ClickHouse/dbms/src/Common/Volnitsky.h
2019-06-16 21:13:39 +03:00

660 lines
28 KiB
C++

#pragma once
#include <algorithm>
#include <vector>
#include <stdint.h>
#include <string.h>
#include <Core/Types.h>
#include <Poco/UTF8Encoding.h>
#include <Poco/Unicode.h>
#include <Common/StringSearcher.h>
#include <Common/StringUtils/StringUtils.h>
#include <common/StringRef.h>
#include <common/unaligned.h>
/** Search for a substring in a string by Volnitsky's algorithm
* http://volnitsky.com/project/str_search/
*
* `haystack` and `needle` can contain zero bytes.
*
* Algorithm:
* - if the `needle` is too small or too large, or too small `haystack`, use std::search or memchr;
* - when initializing, fill in an open-addressing linear probing hash table of the form
* hash from the bigram of needle -> the position of this bigram in needle + 1.
* (one is added only to distinguish zero offset from an empty cell)
* - the keys are not stored in the hash table, only the values are stored;
* - bigrams can be inserted several times if they occur in the needle several times;
* - when searching, take from haystack bigram, which should correspond to the last bigram of needle (comparing from the end);
* - look for it in the hash table, if found - get the offset from the hash table and compare the string bytewise;
* - if it did not match, we check the next cell of the hash table from the collision resolution chain;
* - if not found, skip to haystack almost the size of the needle bytes;
*
* MultiVolnitsky - search for multiple substrings in a string:
* - Add bigrams to hash table with string index. Then the usual Volnitsky search is used.
* - We are adding while searching, limiting the number of fallback searchers and the total number of added bigrams
*/
namespace DB
{
namespace VolnitskyTraits
{
using Offset = UInt8; /// Offset in the needle. For the basic algorithm, the length of the needle must not be greater than 255.
using Id = UInt8; /// Index of the string (within the array of multiple needles), must not be greater than 255.
using Ngram = UInt16; /// n-gram (2 bytes).
/** Fits into the L2 cache (of common Intel CPUs).
* This number is extremely good for compilers as it is numeric_limits<Uint16>::max() and there are optimizations with movzwl and other instructions with 2 bytes
*/
static constexpr size_t hash_size = 64 * 1024;
/// min haystack size to use main algorithm instead of fallback
static constexpr size_t min_haystack_size_for_algorithm = 20000;
static inline bool isFallbackNeedle(const size_t needle_size, size_t haystack_size_hint = 0)
{
return needle_size < 2 * sizeof(Ngram) || needle_size >= std::numeric_limits<Offset>::max()
|| (haystack_size_hint && haystack_size_hint < min_haystack_size_for_algorithm);
}
static inline Ngram toNGram(const UInt8 * const pos) { return unalignedLoad<Ngram>(pos); }
template <typename Callback>
static inline void putNGramASCIICaseInsensitive(const UInt8 * const pos, const int offset, const Callback & putNGramBase)
{
struct Chars
{
UInt8 c0;
UInt8 c1;
};
union
{
Ngram n;
Chars chars;
};
n = toNGram(pos);
const auto c0_al = isAlphaASCII(chars.c0);
const auto c1_al = isAlphaASCII(chars.c1);
if (c0_al && c1_al)
{
/// 4 combinations: AB, aB, Ab, ab
putNGramBase(n, offset);
chars.c0 = alternateCaseIfAlphaASCII(chars.c0);
putNGramBase(n, offset);
chars.c1 = alternateCaseIfAlphaASCII(chars.c1);
putNGramBase(n, offset);
chars.c0 = alternateCaseIfAlphaASCII(chars.c0);
putNGramBase(n, offset);
}
else if (c0_al)
{
/// 2 combinations: A1, a1
putNGramBase(n, offset);
chars.c0 = alternateCaseIfAlphaASCII(chars.c0);
putNGramBase(n, offset);
}
else if (c1_al)
{
/// 2 combinations: 0B, 0b
putNGramBase(n, offset);
chars.c1 = alternateCaseIfAlphaASCII(chars.c1);
putNGramBase(n, offset);
}
else
/// 1 combination: 01
putNGramBase(n, offset);
}
template <bool CaseSensitive, bool ASCII, typename Callback>
static inline void putNGram(const UInt8 * const pos, const int offset, [[maybe_unused]] const UInt8 * const begin, const Callback & putNGramBase)
{
if constexpr (CaseSensitive)
{
putNGramBase(toNGram(pos), offset);
}
else
{
if constexpr (ASCII)
{
putNGramASCIICaseInsensitive(pos, offset, putNGramBase);
}
else
{
struct Chars
{
UInt8 c0;
UInt8 c1;
};
union
{
VolnitskyTraits::Ngram n;
Chars chars;
};
n = toNGram(pos);
if (isascii(chars.c0) && isascii(chars.c1))
putNGramASCIICaseInsensitive(pos, offset, putNGramBase);
else
{
/** n-gram (in the case of n = 2)
* can be entirely located within one code point,
* or intersect with two code points.
