gplib/include/gp/quotient_filter.hpp

#pragma once

#include <gp/algorithm/foreach.hpp>
#include <gp/algorithm/tmp_manip.hpp>
#include <gp/array.hpp>
#include <gp/exception.hpp>

#include <atomic>

#include <stdint.h>

namespace gp {

	// TODO: Specify the concept of a skipstone

	/**
	 * @brief An abstraction for exploring and picking in a list sequencially
	 */
	struct linear_skipstone {
		constexpr static size_t ccbits = 1;
		constexpr static size_t cclast = 1;
		size_t ret = 0;
		void next() {
			++ret;
		}
		operator size_t() {
			return ret;
		}
	};

	/**
	 * @brief An abstraction for exploring and picking in a list in a non sequencial but still relatively cache friendly way
	 */
	struct stepcache_skipstone {
		constexpr static size_t ccbits = 7;
		constexpr static size_t cclast = 127;

		constexpr static size_t list[128] = {
			0,    1,    2,    3,
			8,    9,   10,   11,
			20,   21,   22,   23,
			36,   37,   38,   39,
			56,   57,   58,   59,
			80,   81,   82,   83,
			108,  109,  110,  111,
			140,  141,  142,  143,
			176,  177,  178,  179,
			216,  217,  218,  219,
			260,  261,  262,  263,
			308,  309,  310,  311,
			360,  361,  362,  363,
			416,  417,  418,  419,
			476,  477,  478,  479,
			540,  541,  542,  543,
			608,  609,  610,  611,
			680,  681,  682,  683,
			756,  757,  758,  759,
			836,  837,  838,  839,
			920,  921,  922,  923,
			1008, 1009, 1010, 1011,
			1100, 1101, 1102, 1103,
			1196, 1197, 1198, 1199,
			1296, 1297, 1298, 1299,
			1400, 1401, 1402, 1403,
			1508, 1509, 1510, 1511,
			1736, 1737, 1738, 1739,
			1856, 1857, 1858, 1859,
			1980, 1981, 1982, 1983,
			2108, 2109, 2110, 2111,
			2240, 2241, 2242, 2243
		};
		size_t ret = 0;
		void next() {
			++ret;
		}
		operator size_t() {
			[[unlikely]] if ( ret >= 128 )
				return ret+list[127];
			return list[ret];
		}
	};

	/**
	 * @brief A datastructure to accurately check belonging in a set in a probabilistic way.
	 * More precise than a bloomfilter, less space efficient, can allow deletion (handle with care)
	 * 
	 * @tparam hash_type the type of hash storage type
	 * @tparam magnitude the size of the filter as a power of 2
	 * @tparam remainder the number of bits of remainder of the quotient \f$\frac{h}{m}\f$ where \f$h\f$ is a hash and \f$m\f$ the magnitude of the set, can throw away bits
	 * @tparam skipstone_t the type of sequence exploration to perform
	 */
	template<typename hash_type = uint32_t, uint8_t magnitude = 20, uint8_t remainder = (8*sizeof(hash_type))-magnitude, typename skipstone_t = linear_skipstone>
	class quotient_filter {
		constexpr static size_t phys_size = (1 << magnitude) / 32;
		using rem_t = typename gp::either<(remainder<=16), uint16_t, uint32_t>::type;
		struct node{
			//rem_t ccount : skipstone_t::ccbits;
			rem_t is_occupied : 1;
			rem_t is_deleted : 1;
			rem_t r : remainder;
		};

		gp::array<
			node,
			1 << magnitude
		> data;

		void skipstone_killswitch(size_t q, size_t skip)
		{
			if(q == (q+skip)%data.size())
			{
				if constexpr (gp_config::has_exceptions)
				{
					throw gp::runtime_error("infinite skiploop detected");
				}
				else
				{
					exit((int)gp_errorcodes::infinite_skipstone);
				}
			}
		}

	public:
		quotient_filter() {
			gp::fill(data, node{0,0,0});
		}

		void set_hash(hash_type v)
		{
			const size_t q  = v & ((1 << magnitude)-1);
			const size_t r  = (v >> magnitude) & ((1 << remainder)-1);
			skipstone_t skip;

			for(;;)
			{
				auto& slot = data[(q+skip)%data.size()];
				if(slot.is_occupied)
				{
					if(slot.is_deleted)
					{
						slot.r = r;
						slot.is_deleted = false;
						for(;;)
						{
							skip.next();
							slot = data[(q+skip)%data.size()];
							if(!slot.is_occupied)
							{
								return;
							}
							else if(slot.r == r)
							{
								slot.is_deleted = true;
							}
							skipstone_killswitch(q, skip);
						}
					}
					if(slot.r == r)
					{
						return;
					}
					skip.next();
				}
				else
				{
					slot.r = r;
					slot.is_occupied = true;
					slot.is_deleted = false;
					return;
				}
				skipstone_killswitch(q, skip);
			}
		}

		bool test_hash(hash_type v)
		{
			const size_t q  = v & ((1 << magnitude)-1);
			const size_t r  = (v >> magnitude) & ((1 << remainder)-1);
			skipstone_t skip;

			for(;;)
			{
				auto& slot = data[(q+skip)%data.size()];
				if(slot.is_occupied)
				{
					if(!slot.is_deleted)
					{
						if(slot.r == r)
						{
							return true;
						}
					}
					skip.next();
				}
				else
				{
					return false;
				}
				skipstone_killswitch(q, skip);
			}
		}

		void remove_hash(hash_type v)
		{
			const size_t q  = v & ((1 << magnitude)-1);
			const size_t r  = (v >> magnitude) & ((1 << remainder)-1);
			skipstone_t skip;

			for(;;)
			{
				auto& slot = data[(q+skip)%data.size()];
				if(slot.is_occupied)
				{
					if(!slot.is_deleted)
					{
						if(slot.r == r)
						{
							slot.is_deleted = true;
							slot.is_occupied = false;
						}
					}
					skip.next();
				}
				else
				{
					return;
				}
				skipstone_killswitch(q, skip);
			}
		}
	};
}