    return String::from_utf16_be(input.bytes());
 }
 
 bool UTF16LEDecoder::validate(StringView input)
 {
-    return as_utf16(input, AK::Endianness::Little).validate();
+    return AK::validate_utf16_le(input.bytes());
 }
 
 ErrorOr<String> UTF16LEDecoder::to_utf8(StringView input)
@@ -418,7 +394,7 @@ ErrorOr<String> UTF16LEDecoder::to_utf8(StringView input)
     if (auto bytes = input.bytes(); bytes.size() >= 2 && bytes[0] == 0xFF && bytes[1] == 0xFE)
         input = input.substring_view(2);
 
-    return String::from_utf16(as_utf16(input, AK::Endianness::Little));
+    return String::from_utf16_le(input.bytes());
 }
 
 ErrorOr<void> Latin1Decoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)

Libraries/LibTextCodec/Decoder.h

@@ -17,12 +17,12 @@ namespace TextCodec {
 
 class Decoder {
 public:
-    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) = 0;
     virtual bool validate(StringView);
     virtual ErrorOr<String> to_utf8(StringView);
 
 protected:
     virtual ~Decoder() = default;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) = 0;
 };
 
 class UTF8Decoder final : public Decoder {
@@ -34,16 +34,20 @@ public:
 
 class UTF16BEDecoder final : public Decoder {
 public:
-    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
     virtual bool validate(StringView) override;
     virtual ErrorOr<String> to_utf8(StringView) override;
+
+private:
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)>) override { VERIFY_NOT_REACHED(); }
 };
 
 class UTF16LEDecoder final : public Decoder {
 public:
-    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
     virtual bool validate(StringView) override;
     virtual ErrorOr<String> to_utf8(StringView) override;
+
+private:
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)>) override { VERIFY_NOT_REACHED(); }
 };
 
 template<Integral ArrayType = u32>

Tests/LibTextCodec/TestTextDecoders.cpp

@@ -34,17 +34,6 @@ TEST_CASE(test_utf16be_decode)
     auto test_string = "\x00s\x00\xe4\x00k\xd8=\xde\x00"sv;
 
     EXPECT(decoder.validate(test_string));
-
-    Vector<u32> processed_code_points;
-    MUST(decoder.process(test_string, [&](u32 code_point) {
-        return processed_code_points.try_append(code_point);
-    }));
-    EXPECT(processed_code_points.size() == 4);
-    EXPECT(processed_code_points[0] == 0x73);
-    EXPECT(processed_code_points[1] == 0xE4);
-    EXPECT(processed_code_points[2] == 0x6B);
-    EXPECT(processed_code_points[3] == 0x1F600);
-
     auto utf8 = MUST(decoder.to_utf8(test_string));
     EXPECT_EQ(utf8, "säk😀"sv);
 }
@@ -56,17 +45,6 @@ TEST_CASE(test_utf16le_decode)
     auto test_string = "s\x00\xe4\x00k\x00=\xd8\x00\xde"sv;
 
     EXPECT(decoder.validate(test_string));
-
-    Vector<u32> processed_code_points;
-    MUST(decoder.process(test_string, [&](u32 code_point) {
-        return processed_code_points.try_append(code_point);
-    }));
-    EXPECT(processed_code_points.size() == 4);
-    EXPECT(processed_code_points[0] == 0x73);
-    EXPECT(processed_code_points[1] == 0xE4);
-    EXPECT(processed_code_points[2] == 0x6B);
-    EXPECT(processed_code_points[3] == 0x1F600);
-
     auto utf8 = MUST(decoder.to_utf8(test_string));
     EXPECT_EQ(utf8, "säk😀"sv);
 }