ClickHouse/dbms/include/DB/Columns/ColumnFixedString.h

#pragma once

#include <string.h> // memcpy

#include <DB/Common/PODArray.h>
#include <DB/Common/Arena.h>
#include <DB/Common/SipHash.h>
#include <DB/Common/memcpySmall.h>
#include <DB/Columns/IColumn.h>
#include <DB/IO/ReadHelpers.h>
#include <DB/IO/WriteHelpers.h>


namespace DB
{

namespace ErrorCodes
{
	extern const int TOO_LARGE_STRING_SIZE;
	extern const int SIZE_OF_FIXED_STRING_DOESNT_MATCH;
	extern const int SIZES_OF_COLUMNS_DOESNT_MATCH;
	extern const int PARAMETER_OUT_OF_BOUND;
}

/** A column of values of "fixed-length string" type.
  * If you insert a smaller string, it will be padded with zero bytes.
  */
class ColumnFixedString final : public IColumn
{
public:
	using Chars_t = PaddedPODArray<UInt8>;

private:
	/// Bytes of rows, laid in succession. The strings are stored without a trailing zero byte.
	/** NOTE It is required that the offset and type of chars in the object be the same as that of `data in ColumnUInt8`.
	  * Used in `packFixed` function (AggregationCommon.h)
	  */
	Chars_t chars;
	/// The size of the rows.
	const size_t n;

public:
	/** Create an empty column of strings of fixed-length `n` */
	ColumnFixedString(size_t n_) : n(n_) {}

	std::string getName() const override { return "ColumnFixedString"; }

	ColumnPtr cloneResized(size_t size) const override
	{
		ColumnPtr new_col_holder = std::make_shared<ColumnFixedString>(n);

		if (size > 0)
		{
			auto & new_col = static_cast<ColumnFixedString &>(*new_col_holder);
			new_col.chars.resize(size * n);

			size_t count = std::min(this->size(), size);
			memcpy(&(new_col.chars[0]), &chars[0], count * n * sizeof(chars[0]));

			if (size > count)
				memset(&(new_col.chars[count * n]), '\0', (size - count) * n);
		}

		return new_col_holder;
	}

	size_t size() const override
	{
		return chars.size() / n;
	}

	size_t sizeOfField() const override
	{
		return n;
	}

	bool isFixed() const override
	{
		return true;
	}

	size_t byteSize() const override
	{
		return chars.size() + sizeof(n);
	}

	size_t allocatedSize() const override
	{
		return chars.allocated_size() + sizeof(n);
	}

	Field operator[](size_t index) const override
	{
		return String(reinterpret_cast<const char *>(&chars[n * index]), n);
	}

	void get(size_t index, Field & res) const override
	{
		res.assignString(reinterpret_cast<const char *>(&chars[n * index]), n);
	}

	StringRef getDataAt(size_t index) const override
	{
		return StringRef(&chars[n * index], n);
	}

	void insert(const Field & x) override
	{
		const String & s = DB::get<const String &>(x);

		if (s.size() > n)
			throw Exception("Too large string '" + s + "' for FixedString column", ErrorCodes::TOO_LARGE_STRING_SIZE);

		size_t old_size = chars.size();
		chars.resize_fill(old_size + n);
		memcpy(&chars[old_size], s.data(), s.size());
	}

	void insertFrom(const IColumn & src_, size_t index) override
	{
		const ColumnFixedString & src = static_cast<const ColumnFixedString &>(src_);

		if (n != src.getN())
			throw Exception("Size of FixedString doesn't match", ErrorCodes::SIZE_OF_FIXED_STRING_DOESNT_MATCH);

		size_t old_size = chars.size();
		chars.resize(old_size + n);
		memcpySmallAllowReadWriteOverflow15(&chars[old_size], &src.chars[n * index], n);
	}

	void insertData(const char * pos, size_t length) override
	{
		if (length > n)
			throw Exception("Too large string for FixedString column", ErrorCodes::TOO_LARGE_STRING_SIZE);

		size_t old_size = chars.size();
		chars.resize_fill(old_size + n);
		memcpy(&chars[old_size], pos, length);
	}

	void insertDefault() override
	{
		chars.resize_fill(chars.size() + n);
	}

	void popBack(size_t elems) override
	{
		chars.resize_assume_reserved(chars.size() - n * elems);
	}

	StringRef serializeValueIntoArena(size_t index, Arena & arena, char const *& begin) const override
	{
		auto pos = arena.allocContinue(n, begin);
		memcpy(pos, &chars[n * index], n);
		return StringRef(pos, n);
	}

	const char * deserializeAndInsertFromArena(const char * pos) override
	{
		size_t old_size = chars.size();
		chars.resize(old_size + n);
		memcpy(&chars[old_size], pos, n);
		return pos + n;
	}

	void updateHashWithValue(size_t index, SipHash & hash) const override
	{
		hash.update(reinterpret_cast<const char *>(&chars[n * index]), n);
	}

