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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Create a state machine for validating UTF-8. The algorithm in brief:
// 1. Convert the complete unicode range of code points, except for the
// surrogate code points, to an ordered array of sequences of bytes in
// UTF-8.
// 2. Convert individual bytes to ranges, starting from the right of each byte
// sequence. For each range, ensure the bytes on the left and the ranges
// on the right are the identical.
// 3. Convert the resulting list of ranges into a state machine, collapsing
// identical states.
// 4. Convert the state machine to an array of bytes.
// 5. Output as a C++ file.
//
// To use:
// $ ninja -C out/Release build_utf8_validator_tables
// $ out/Release/build_utf8_validator_tables
// --output=base/i18n/utf8_validator_tables.cc
// $ git add base/i18n/utf8_validator_tables.cc
//
// Because the table is not expected to ever change, it is checked into the
// repository rather than being regenerated at build time.
//
// This code uses type uint8_t throughout to represent bytes, to avoid
// signed/unsigned char confusion.
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include <map>
#include <string>
#include <vector>
#include "base/command_line.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/numerics/safe_conversions.h"
#include "base/strings/stringprintf.h"
#include "third_party/icu/source/common/unicode/utf8.h"
namespace {
const char kHelpText[] =
"Usage: build_utf8_validator_tables [ --help ] [ --output=<file> ]\n";
const char kProlog[] =
"// Copyright 2013 The Chromium Authors. All rights reserved.\n"
"// Use of this source code is governed by a BSD-style license that can "
"be\n"
"// found in the LICENSE file.\n"
"\n"
"// This file is auto-generated by build_utf8_validator_tables.\n"
"// DO NOT EDIT.\n"
"\n"
"#include \"base/i18n/utf8_validator_tables.h\"\n"
"\n"
"namespace base {\n"
"namespace internal {\n"
"\n"
"const uint8_t kUtf8ValidatorTables[] = {\n";
const char kEpilog[] =
"};\n"
"\n"
"const size_t kUtf8ValidatorTablesSize = arraysize(kUtf8ValidatorTables);\n"
"\n"
"} // namespace internal\n"
"} // namespace base\n";
// Ranges are inclusive at both ends--they represent [from, to]
class Range {
public:
// Ranges always start with just one byte.
explicit Range(uint8_t value) : from_(value), to_(value) {}
// Range objects are copyable and assignable to be used in STL
// containers. Since they only contain non-pointer POD types, the default copy
// constructor, assignment operator and destructor will work.
// Add a byte to the range. We intentionally only support adding a byte at the
// end, since that is the only operation the code needs.
void AddByte(uint8_t to) {
CHECK(to == to_ + 1);
to_ = to;
}
uint8_t from() const { return from_; }
uint8_t to() const { return to_; }
bool operator<(const Range& rhs) const {
return (from() < rhs.from() || (from() == rhs.from() && to() < rhs.to()));
}
bool operator==(const Range& rhs) const {
return from() == rhs.from() && to() == rhs.to();
}
private:
uint8_t from_;
uint8_t to_;
};
// A vector of Ranges is like a simple regular expression--it corresponds to
// a set of strings of the same length that have bytes in each position in
// the appropriate range.
typedef std::vector<Range> StringSet;
// A UTF-8 "character" is represented by a sequence of bytes.
typedef std::vector<uint8_t> Character;
// In the second stage of the algorithm, we want to convert a large list of
// Characters into a small list of StringSets.
struct Pair {
Character character;
StringSet set;
};
typedef std::vector<Pair> PairVector;
// A class to print a table of numbers in the same style as clang-format.
class TablePrinter {
public:
explicit TablePrinter(FILE* stream)
: stream_(stream), values_on_this_line_(0), current_offset_(0) {}
void PrintValue(uint8_t value) {
if (values_on_this_line_ == 0) {
fputs(" ", stream_);
} else if (values_on_this_line_ == kMaxValuesPerLine) {
fprintf(stream_, " // 0x%02x\n ", current_offset_);
values_on_this_line_ = 0;
}
fprintf(stream_, " 0x%02x,", static_cast<int>(value));
++values_on_this_line_;
++current_offset_;
}
void NewLine() {
while (values_on_this_line_ < kMaxValuesPerLine) {
fputs(" ", stream_);
++values_on_this_line_;
}
fprintf(stream_, " // 0x%02x\n", current_offset_);
values_on_this_line_ = 0;
}
private:
// stdio stream. Not owned.
