ClickHouse/dbms/src/Functions/EmptyImpl.h

#pragma once
#include <cstring>
#include <Columns/ColumnString.h>
#include <Functions/FunctionFactory.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
}


template <bool negative = false>
struct EmptyImpl
{
    /// If the function will return constant value for FixedString data type.
    static constexpr auto is_fixed_to_constant = false;

    static void vector(const ColumnString::Chars & /*data*/, const ColumnString::Offsets & offsets, PaddedPODArray<UInt8> & res)
    {
        size_t size = offsets.size();
        ColumnString::Offset prev_offset = 1;
        for (size_t i = 0; i < size; ++i)
        {
            res[i] = negative ^ (offsets[i] == prev_offset);
            prev_offset = offsets[i] + 1;
        }
    }

    /// Only make sense if is_fixed_to_constant.
    static void vector_fixed_to_constant(const ColumnString::Chars & /*data*/, size_t /*n*/, UInt8 & /*res*/)
    {
        throw Exception("Logical error: 'vector_fixed_to_constant method' is called", ErrorCodes::LOGICAL_ERROR);
    }

    static void vector_fixed_to_vector(const ColumnString::Chars & data, size_t n, PaddedPODArray<UInt8> & res)
    {
        std::vector<char> empty_chars(n);
        size_t size = data.size() / n;

        for (size_t i = 0; i < size; ++i)
            res[i] = negative ^ (0 == memcmp(&data[i * n], empty_chars.data(), n));
    }

    static void array(const ColumnString::Offsets & offsets, PaddedPODArray<UInt8> & res)
    {
        size_t size = offsets.size();
        ColumnString::Offset prev_offset = 0;
        for (size_t i = 0; i < size; ++i)
        {
            res[i] = negative ^ (offsets[i] == prev_offset);
            prev_offset = offsets[i];
        }
    }
};

}