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

#pragma once

#include <string.h>

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


class Collator;


namespace DB
{

/** Column for String values.
  */
class ColumnString final : public IColumn
{
public:
	using Chars_t = PaddedPODArray<UInt8>;

private:
	/// Maps i'th position to offset to i+1'th element. Last offset maps to the end of all chars (is the size of all chars).
	Offsets_t offsets;

	/// Bytes of strings, placed contiguously.
	/// For convenience, every string ends with terminating zero byte. Note that strings could contain zero bytes in the middle.
	Chars_t chars;

	size_t __attribute__((__always_inline__)) offsetAt(size_t i) const	{ return i == 0 ? 0 : offsets[i - 1]; }

	/// Size of i-th element, including terminating zero.
	size_t __attribute__((__always_inline__)) sizeAt(size_t i) const	{ return i == 0 ? offsets[0] : (offsets[i] - offsets[i - 1]); }

	template <bool positive>
	struct less;

	template <bool positive>
	struct lessWithCollation;

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

	size_t size() const override
	{
		return offsets.size();
	}

	size_t byteSize() const override
	{
		return chars.size() + offsets.size() * sizeof(offsets[0]);
	}

	size_t allocatedSize() const override
	{
		return chars.allocated_size() + offsets.allocated_size() * sizeof(offsets[0]);
	}

	ColumnPtr cloneResized(size_t to_size) const override;

	Field operator[](size_t n) const override
	{
		return Field(&chars[offsetAt(n)], sizeAt(n) - 1);
	}

	void get(size_t n, Field & res) const override
	{
		res.assignString(&chars[offsetAt(n)], sizeAt(n) - 1);
	}

	StringRef getDataAt(size_t n) const override
	{
		return StringRef(&chars[offsetAt(n)], sizeAt(n) - 1);
	}

	StringRef getDataAtWithTerminatingZero(size_t n) const override
	{
		return StringRef(&chars[offsetAt(n)], sizeAt(n));
	}

	void insert(const Field & x) override
	{
		const String & s = DB::get<const String &>(x);
		const size_t old_size = chars.size();
		const size_t size_to_append = s.size() + 1;
		const size_t new_size = old_size + size_to_append;

		chars.resize(new_size);
		memcpy(&chars[old_size], s.c_str(), size_to_append);
		offsets.push_back(new_size);
	}

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

		if (n != 0)
		{
			const size_t size_to_append = src.offsets[n] - src.offsets[n - 1];

			if (size_to_append == 1)
			{
				/// shortcut for empty string
				chars.push_back(0);
				offsets.push_back(chars.size());
			}
			else
			{
				const size_t old_size = chars.size();
				const size_t offset = src.offsets[n - 1];
				const size_t new_size = old_size + size_to_append;

				chars.resize(new_size);
				memcpySmallAllowReadWriteOverflow15(&chars[old_size], &src.chars[offset], size_to_append);
				offsets.push_back(new_size);
			}
		}
		else
		{
			const size_t old_size = chars.size();
			const size_t size_to_append = src.offsets[0];
			const size_t new_size = old_size + size_to_append;

			chars.resize(new_size);
			memcpySmallAllowReadWriteOverflow15(&chars[old_size], &src.chars[0], size_to_append);
			offsets.push_back(new_size);
		}
	}

	void insertData(const char * pos, size_t length) override
	{
		const size_t old_size = chars.size();
		const size_t new_size = old_size + length + 1;

		chars.resize(new_size);
		memcpy(&chars[old_size], pos, length);
		chars[old_size + length] = 0;
		offsets.push_back(new_size);
	}

	void insertDataWithTerminatingZero(const char * pos, size_t length) override
	{
		const size_t old_size = chars.size();
		const size_t new_size = old_size + length;

		chars.resize(new_size);
		memcpy(&chars[old_size], pos, length);
		offsets.push_back(new_size);
	}

	void popBack(size_t n) override
	{
		size_t nested_n = offsets.back() - offsetAt(offsets.size() - n);
		chars.resize(chars.size() - nested_n);
		offsets.resize_assume_reserved(offsets.size() - n);
	}

	StringRef serializeValueIntoArena(size_t n, Arena & arena, char const *& begin) const override
	{
		size_t string_size = sizeAt(n);
		size_t offset = offsetAt(n);

		StringRef res;
		res.size = sizeof(string_size) + string_size;
		char * pos = arena.allocContinue(res.size, begin);
		memcpy(pos, &string_size, sizeof(string_size));
		memcpy(pos + sizeof(string_size), &chars[offset], string_size);
		res.data = pos;

		return res;
	}

	const char * deserializeAndInsertFromArena(const char * pos) override
	{
		const size_t string_size = *reinterpret_cast<const size_t *>(pos);
		pos += sizeof(string_size);

		const size_t old_size = chars.size();
		const size_t new_size = old_size + string_size;
		chars.resize(new_size);
		memcpy(&chars[old_size], pos, string_size);

		offsets.push_back(new_size);
		return pos + string_size;
	}

	void updateHashWithValue(size_t n, SipHash & hash) const override
	{
		size_t string_size = sizeAt(n);
		size_t offset = offsetAt(n);

		hash.update(reinterpret_cast<const char *>(&string_size), sizeof(string_size));
		hash.update(reinterpret_cast<const char *>(&chars[offset]), string_size);
	}

	void insertRangeFrom(const IColumn & src, size_t start, size_t length) override;

	ColumnPtr filter(const Filter & filt, ssize_t result_size_hint) const override;

	ColumnPtr permute(const Permutation & perm, size_t limit) const override;

	void insertDefault() override
	{
		chars.push_back(0);
		offsets.push_back(offsets.size() == 0 ? 1 : (offsets.back() + 1));
	}

	int compareAt(size_t n, size_t m, const IColumn & rhs_, int nan_direction_hint) const override
	{
		const ColumnString & rhs = static_cast<const ColumnString &>(rhs_);

		/** For performance, the strings are compared to the first zero byte.
		  * (if zero byte is in the middle of the line, then what is after it is ignored)
		  * Note that the terminating zero byte is always present.
		  */
		return strcmp(
			reinterpret_cast<const char *>(&chars[offsetAt(n)]),
			reinterpret_cast<const char *>(&rhs.chars[rhs.offsetAt(m)]));
	}

	/// Variant of compareAt for string comparison with respect of collation.
	int compareAtWithCollation(size_t n, size_t m, const IColumn & rhs_, const Collator & collator) const;

	void getPermutation(bool reverse, size_t limit, Permutation & res) const override;

	/// Sorting with respect of collation.
	void getPermutationWithCollation(const Collator & collator, bool reverse, size_t limit, Permutation & res) const;

	ColumnPtr replicate(const Offsets_t & replicate_offsets) const override;

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

	void reserve(size_t n) override;

	void getExtremes(Field & min, Field & max) const override;

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

	Offsets_t & getOffsets() { return offsets; }
	const Offsets_t & getOffsets() const { return offsets; }
};


}