FILE* stream_;
// Number of values so far printed on this line.
int values_on_this_line_;
// Total values printed so far.
int current_offset_;
static const int kMaxValuesPerLine = 8;
DISALLOW_COPY_AND_ASSIGN(TablePrinter);
};
// Start by filling a PairVector with characters. The resulting vector goes from
// "\x00" to "\xf4\x8f\xbf\xbf".
PairVector InitializeCharacters() {
PairVector vector;
for (int i = 0; i <= 0x10FFFF; ++i) {
if (i >= 0xD800 && i < 0xE000) {
// Surrogate codepoints are not permitted. Non-character code points are
// explicitly permitted.
continue;
}
uint8_t bytes[4];
unsigned int offset = 0;
UBool is_error = false;
U8_APPEND(bytes, offset, arraysize(bytes), i, is_error);
DCHECK(!is_error);
DCHECK_GT(offset, 0u);
DCHECK_LE(offset, arraysize(bytes));
Pair pair = {Character(bytes, bytes + offset), StringSet()};
vector.push_back(pair);
}
return vector;
}
// Construct a new Pair from |character| and the concatenation of |new_range|
// and |existing_set|, and append it to |pairs|.
void ConstructPairAndAppend(const Character& character,
const Range& new_range,
const StringSet& existing_set,
PairVector* pairs) {
Pair new_pair = {character, StringSet(1, new_range)};
new_pair.set.insert(
new_pair.set.end(), existing_set.begin(), existing_set.end());
pairs->push_back(new_pair);
}
// Each pass over the PairVector strips one byte off the right-hand-side of the
// characters and adds a range to the set on the right. For example, the first
// pass converts the range from "\xe0\xa0\x80" to "\xe0\xa0\xbf" to ("\xe0\xa0",
// [\x80-\xbf]), then the second pass converts the range from ("\xe0\xa0",
// [\x80-\xbf]) to ("\xe0\xbf", [\x80-\xbf]) to ("\xe0",
// [\xa0-\xbf][\x80-\xbf]).
void MoveRightMostCharToSet(PairVector* pairs) {
PairVector new_pairs;
PairVector::const_iterator it = pairs->begin();
while (it != pairs->end() && it->character.empty()) {
new_pairs.push_back(*it);
++it;
}
CHECK(it != pairs->end());
Character unconverted_bytes(it->character.begin(), it->character.end() - 1);
Range new_range(it->character.back());
StringSet converted = it->set;
++it;
while (it != pairs->end()) {
const Pair& current_pair = *it++;
if (current_pair.character.size() == unconverted_bytes.size() + 1 &&
std::equal(unconverted_bytes.begin(),
unconverted_bytes.end(),
current_pair.character.begin()) &&
converted == current_pair.set) {
// The particular set of UTF-8 codepoints we are validating guarantees
// that each byte range will be contiguous. This would not necessarily be
// true for an arbitrary set of UTF-8 codepoints.
DCHECK_EQ(new_range.to() + 1, current_pair.character.back());
new_range.AddByte(current_pair.character.back());
continue;
}
ConstructPairAndAppend(unconverted_bytes, new_range, converted, &new_pairs);
unconverted_bytes = Character(current_pair.character.begin(),
current_pair.character.end() - 1);
new_range = Range(current_pair.character.back());
converted = current_pair.set;
}
ConstructPairAndAppend(unconverted_bytes, new_range, converted, &new_pairs);
new_pairs.swap(*pairs);
}
void MoveAllCharsToSets(PairVector* pairs) {
// Since each pass of the function moves one character, and UTF-8 sequences
// are at most 4 characters long, this simply runs the algorithm four times.