	int compareAt(size_t p1, size_t p2, const IColumn & rhs_, int nan_direction_hint) const override
	{
		const ColumnFixedString & rhs = static_cast<const ColumnFixedString &>(rhs_);
		return memcmp(&chars[p1 * n], &rhs.chars[p2 * n], n);
	}

	template <bool positive>
	struct less
	{
		const ColumnFixedString & parent;
		less(const ColumnFixedString & parent_) : parent(parent_) {}
		bool operator()(size_t lhs, size_t rhs) const
		{
			/// TODO: memcmp slows down.
			int res = memcmp(&parent.chars[lhs * parent.n], &parent.chars[rhs * parent.n], parent.n);
			return positive ? (res < 0) : (res > 0);
		}
	};

	void getPermutation(bool reverse, size_t limit, Permutation & res) const override
	{
		size_t s = size();
		res.resize(s);
		for (size_t i = 0; i < s; ++i)
			res[i] = i;

		if (limit >= s)
			limit = 0;

		if (limit)
		{
			if (reverse)
				std::partial_sort(res.begin(), res.begin() + limit, res.end(), less<false>(*this));
			else
				std::partial_sort(res.begin(), res.begin() + limit, res.end(), less<true>(*this));
		}
		else
		{
			if (reverse)
				std::sort(res.begin(), res.end(), less<false>(*this));
			else
				std::sort(res.begin(), res.end(), less<true>(*this));
		}
	}

	void insertRangeFrom(const IColumn & src, size_t start, size_t length) override
	{
		const ColumnFixedString & src_concrete = static_cast<const ColumnFixedString &>(src);

		if (start + length > src_concrete.size())
			throw Exception("Parameters start = "
				+ toString(start) + ", length = "
				+ toString(length) + " are out of bound in ColumnFixedString::insertRangeFrom method"
				" (size() = " + toString(src_concrete.size()) + ").",
				ErrorCodes::PARAMETER_OUT_OF_BOUND);

		size_t old_size = chars.size();
		chars.resize(old_size + length * n);
		memcpy(&chars[old_size], &src_concrete.chars[start * n], length * n);
	}

	ColumnPtr filter(const IColumn::Filter & filt, ssize_t result_size_hint) const override
	{
		size_t col_size = size();
		if (col_size != filt.size())
			throw Exception("Size of filter doesn't match size of column.", ErrorCodes::SIZES_OF_COLUMNS_DOESNT_MATCH);

		std::shared_ptr<ColumnFixedString> res = std::make_shared<ColumnFixedString>(n);

		if (result_size_hint)
			res->chars.reserve(result_size_hint > 0 ? result_size_hint * n : chars.size());

		size_t offset = 0;
		for (size_t i = 0; i < col_size; ++i, offset += n)
		{
			if (filt[i])
			{
				res->chars.resize(res->chars.size() + n);
				memcpySmallAllowReadWriteOverflow15(&res->chars[res->chars.size() - n], &chars[offset], n);
			}
		}

		return res;
	}

	ColumnPtr permute(const Permutation & perm, size_t limit) const override
	{
		size_t col_size = size();

		if (limit == 0)
			limit = col_size;
		else
			limit = std::min(col_size, limit);

		if (perm.size() < limit)
			throw Exception("Size of permutation is less than required.", ErrorCodes::SIZES_OF_COLUMNS_DOESNT_MATCH);

		if (limit == 0)
			return std::make_shared<ColumnFixedString>(n);

		std::shared_ptr<ColumnFixedString> res = std::make_shared<ColumnFixedString>(n);

		Chars_t & res_chars = res->chars;

		res_chars.resize(n * limit);

		size_t offset = 0;
		for (size_t i = 0; i < limit; ++i, offset += n)
			memcpySmallAllowReadWriteOverflow15(&res_chars[offset], &chars[perm[i] * n], n);

		return res;
	}

	ColumnPtr replicate(const Offsets_t & offsets) const override
	{
		size_t col_size = size();
		if (col_size != offsets.size())
			throw Exception("Size of offsets doesn't match size of column.", ErrorCodes::SIZES_OF_COLUMNS_DOESNT_MATCH);

		std::shared_ptr<ColumnFixedString> res = std::make_shared<ColumnFixedString>(n);

		if (0 == col_size)
			return res;

		Chars_t & res_chars = res->chars;
		res_chars.reserve(n * offsets.back());

		Offset_t prev_offset = 0;
		for (size_t i = 0; i < col_size; ++i)
		{
			size_t size_to_replicate = offsets[i] - prev_offset;
			prev_offset = offsets[i];

			for (size_t j = 0; j < size_to_replicate; ++j)
				for (size_t k = 0; k < n; ++k)
					res_chars.push_back(chars[i * n + k]);
		}

		return res;
	}

	Columns scatter(ColumnIndex num_columns, const Selector & selector) const override
	{
		return scatterImpl<ColumnFixedString>(num_columns, selector);
	}

	void reserve(size_t size) override
	{
		chars.reserve(n * size);
	};


	Chars_t & getChars() { return chars; }
	const Chars_t & getChars() const { return chars; }

	size_t getN() const { return n; }

	void getExtremes(Field & min, Field & max) const override
	{
		min = String();
		max = String();
	}
};


}