ladybird/AK/Utf8View.cpp
Timothy Flynn 1d5b45f7d9 AK: Compute UTF-8 code point lengths using only leading bytes
We don't need to decode the entire code point to know its length. This
reduces the runtime of decoding a string containing 5 million instances
of U+10FFFF from over 4 seconds to 0.9 seconds.
2023-03-13 15:16:02 +00:00

248 lines
7.8 KiB
C++

/*
* Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
* Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Assertions.h>
#include <AK/Debug.h>
#include <AK/Format.h>
#include <AK/Utf8View.h>
namespace AK {
Utf8CodePointIterator Utf8View::iterator_at_byte_offset(size_t byte_offset) const
{
size_t current_offset = 0;
for (auto iterator = begin(); !iterator.done(); ++iterator) {
if (current_offset >= byte_offset)
return iterator;
current_offset += iterator.underlying_code_point_length_in_bytes();
}
return end();
}
Utf8CodePointIterator Utf8View::iterator_at_byte_offset_without_validation(size_t byte_offset) const
{
return Utf8CodePointIterator { reinterpret_cast<u8 const*>(m_string.characters_without_null_termination()) + byte_offset, m_string.length() - byte_offset };
}
size_t Utf8View::byte_offset_of(Utf8CodePointIterator const& it) const
{
VERIFY(it.m_ptr >= begin_ptr());
VERIFY(it.m_ptr <= end_ptr());
return it.m_ptr - begin_ptr();
}
size_t Utf8View::byte_offset_of(size_t code_point_offset) const
{
size_t byte_offset = 0;
for (auto it = begin(); !it.done(); ++it) {
if (code_point_offset == 0)
return byte_offset;
byte_offset += it.underlying_code_point_length_in_bytes();
--code_point_offset;
}
return byte_offset;
}
Utf8View Utf8View::unicode_substring_view(size_t code_point_offset, size_t code_point_length) const
{
if (code_point_length == 0)
return {};
size_t code_point_index = 0, offset_in_bytes = 0;
for (auto iterator = begin(); !iterator.done(); ++iterator) {
if (code_point_index == code_point_offset)
offset_in_bytes = byte_offset_of(iterator);
if (code_point_index == code_point_offset + code_point_length - 1) {
size_t length_in_bytes = byte_offset_of(++iterator) - offset_in_bytes;
return substring_view(offset_in_bytes, length_in_bytes);
}
++code_point_index;
}
VERIFY_NOT_REACHED();
}
size_t Utf8View::calculate_length() const
{
size_t length = 0;
for (size_t i = 0; i < m_string.length(); ++length) {
auto [byte_length, code_point, is_valid] = decode_leading_byte(static_cast<u8>(m_string[i]));
// Similar to Utf8CodePointIterator::operator++, if the byte is invalid, try the next byte.
i += is_valid ? byte_length : 1;
}
return length;
}
bool Utf8View::starts_with(Utf8View const& start) const
{
if (start.is_empty())
return true;
if (is_empty())
return false;
if (start.length() > length())
return false;
if (begin_ptr() == start.begin_ptr())
return true;
for (auto k = begin(), l = start.begin(); l != start.end(); ++k, ++l) {
if (*k != *l)
return false;
}
return true;
}
bool Utf8View::contains(u32 needle) const
{
for (u32 code_point : *this) {
if (code_point == needle)
return true;
}
return false;
}
Utf8View Utf8View::trim(Utf8View const& characters, TrimMode mode) const
{
size_t substring_start = 0;
size_t substring_length = byte_length();
if (mode == TrimMode::Left || mode == TrimMode::Both) {
for (auto code_point = begin(); code_point != end(); ++code_point) {
if (substring_length == 0)
return {};
if (!characters.contains(*code_point))
break;
substring_start += code_point.underlying_code_point_length_in_bytes();
substring_length -= code_point.underlying_code_point_length_in_bytes();
}
}
if (mode == TrimMode::Right || mode == TrimMode::Both) {
size_t seen_whitespace_length = 0;
for (auto code_point = begin(); code_point != end(); ++code_point) {
if (characters.contains(*code_point))
seen_whitespace_length += code_point.underlying_code_point_length_in_bytes();
else
seen_whitespace_length = 0;
}
if (seen_whitespace_length >= substring_length)
return {};
substring_length -= seen_whitespace_length;
}
return substring_view(substring_start, substring_length);
}
Utf8CodePointIterator& Utf8CodePointIterator::operator++()
{
VERIFY(m_length > 0);
size_t code_point_length_in_bytes = underlying_code_point_length_in_bytes();
if (code_point_length_in_bytes > m_length) {
// We don't have enough data for the next code point. Skip one character and try again.