for (int i = 0; i < 4; ++i) {
MoveRightMostCharToSet(pairs);
}
#if DCHECK_IS_ON()
for (PairVector::const_iterator it = pairs->begin(); it != pairs->end();
++it) {
DCHECK(it->character.empty());
}
#endif
}
// Logs the generated string sets in regular-expression style, ie. [\x00-\x7f],
// [\xc2-\xdf][\x80-\xbf], etc. This can be a useful sanity-check that the
// algorithm is working. Use the command-line option
// --vmodule=build_utf8_validator_tables=1 to see this output.
void LogStringSets(const PairVector& pairs) {
for (PairVector::const_iterator pair_it = pairs.begin();
pair_it != pairs.end();
++pair_it) {
std::string set_as_string;
for (StringSet::const_iterator set_it = pair_it->set.begin();
set_it != pair_it->set.end();
++set_it) {
set_as_string += base::StringPrintf("[\\x%02x-\\x%02x]",
static_cast<int>(set_it->from()),
static_cast<int>(set_it->to()));
}
VLOG(1) << set_as_string;
}
}
// A single state in the state machine is represented by a sorted vector of
// start bytes and target states. All input bytes in the range between the start
// byte and the next entry in the vector (or 0xFF) result in a transition to the
// target state.
struct StateRange {
uint8_t from;
uint8_t target_state;
};
typedef std::vector<StateRange> State;
// Generates a state where all bytes go to state 1 (invalid). This is also used
// as an initialiser for other states (since bytes from outside the desired
// range are invalid).
State GenerateInvalidState() {
const StateRange range = {0, 1};
return State(1, range);
}
// A map from a state (ie. a set of strings which will match from this state) to
// a number (which is an index into the array of states).
typedef std::map<StringSet, uint8_t> StateMap;
// Create a new state corresponding to |set|, add it |states| and |state_map|
// and return the index it was given in |states|.
uint8_t MakeState(const StringSet& set,
std::vector<State>* states,
StateMap* state_map) {
DCHECK(!set.empty());
const Range& range = set.front();
const StringSet rest(set.begin() + 1, set.end());
const StateMap::const_iterator where = state_map->find(rest);
const uint8_t target_state = where == state_map->end()
? MakeState(rest, states, state_map)
: where->second;
DCHECK_LT(0, range.from());
DCHECK_LT(range.to(), 0xFF);
const StateRange new_state_initializer[] = {
{0, 1},
{range.from(), target_state},
{static_cast<uint8_t>(range.to() + 1), 1}};
states->push_back(
State(new_state_initializer,
new_state_initializer + arraysize(new_state_initializer)));
const uint8_t new_state_number =
base::checked_cast<uint8_t>(states->size() - 1);
CHECK(state_map->insert(std::make_pair(set, new_state_number)).second);
return new_state_number;
}
std::vector<State> GenerateStates(const PairVector& pairs) {
// States 0 and 1 are the initial/valid state and invalid state, respectively.
std::vector<State> states(2, GenerateInvalidState());
StateMap state_map;
state_map.insert(std::make_pair(StringSet(), 0));
for (PairVector::const_iterator it = pairs.begin(); it != pairs.end(); ++it) {
DCHECK(it->character.empty());
DCHECK(!it->set.empty());
const Range& range = it->set.front();
const StringSet rest(it->set.begin() + 1, it->set.end());
const StateMap::const_iterator where = state_map.find(rest);
const uint8_t target_state = where == state_map.end()
? MakeState(rest, &states, &state_map)
: where->second;
if (states[0].back().from == range.from()) {
DCHECK_EQ(1, states[0].back().target_state);
states[0].back().target_state = target_state;
DCHECK_LT(range.to(), 0xFF);
const StateRange new_range = {static_cast<uint8_t>(range.to() + 1), 1};
states[0].push_back(new_range);
} else {
DCHECK_LT(range.to(), 0xFF);
const StateRange new_range_initializer[] = {
{range.from(), target_state},
{static_cast<uint8_t>(range.to() + 1), 1}};
states[0]
.insert(states[0].end(),
new_range_initializer,
new_range_initializer + arraysize(new_range_initializer));
}
}
return states;
}
// Output the generated states as a C++ table. Two tricks are used to compact
// the table: each state in the table starts with a shift value which indicates
// how many bits we can discard from the right-hand-side of the byte before
// doing the table lookup. Secondly, only the state-transitions for bytes
// with the top-bit set are included in the table; bytes without the top-bit set
// are just ASCII and are handled directly by the code.
