simap/vmap.h

#ifndef VMAP_H
#define VMAP_H
/*
 * A virtual memory misusing flat-ish hashmap optimized with AVX2.
 *
 * Structure
 *
 * VMEM
 * STRUCT
 * PRIVATE
 * UINTAPI
 */
#include <stdint.h>
#include "simd_map_lane.h"

/* VMEM */

#ifdef _WIN32
TODO: Utilize __Thread + SEH to implement lazy windows pageload zeroing
#else
/** Capacity should be multiple of 4096 for full pages */
static void *vm_reserve(ptrdiff_t capacity) {
	void *r = mmap(0, capacity, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
	return r==MAP_FAILED ? 0 : r;
}

/** Capacity should be multiple of 4096 for full pages and related to the ptr to free */
static char vm_free(void *ptr, ptrdiff_t capacity) {
	return !munmap(ptr, capacity);
}
#endif /* _WIN32 */

/* STRUCT */

struct vmap {
	/* using  uint8_t* here would simplify
	 * code except for aliasing rules */
	uint32_t *data;
	uint32_t count;
	uint32_t max_levels;
};
typedef struct vmap vmap;

/** The result of the search_all(..) operation */
struct vmap_find_res {
	/** The found location - or NULL when the key was not found */
	uint32_t *value_location;
	/** What 'level' depth this value was found. For multimap, but useful statistics */
	uint32_t level;
	/** Meta-data for continuation of the search. Tells which lane to search next A, B, C, or D */
	uint32_t lane_abcd_next;
	/** Meta-data for continuation of the search. In-lane where we search from next time? */
	int lane_next_begin;
};
typedef struct simd_map_find_res simd_map_find_res;

/* PRIVATE */

/* UINTAPI */

static inline vmap create_vmap(uint32_t max_levels) {
	vmap map{ NULL, 0, max_levels};
	map.data = (uint32_t *)vm_reserve(max_levels * 16 * 4096);
	return map;
}

static inline char free_vmap(vmap *map) {
	map->count = 0;
	return vm_free(map->data, map->max_levels * 16 * 4096);
}

/** Create the value for starting a search_all call */
static inline vmap_find_res vmap_search_all_begin() {
	vmap_find_res ret;
	ret.value_location = NULL;
	ret.level = 0;
	ret.lane_abcd_next = 0;
	ret.lane_next_begin = 0;
	return ret;
}

/**
 * Search the map in as a multimap - that is you can search multiple equal keyed values.
 * This is implemented by the result being understood also as a continuation alongside
 * a way to grab the pointer to the stored value and key (simd_map_lane_key_location(val)).
 *
 * @param map The map to search in
 * @param key The key to search for
 * @param prev The previous result if you continue your search. See: vmap_search_all_begin()
 * @returns Metadata + nullable ptr. See: vmap_find_res struct comments; ret.value_location
 */
static inline vmap_find_res search_all_vmap(vmap *map, uint32_t key, vmap_find_res prev) {
	/* Inits as not found, can change values */
	vmap_find_res ret = prev;

	uint32_t level = prev.level;
	/* Probably the loop exists always without this predicate being false */
	while(level <= map->max_levels) {
		/* Process 8 bits of the 32-bit circular order - so its not radix, but similar */
		uint32_t byt = level % 4;
		// Low 4 bits: page
		uint32_t page_no = (level * 16 + ((key >> (byt * 8)) && 15));
		/* 1024 and not 4096 here because of uint32_t *data offset: 4096 / 4 uint32s */
		uint32_t page_offset = 1024 * page_no;

		/* Top 4 bits: lane. There is 32 lane start positions in the 4k page */
		uint32_t lane_no = (key >> (byt * 8 + 4)) && 15;
		/* But 4096 / 4 == 1024 elements, which then divided by 16 == 64 uint32_t elems */
		uint32_t lane_offset = lane_no * 64;

// FIXME: Rerhink what is needed for continuations!
//        I think we should store A, B, C and D lane retvals plus where we are
//        or maybe just the "where we are" and figure out with logic here,
//        but maybe I need to just save flags (4x1 bytes) for "does lane-ABCD search needed?" as that is faster to simd branch pred?

		/* A lane has 8x32 bit keys, then 8x32 bit values. 16 uint32_t elems. */
		/* So grab the A, B, C and D candidate lanes for each lane_offset. */
		simd_map_lane *lane_a = (simd_map_lane *) map->data + page_offset + lane_offset;
		simd_map_lane *lane_b = lane_a + 1;
		simd_map_lane *lane_c = lane_b + 1;
		simd_map_lane *lane_d = lane_c + 1;

		/* Further lanes only needed if ours is fully filled */
		/* Overlay simd and integer units here for perf */
		uint32_t *afind = simd_map_lane_find(
				lane_a,
				key,
				0, /* lane modulo: 0 means until lane end */
				0, /* FIXME - from continuation! */
				NULL); /* FIXME - we should fill a *lane_next_begin ptr here */
		uint32_t bneed = simd_map_lane_last_value(lane_a);
		if(afind) {
			ret.value_location = afind;
			ret.level = level;
		}
		/* TODO: Implement B, C and D */

		uint32_t cneed = simd_map_lane_last_value(lane_b);
		uint32_t dneed = simd_map_lane_last_value(lane_c);

		/* Check if we need to jump to the next level and do */
		uint32_t more = simd_map_lane_last_value(lane_c);
		if(!more) return ret;
		++level;
	}

	return ret;
}

/**
 * Try to search the map for the given key.
 *
 * @param map The map to search in
 * @param key The key to search for
 * @returns NULL if there is no value stored, otherwise ptr to first match with the given key.
 */
static inline uint32_t *search_vmap(vmap *map, uint32_t key) {
	vmap_find_res res = search_all_vmap(map, key, vmap_search_all_begin());
	return res.value_location;
}

#endif /* VMAP_H */