*
* In the first case, you need to consider up to two alternatives - this code point in upper and lower case,
* and in the second case - up to four alternatives - fragments of two code points in all combinations of cases.
*
* It does not take into account the dependence of the case-transformation from the locale (for example - Turkish `Ii`)
* as well as composition / decomposition and other features.
*
* It also does not work if characters with lower and upper cases are represented by different number of bytes or code points.
*/
using Seq = UInt8[6];
static const Poco::UTF8Encoding utf8;
if (UTF8::isContinuationOctet(chars.c1))
{
/// ngram is inside a sequence
auto seq_pos = pos;
UTF8::syncBackward(seq_pos, begin);
const auto u32 = utf8.convert(seq_pos);
const auto l_u32 = Poco::Unicode::toLower(u32);
const auto u_u32 = Poco::Unicode::toUpper(u32);
/// symbol is case-independent
if (l_u32 == u_u32)
putNGramBase(n, offset);
else
{
/// where is the given ngram in respect to the start of UTF-8 sequence?
const auto seq_ngram_offset = pos - seq_pos;
Seq seq;
/// put ngram for lowercase
utf8.convert(l_u32, seq, sizeof(seq));
chars.c0 = seq[seq_ngram_offset];
chars.c1 = seq[seq_ngram_offset + 1];
putNGramBase(n, offset);
/// put ngram for uppercase
utf8.convert(u_u32, seq, sizeof(seq));
chars.c0 = seq[seq_ngram_offset]; //-V519
chars.c1 = seq[seq_ngram_offset + 1]; //-V519
putNGramBase(n, offset);
}
}
else
{
/// ngram is on the boundary of two sequences
/// first sequence may start before u_pos if it is not ASCII
auto first_seq_pos = pos;
UTF8::syncBackward(first_seq_pos, begin);
/// where is the given ngram in respect to the start of first UTF-8 sequence?
const auto seq_ngram_offset = pos - first_seq_pos;
const auto first_u32 = utf8.convert(first_seq_pos);
const auto first_l_u32 = Poco::Unicode::toLower(first_u32);
const auto first_u_u32 = Poco::Unicode::toUpper(first_u32);
/// second sequence always start immediately after u_pos
auto second_seq_pos = pos + 1;
const auto second_u32 = utf8.convert(second_seq_pos); /// TODO This assumes valid UTF-8 or zero byte after needle.
