bbf.c

#include <stdlib.h>
#include <string.h>
#include "yak.h"

yak_bf_t *yak_bf_init(int n_shift, int n_hashes)
{
	yak_bf_t *b;
	void *ptr = 0;
	if (n_shift + YAK_BLK_SHIFT > 64 || n_shift < YAK_BLK_SHIFT) return 0;
	b = calloc(1, sizeof(yak_bf_t));
	b->n_shift = n_shift;
	b->n_hashes = n_hashes;
	posix_memalign(&ptr, 1<<(YAK_BLK_SHIFT-3), 1ULL<<(n_shift-3));
	b->b = ptr;
	bzero(b->b, 1ULL<<(n_shift-3));
	return b;
}

void yak_bf_destroy(yak_bf_t *b)
{
	if (b == 0) return;
	free(b->b); free(b);
}

int yak_bf_insert(yak_bf_t *b, uint64_t hash)
{
	int x = b->n_shift - YAK_BLK_SHIFT;
	uint64_t y = hash & ((1ULL<<x) - 1);
	int h1 = hash >> x & YAK_BLK_MASK;
	int h2 = hash >> b->n_shift & YAK_BLK_MASK;
	uint8_t *p = &b->b[y<<(YAK_BLK_SHIFT-3)];
	int i, z = h1, cnt = 0;
	if ((h2&31) == 0) h2 = (h2 + 1) & YAK_BLK_MASK; // otherwise we may repeatedly use a few bits
	for (i = 0; i < b->n_hashes; z = (z + h2) & YAK_BLK_MASK) {
		uint8_t *q = &p[z>>3], u;
		u = 1<<(z&7);
		cnt += !!(*q & u);
		*q |= u;
		++i;
	}
	return cnt;
}