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/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* String abstraction that avoids copies.
*/
#pragma once
#include <boost/noncopyable.hpp>
#include <unordered_map>
#include <memory>
#include <vector>
#include <string>
namespace yul
{
/// Repository for YulStrings.
/// Owns the string data for all YulStrings, which can be referenced by a Handle.
/// A Handle consists of an ID (that depends on the insertion order of YulStrings and is potentially
/// non-deterministic) and a deterministic string hash.
class YulStringRepository: boost::noncopyable
{
public:
struct Handle
{
size_t id;
std::uint64_t hash;
};
YulStringRepository():
m_strings{std::make_shared<std::string>()},
m_hashToID{std::make_pair(emptyHash(), 0)}
{}
static YulStringRepository& instance()
{
static YulStringRepository inst;
return inst;
}
Handle stringToHandle(std::string const& _string)
{
if (_string.empty())
return { 0, emptyHash() };
std::uint64_t h = hash(_string);
auto range = m_hashToID.equal_range(h);
for (auto it = range.first; it != range.second; ++it)
if (*m_strings[it->second] == _string)
return Handle{it->second, h};
m_strings.emplace_back(std::make_shared<std::string>(_string));
size_t id = m_strings.size() - 1;
m_hashToID.emplace_hint(range.second, std::make_pair(h, id));
return Handle{id, h};
}
std::string const& idToString(size_t _id) const { return *m_strings.at(_id); }
static std::uint64_t hash(std::string const& v)
{
// FNV hash - can be replaced by a better one, e.g. xxhash64
std::uint64_t hash = emptyHash();
for (auto c: v)
{
hash *= 1099511628211u;
hash ^= c;
}
return hash;
}
static constexpr std::uint64_t emptyHash() { return 14695981039346656037u; }
private:
std::vector<std::shared_ptr<std::string>> m_strings;
std::unordered_multimap<std::uint64_t, size_t> m_hashToID;
};
/// Wrapper around handles into the YulString repository.
/// Equality of two YulStrings is determined by comparing their ID.
/// The <-operator depends on the string hash and is not consistent
/// with string comparisons (however, it is still deterministic).
class YulString
{
public:
YulString() = default;
explicit YulString(std::string const& _s): m_handle(YulStringRepository::instance().stringToHandle(_s)) {}
YulString(YulString const&) = default;
YulString(YulString&&) = default;
YulString& operator=(YulString const&) = default;
YulString& operator=(YulString&&) = default;
/// This is not consistent with the string <-operator!
/// First compares the string hashes. If they are equal
/// it checks for identical IDs (only identical strings have
/// identical IDs and identical strings do not compare as "less").
/// If the hashes are identical and the strings are distinct, it
/// falls back to string comparison.
bool operator<(YulString const& _other) const
{
if (m_handle.hash < _other.m_handle.hash) return true;
if (_other.m_handle.hash < m_handle.hash) return false;
if (m_handle.id == _other.m_handle.id) return false;
return str() < _other.str();
}
/// Equality is determined based on the string ID.
bool operator==(YulString const& _other) const { return m_handle.id == _other.m_handle.id; }
bool operator!=(YulString const& _other) const { return m_handle.id != _other.m_handle.id; }
bool empty() const { return m_handle.id == 0; }
std::string const& str() const
{
return YulStringRepository::instance().idToString(m_handle.id);
}
private:
/// Handle of the string. Assumes that the empty string has ID zero.
YulStringRepository::Handle m_handle{ 0, YulStringRepository::emptyHash() };
};
}
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