const auto second_l_u32 = Poco::Unicode::toLower(second_u32);
const auto second_u_u32 = Poco::Unicode::toUpper(second_u32);
/// both symbols are case-independent
if (first_l_u32 == first_u_u32 && second_l_u32 == second_u_u32)
{
putNGramBase(n, offset);
}
else if (first_l_u32 == first_u_u32)
{
/// first symbol is case-independent
Seq seq;
/// put ngram for lowercase
utf8.convert(second_l_u32, seq, sizeof(seq));
chars.c1 = seq[0];
putNGramBase(n, offset);
/// put ngram from uppercase, if it is different
utf8.convert(second_u_u32, seq, sizeof(seq));
if (chars.c1 != seq[0])
{
chars.c1 = seq[0];
putNGramBase(n, offset);
}
}
else if (second_l_u32 == second_u_u32)
{
/// second symbol is case-independent
Seq seq;
/// put ngram for lowercase
utf8.convert(first_l_u32, seq, sizeof(seq));
chars.c0 = seq[seq_ngram_offset];
putNGramBase(n, offset);
/// put ngram for uppercase, if it is different
utf8.convert(first_u_u32, seq, sizeof(seq));
if (chars.c0 != seq[seq_ngram_offset])
{
chars.c0 = seq[seq_ngram_offset];
putNGramBase(n, offset);
}
}
else
{
Seq first_l_seq;
Seq first_u_seq;
Seq second_l_seq;
Seq second_u_seq;
utf8.convert(first_l_u32, first_l_seq, sizeof(first_l_seq));
utf8.convert(first_u_u32, first_u_seq, sizeof(first_u_seq));
utf8.convert(second_l_u32, second_l_seq, sizeof(second_l_seq));
utf8.convert(second_u_u32, second_u_seq, sizeof(second_u_seq));
auto c0l = first_l_seq[seq_ngram_offset];
auto c0u = first_u_seq[seq_ngram_offset];
auto c1l = second_l_seq[0];
auto c1u = second_u_seq[0];
/// ngram for ll
chars.c0 = c0l;
chars.c1 = c1l;
putNGramBase(n, offset);
if (c0l != c0u)
{
/// ngram for Ul
chars.c0 = c0u;
chars.c1 = c1l;
putNGramBase(n, offset);
}
if (c1l != c1u)
{
/// ngram for lU
chars.c0 = c0l;
chars.c1 = c1u;
putNGramBase(n, offset);
}
if (c0l != c0u && c1l != c1u)
{
/// ngram for UU
chars.c0 = c0u;
chars.c1 = c1u;
putNGramBase(n, offset);
}
}
}
}
}
}
}
}
/// @todo store lowercase needle to speed up in case there are numerous occurrences of bigrams from needle in haystack
template <bool CaseSensitive, bool ASCII, typename FallbackSearcher>
class VolnitskyBase
{
protected:
const UInt8 * const needle;
const size_t needle_size;
const UInt8 * const needle_end = needle + needle_size;
/// For how long we move, if the n-gram from haystack is not found in the hash table.
const size_t step = needle_size - sizeof(VolnitskyTraits::Ngram) + 1;
/** max needle length is 255, max distinct ngrams for case-sensitive is (255 - 1), case-insensitive is 4 * (255 - 1)
* storage of 64K ngrams (n = 2, 128 KB) should be large enough for both cases */
VolnitskyTraits::Offset hash[VolnitskyTraits::hash_size]; /// Hash table.
const bool fallback; /// Do we need to use the fallback algorithm.
FallbackSearcher fallback_searcher;
public:
/** haystack_size_hint - the expected total size of the haystack for `search` calls. Optional (zero means unspecified).
* If you specify it small enough, the fallback algorithm will be used,
* since it is considered that it's useless to waste time initializing the hash table.