// The rest of the code will output replacement characters as needed for any eventual extension bytes we might encounter afterwards.
dbgln_if(UTF8_DEBUG, "Expected code point size {} is too big for the remaining length {}. Moving forward one byte.", code_point_length_in_bytes, m_length);
m_ptr += 1;
m_length -= 1;
return *this;
}
m_ptr += code_point_length_in_bytes;
m_length -= code_point_length_in_bytes;
return *this;
}
size_t Utf8CodePointIterator::underlying_code_point_length_in_bytes() const
{
VERIFY(m_length > 0);
auto [code_point_length_in_bytes, value, first_byte_makes_sense] = Utf8View::decode_leading_byte(*m_ptr);
// If any of these tests fail, we will output a replacement character for this byte and treat it as a code point of size 1.
if (!first_byte_makes_sense)
return 1;
if (code_point_length_in_bytes > m_length)
return 1;
for (size_t offset = 1; offset < code_point_length_in_bytes; offset++) {
if (m_ptr[offset] >> 6 != 2)
return 1;
}
return code_point_length_in_bytes;
}
ReadonlyBytes Utf8CodePointIterator::underlying_code_point_bytes() const
{
return { m_ptr, underlying_code_point_length_in_bytes() };
}
u32 Utf8CodePointIterator::operator*() const
{
VERIFY(m_length > 0);
auto [code_point_length_in_bytes, code_point_value_so_far, first_byte_makes_sense] = Utf8View::decode_leading_byte(*m_ptr);
if (!first_byte_makes_sense) {
// The first byte of the code point doesn't make sense: output a replacement character
dbgln_if(UTF8_DEBUG, "First byte doesn't make sense: {:#02x}.", m_ptr[0]);
return 0xFFFD;
}
if (code_point_length_in_bytes > m_length) {
// There is not enough data left for the full code point: output a replacement character
dbgln_if(UTF8_DEBUG, "Not enough bytes (need {}, have {}), first byte is: {:#02x}.", code_point_length_in_bytes, m_length, m_ptr[0]);
return 0xFFFD;
}
for (size_t offset = 1; offset < code_point_length_in_bytes; offset++) {
if (m_ptr[offset] >> 6 != 2) {
// One of the extension bytes of the code point doesn't make sense: output a replacement character
dbgln_if(UTF8_DEBUG, "Extension byte {:#02x} in {} position after first byte {:#02x} doesn't make sense.", m_ptr[offset], offset, m_ptr[0]);
return 0xFFFD;
}
code_point_value_so_far <<= 6;
code_point_value_so_far |= m_ptr[offset] & 63;
}
if (code_point_value_so_far > 0x10FFFF) {
dbgln_if(UTF8_DEBUG, "Multi-byte sequence is otherwise valid, but code point {:#x} is not permissible.", code_point_value_so_far);
return 0xFFFD;
}
return code_point_value_so_far;
}
Optional<u32> Utf8CodePointIterator::peek(size_t offset) const
{
if (offset == 0) {
if (this->done())
return {};
return this->operator*();
}
auto new_iterator = *this;
for (size_t index = 0; index < offset; ++index) {
++new_iterator;
if (new_iterator.done())
return {};
}
return *new_iterator;
}
ErrorOr<void> Formatter<Utf8View>::format(FormatBuilder& builder, Utf8View const& string)
{
return Formatter<StringView>::format(builder, string.as_string());
}
}