void PrintStates(const std::vector<State>& states, FILE* stream) {
// First calculate the start-offset of each state. This allows the state
// machine to jump directly to the correct offset, avoiding an extra
// indirection. State 0 starts at offset 0.
std::vector<uint8_t> state_offset(1, 0);
std::vector<uint8_t> shifts;
uint8_t pos = 0;
for (std::vector<State>::const_iterator state_it = states.begin();
state_it != states.end();
++state_it) {
// We want to set |shift| to the (0-based) index of the least-significant
// set bit in any of the ranges for this state, since this tells us how many
// bits we can discard and still determine what range a byte lies in. Sadly
// it appears that ffs() is not portable, so we do it clumsily.
uint8_t shift = 7;
for (State::const_iterator range_it = state_it->begin();
range_it != state_it->end();
++range_it) {
while (shift > 0 && range_it->from % (1 << shift) != 0) {
--shift;
}
}
shifts.push_back(shift);
pos += 1 + (1 << (7 - shift));
state_offset.push_back(pos);
}
DCHECK_EQ(129, state_offset[1]);
fputs(kProlog, stream);
TablePrinter table_printer(stream);
for (uint8_t state_index = 0; state_index < states.size(); ++state_index) {
const uint8_t shift = shifts[state_index];
uint8_t next_range = 0;
uint8_t target_state = 1;
fprintf(stream,
" // State %d, offset 0x%02x\n",
static_cast<int>(state_index),
static_cast<int>(state_offset[state_index]));
table_printer.PrintValue(shift);
for (int i = 0; i < 0x100; i += (1 << shift)) {
if (next_range < states[state_index].size() &&
states[state_index][next_range].from == i) {
target_state = states[state_index][next_range].target_state;
++next_range;
}
if (i >= 0x80) {
table_printer.PrintValue(state_offset[target_state]);
}
}
table_printer.NewLine();
}
fputs(kEpilog, stream);
}
} // namespace
int main(int argc, char* argv[]) {
base::CommandLine::Init(argc, argv);
logging::LoggingSettings settings;
settings.logging_dest = logging::LOG_TO_SYSTEM_DEBUG_LOG;
logging::InitLogging(settings);
if (base::CommandLine::ForCurrentProcess()->HasSwitch("help")) {
fwrite(kHelpText, 1, arraysize(kHelpText), stdout);
exit(EXIT_SUCCESS);
}
base::FilePath filename =
base::CommandLine::ForCurrentProcess()->GetSwitchValuePath("output");
FILE* output = stdout;
if (!filename.empty()) {
output = base::OpenFile(filename, "wb");
if (!output)
PLOG(FATAL) << "Couldn't open '" << filename.AsUTF8Unsafe()
<< "' for writing";
}
// Step 1: Enumerate the characters
PairVector pairs = InitializeCharacters();
// Step 2: Convert to sets.
MoveAllCharsToSets(&pairs);
if (VLOG_IS_ON(1)) {
LogStringSets(pairs);
}
// Step 3: Generate states.
std::vector<State> states = GenerateStates(pairs);
// Step 4/5: Print output
PrintStates(states, output);
if (!filename.empty()) {
if (!base::CloseFile(output))
PLOG(FATAL) << "Couldn't finish writing '" << filename.AsUTF8Unsafe()
<< "'";
}
return EXIT_SUCCESS;
}