*/
VolnitskyBase(const char * const needle, const size_t needle_size, size_t haystack_size_hint = 0)
: needle{reinterpret_cast<const UInt8 *>(needle)}
, needle_size{needle_size}
, fallback{VolnitskyTraits::isFallbackNeedle(needle_size, haystack_size_hint)}
, fallback_searcher{needle, needle_size}
{
if (fallback)
return;
memset(hash, 0, sizeof(hash));
auto callback = [this](const VolnitskyTraits::Ngram ngram, const int offset) { return this->putNGramBase(ngram, offset); };
/// ssize_t is used here because unsigned can't be used with condition like `i >= 0`, unsigned always >= 0
/// And also adding from the end guarantees that we will find first occurence because we will lookup bigger offsets first.
for (auto i = static_cast<ssize_t>(needle_size - sizeof(VolnitskyTraits::Ngram)); i >= 0; --i)
VolnitskyTraits::putNGram<CaseSensitive, ASCII>(this->needle + i, i + 1, this->needle, callback);
}
/// If not found, the end of the haystack is returned.
const UInt8 * search(const UInt8 * const haystack, const size_t haystack_size) const
{
if (needle_size == 0)
return haystack;
const auto haystack_end = haystack + haystack_size;
if (fallback || haystack_size <= needle_size)
return fallback_searcher.search(haystack, haystack_end);
/// Let's "apply" the needle to the haystack and compare the n-gram from the end of the needle.
const auto * pos = haystack + needle_size - sizeof(VolnitskyTraits::Ngram);
for (; pos <= haystack_end - needle_size; pos += step)
{
/// We look at all the cells of the hash table that can correspond to the n-gram from haystack.
for (size_t cell_num = VolnitskyTraits::toNGram(pos) % VolnitskyTraits::hash_size; hash[cell_num];
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size)
{
/// When found - compare bytewise, using the offset from the hash table.
const auto res = pos - (hash[cell_num] - 1);
/// pointer in the code is always padded array so we can use pagesafe semantics
if (fallback_searcher.compare(res))
return res;
}
}
return fallback_searcher.search(pos - step + 1, haystack_end);
}
const char * search(const char * haystack, size_t haystack_size) const
{
return reinterpret_cast<const char *>(search(reinterpret_cast<const UInt8 *>(haystack), haystack_size));
}
protected:
void putNGramBase(const VolnitskyTraits::Ngram ngram, const int offset)
{
/// Put the offset for the n-gram in the corresponding cell or the nearest free cell.
size_t cell_num = ngram % VolnitskyTraits::hash_size;
while (hash[cell_num])
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size; /// Search for the next free cell.
hash[cell_num] = offset;
}
};
template <bool CaseSensitive, bool ASCII, typename FallbackSearcher>
class MultiVolnitskyBase
{
private:
/// needles and their offsets
const std::vector<StringRef> & needles;
/// fallback searchers
std::vector<size_t> fallback_needles;
std::vector<FallbackSearcher> fallback_searchers;
/// because std::pair<> is not POD
struct OffsetId
{
VolnitskyTraits::Id id;
VolnitskyTraits::Offset off;
};
OffsetId hash[VolnitskyTraits::hash_size];
/// step for each bunch of strings
size_t step;
/// last index of offsets that was not processed
size_t last;
/// limit for adding to hashtable. In worst case with case insentive search, the table will be filled at most as half
static constexpr size_t small_limit = VolnitskyTraits::hash_size / 8;
public:
MultiVolnitskyBase(const std::vector<StringRef> & needles_) : needles{needles_}, step{0}, last{0}
{
fallback_searchers.reserve(needles.size());
}
/**
* This function is needed to initialize hash table
* Returns `true` if there is nothing to initialize
* and `false` if we have something to initialize and initializes it.
* This function is a kind of fallback if there are many needles.
* We actually destroy the hash table and initialize it with uninitialized needles
* and search through the haystack again.
