ClickHouse/dbms/src/Functions/firstSignificantSubdomain.h

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#pragma once
#include <Functions/domain.h>
#include <common/find_symbols.h>
namespace DB
{
struct ExtractFirstSignificantSubdomain
{
static size_t getReserveLengthForElement() { return 10; }
static void execute(const Pos data, const size_t size, Pos & res_data, size_t & res_size, Pos * out_domain_end = nullptr)
{
res_data = data;
res_size = 0;
Pos tmp;
size_t domain_length;
ExtractDomain<true>::execute(data, size, tmp, domain_length);
if (domain_length == 0)
return;
if (out_domain_end)
*out_domain_end = tmp + domain_length;
/// cut useless dot
if (tmp[domain_length - 1] == '.')
--domain_length;
res_data = tmp;
res_size = domain_length;
auto begin = tmp;
auto end = begin + domain_length;
const char * last_3_periods[3]{};
auto pos = find_first_symbols<'.'>(begin, end);
while (pos < end)
{
last_3_periods[2] = last_3_periods[1];
last_3_periods[1] = last_3_periods[0];
last_3_periods[0] = pos;
pos = find_first_symbols<'.'>(pos + 1, end);
}
if (!last_3_periods[0])
return;
if (!last_3_periods[1])
{
res_size = last_3_periods[0] - begin;
return;
}
if (!last_3_periods[2])
last_3_periods[2] = begin - 1;
size_t size_of_second_subdomain_plus_period = last_3_periods[0] - last_3_periods[1];
if (size_of_second_subdomain_plus_period == 4 || size_of_second_subdomain_plus_period == 3)
{
/// We will key by four bytes that are either ".xyz" or ".xy.".
UInt32 key = unalignedLoad<UInt32>(last_3_periods[1]);
/// NOTE: assuming little endian.
/// NOTE: does the compiler generate SIMD code?
/// NOTE: for larger amount of cases we can use a perfect hash table (see 'gperf' as an example).
if ( key == '.' + 'c' * 0x100U + 'o' * 0x10000U + 'm' * 0x1000000U
|| key == '.' + 'n' * 0x100U + 'e' * 0x10000U + 't' * 0x1000000U
|| key == '.' + 'o' * 0x100U + 'r' * 0x10000U + 'g' * 0x1000000U
|| key == '.' + 'b' * 0x100U + 'i' * 0x10000U + 'z' * 0x1000000U
|| key == '.' + 'g' * 0x100U + 'o' * 0x10000U + 'v' * 0x1000000U
|| key == '.' + 'm' * 0x100U + 'i' * 0x10000U + 'l' * 0x1000000U
|| key == '.' + 'e' * 0x100U + 'd' * 0x10000U + 'u' * 0x1000000U
|| key == '.' + 'c' * 0x100U + 'o' * 0x10000U + '.' * 0x1000000U)
{
res_data += last_3_periods[2] + 1 - begin;
res_size = last_3_periods[1] - last_3_periods[2] - 1;
return;
}
}
res_data += last_3_periods[1] + 1 - begin;
res_size = last_3_periods[0] - last_3_periods[1] - 1;
}
};
}