* The actual usage of this function is like this:
* while (hasMoreToSearch())
* {
* search inside the haystack with the known needles
* }
*/
bool hasMoreToSearch()
{
if (last == needles.size())
return false;
memset(hash, 0, sizeof(hash));
fallback_needles.clear();
step = std::numeric_limits<size_t>::max();
size_t buf = 0;
size_t size = needles.size();
for (; last < size; ++last)
{
const char * cur_needle_data = needles[last].data;
const size_t cur_needle_size = needles[last].size;
/// save the indices of fallback searchers
if (VolnitskyTraits::isFallbackNeedle(cur_needle_size))
{
fallback_needles.push_back(last);
}
else
{
/// put all bigrams
auto callback = [this](const VolnitskyTraits::Ngram ngram, const int offset)
{
return this->putNGramBase(ngram, offset, this->last);
};
buf += cur_needle_size - sizeof(VolnitskyTraits::Ngram) + 1;
/// this is the condition when we actually need to stop and start searching with known needles
if (buf > small_limit)
break;
step = std::min(step, cur_needle_size - sizeof(VolnitskyTraits::Ngram) + 1);
for (auto i = static_cast<int>(cur_needle_size - sizeof(VolnitskyTraits::Ngram)); i >= 0; --i)
{
VolnitskyTraits::putNGram<CaseSensitive, ASCII>(
reinterpret_cast<const UInt8 *>(cur_needle_data) + i,
i + 1,
reinterpret_cast<const UInt8 *>(cur_needle_data),
callback);
}
}
fallback_searchers.emplace_back(cur_needle_data, cur_needle_size);
}
return true;
}
inline bool searchOne(const UInt8 * haystack, const UInt8 * haystack_end) const
{
const size_t fallback_size = fallback_needles.size();
for (size_t i = 0; i < fallback_size; ++i)
if (fallback_searchers[fallback_needles[i]].search(haystack, haystack_end) != haystack_end)
return true;
/// check if we have one non empty volnitsky searcher
if (step != std::numeric_limits<size_t>::max())
{
const auto * pos = haystack + step - sizeof(VolnitskyTraits::Ngram);
for (; pos <= haystack_end - sizeof(VolnitskyTraits::Ngram); pos += step)
{
for (size_t cell_num = VolnitskyTraits::toNGram(pos) % VolnitskyTraits::hash_size; hash[cell_num].off;
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size)
{
if (pos >= haystack + hash[cell_num].off - 1)
{
const auto res = pos - (hash[cell_num].off - 1);
const size_t ind = hash[cell_num].id;
if (res + needles[ind].size <= haystack_end && fallback_searchers[ind].compare(res))
return true;
}
}
}
}
return false;
}
inline size_t searchOneFirstIndex(const UInt8 * haystack, const UInt8 * haystack_end) const
{
const size_t fallback_size = fallback_needles.size();
size_t ans = std::numeric_limits<size_t>::max();
for (size_t i = 0; i < fallback_size; ++i)
if (fallback_searchers[fallback_needles[i]].search(haystack, haystack_end) != haystack_end)
ans = std::min(ans, fallback_needles[i]);
/// check if we have one non empty volnitsky searcher
if (step != std::numeric_limits<size_t>::max())
{
const auto * pos = haystack + step - sizeof(VolnitskyTraits::Ngram);
for (; pos <= haystack_end - sizeof(VolnitskyTraits::Ngram); pos += step)
{
for (size_t cell_num = VolnitskyTraits::toNGram(pos) % VolnitskyTraits::hash_size; hash[cell_num].off;
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size)
{
if (pos >= haystack + hash[cell_num].off - 1)
{
const auto res = pos - (hash[cell_num].off - 1);
const size_t ind = hash[cell_num].id;
if (res + needles[ind].size <= haystack_end && fallback_searchers[ind].compare(res))
ans = std::min(ans, ind);
}
}
}
}
/*
* if nothing was found, ans + 1 will be equal to zero and we can
* assign it into the result because we need to return the position starting with one
*/
return ans + 1;
}
template <typename CountCharsCallback>
inline UInt64 searchOneFirstPosition(const UInt8 * haystack, const UInt8 * haystack_end, const CountCharsCallback & count_chars) const
{
const size_t fallback_size = fallback_needles.size();
UInt64 ans = std::numeric_limits<UInt64>::max();
for (size_t i = 0; i < fallback_size; ++i)
if (auto pos = fallback_searchers[fallback_needles[i]].search(haystack, haystack_end); pos != haystack_end)
ans = std::min<UInt64>(ans, pos - haystack);
/// check if we have one non empty volnitsky searcher
if (step != std::numeric_limits<size_t>::max())
{
const auto * pos = haystack + step - sizeof(VolnitskyTraits::Ngram);
for (; pos <= haystack_end - sizeof(VolnitskyTraits::Ngram); pos += step)
{
for (size_t cell_num = VolnitskyTraits::toNGram(pos) % VolnitskyTraits::hash_size; hash[cell_num].off;
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size)
{
if (pos >= haystack + hash[cell_num].off - 1)
{
const auto res = pos - (hash[cell_num].off - 1);
const size_t ind = hash[cell_num].id;
if (res + needles[ind].size <= haystack_end && fallback_searchers[ind].compare(res))
ans = std::min<UInt64>(ans, res - haystack);
}
}
}
}
if (ans == std::numeric_limits<UInt64>::max())
return 0;
return count_chars(haystack, haystack + ans);
}
template <typename CountCharsCallback, typename AnsType>
inline void searchOneAll(const UInt8 * haystack, const UInt8 * haystack_end, AnsType * ans, const CountCharsCallback & count_chars) const
{
const size_t fallback_size = fallback_needles.size();
for (size_t i = 0; i < fallback_size; ++i)
{
const UInt8 * ptr = fallback_searchers[fallback_needles[i]].search(haystack, haystack_end);
if (ptr != haystack_end)
ans[fallback_needles[i]] = count_chars(haystack, ptr);
}
/// check if we have one non empty volnitsky searcher
if (step != std::numeric_limits<size_t>::max())
{
const auto * pos = haystack + step - sizeof(VolnitskyTraits::Ngram);
for (; pos <= haystack_end - sizeof(VolnitskyTraits::Ngram); pos += step)
{
for (size_t cell_num = VolnitskyTraits::toNGram(pos) % VolnitskyTraits::hash_size; hash[cell_num].off;
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size)
{
if (pos >= haystack + hash[cell_num].off - 1)
{
const auto * res = pos - (hash[cell_num].off - 1);
const size_t ind = hash[cell_num].id;
if (ans[ind] == 0 && res + needles[ind].size <= haystack_end && fallback_searchers[ind].compare(res))
ans[ind] = count_chars(haystack, res);
}
}
}
}
}
void putNGramBase(const VolnitskyTraits::Ngram ngram, const int offset, const size_t num)
{
size_t cell_num = ngram % VolnitskyTraits::hash_size;
while (hash[cell_num].off)
cell_num = (cell_num + 1) % VolnitskyTraits::hash_size;
hash[cell_num] = {static_cast<VolnitskyTraits::Id>(num), static_cast<VolnitskyTraits::Offset>(offset)};
}
};
using Volnitsky = VolnitskyBase<true, true, ASCIICaseSensitiveStringSearcher>;
using VolnitskyUTF8 = VolnitskyBase<true, false, ASCIICaseSensitiveStringSearcher>; /// exactly same as Volnitsky
using VolnitskyCaseInsensitive = VolnitskyBase<false, true, ASCIICaseInsensitiveStringSearcher>; /// ignores non-ASCII bytes
using VolnitskyCaseInsensitiveUTF8 = VolnitskyBase<false, false, UTF8CaseInsensitiveStringSearcher>;
using MultiVolnitsky = MultiVolnitskyBase<true, true, ASCIICaseSensitiveStringSearcher>;
using MultiVolnitskyUTF8 = MultiVolnitskyBase<true, false, ASCIICaseSensitiveStringSearcher>;
using MultiVolnitskyCaseInsensitive = MultiVolnitskyBase<false, true, ASCIICaseInsensitiveStringSearcher>;
using MultiVolnitskyCaseInsensitiveUTF8 = MultiVolnitskyBase<false, false, UTF8CaseInsensitiveStringSearcher>;
}