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205 lines (160 loc) · 4.27 KB
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/* Licensed under BSD-MIT - see LICENSE file for details */
#include "invbloom.h"
#include <ccan/hash/hash.h>
#include <ccan/endian/endian.h>
#include <assert.h>
/* "We will show that hash_count values of 3 or 4 work well in practice"
From:
Eppstein, David, et al. "What's the difference?: efficient set reconciliation without prior context." ACM SIGCOMM Computer Communication Review. Vol. 41. No. 4. ACM, 2011. http://conferences.sigcomm.org/sigcomm/2011/papers/sigcomm/p218.pdf
*/
#define NUM_HASHES 3
struct invbloom *invbloom_new_(const tal_t *ctx,
size_t id_size,
size_t n_elems,
u32 salt)
{
struct invbloom *ib = tal(ctx, struct invbloom);
if (ib) {
ib->n_elems = n_elems;
ib->id_size = id_size;
ib->salt = salt;
ib->singleton = NULL;
ib->count = tal_arrz(ib, s32, n_elems);
ib->idsum = tal_arrz(ib, u8, id_size * n_elems);
if (!ib->count || !ib->idsum)
ib = tal_free(ib);
}
return ib;
}
void invbloom_singleton_cb_(struct invbloom *ib,
void (*cb)(struct invbloom *,
size_t bucket, bool, void *),
void *data)
{
ib->singleton = cb;
ib->singleton_data = data;
}
static size_t hash_bucket(const struct invbloom *ib, const void *id, size_t i)
{
return hash((const char *)id, ib->id_size, ib->salt+i*7) % ib->n_elems;
}
static u8 *idsum_ptr(const struct invbloom *ib, size_t bucket)
{
return (u8 *)ib->idsum + bucket * ib->id_size;
}
static void check_for_singleton(struct invbloom *ib, size_t bucket, bool before)
{
if (!ib->singleton)
return;
if (ib->count[bucket] != 1 && ib->count[bucket] != -1)
return;
ib->singleton(ib, bucket, before, ib->singleton_data);
}
static void add_to_bucket(struct invbloom *ib, size_t n, const u8 *id)
{
size_t i;
u8 *idsum = idsum_ptr(ib, n);
check_for_singleton(ib, n, true);
ib->count[n]++;
for (i = 0; i < ib->id_size; i++)
idsum[i] ^= id[i];
check_for_singleton(ib, n, false);
}
static void remove_from_bucket(struct invbloom *ib, size_t n, const u8 *id)
{
size_t i;
u8 *idsum = idsum_ptr(ib, n);
check_for_singleton(ib, n, true);
ib->count[n]--;
for (i = 0; i < ib->id_size; i++)
idsum[i] ^= id[i];
check_for_singleton(ib, n, false);
}
void invbloom_insert(struct invbloom *ib, const void *id)
{
unsigned int i;
for (i = 0; i < NUM_HASHES; i++)
add_to_bucket(ib, hash_bucket(ib, id, i), id);
}
void invbloom_delete(struct invbloom *ib, const void *id)
{
unsigned int i;
for (i = 0; i < NUM_HASHES; i++)
remove_from_bucket(ib, hash_bucket(ib, id, i), id);
}
static bool all_zero(const u8 *mem, size_t size)
{
unsigned int i;
for (i = 0; i < size; i++)
if (mem[i])
return false;
return true;
}
bool invbloom_get(const struct invbloom *ib, const void *id)
{
unsigned int i;
for (i = 0; i < NUM_HASHES; i++) {
size_t h = hash_bucket(ib, id, i);
u8 *idsum = idsum_ptr(ib, h);
if (ib->count[h] == 0 && all_zero(idsum, ib->id_size))
return false;
if (ib->count[h] == 1)
return (memcmp(idsum, id, ib->id_size) == 0);
}
return false;
}
static void *extract(const tal_t *ctx, struct invbloom *ib, int count)
{
size_t i;
/* FIXME: this makes full extraction O(n^2). */
for (i = 0; i < ib->n_elems; i++) {
void *id;
if (ib->count[i] != count)
continue;
id = tal_dup_arr(ctx, u8, idsum_ptr(ib, i), ib->id_size, 0);
return id;
}
return NULL;
}
void *invbloom_extract(const tal_t *ctx, struct invbloom *ib)
{
void *id;
id = extract(ctx, ib, 1);
if (id)
invbloom_delete(ib, id);
return id;
}
void *invbloom_extract_negative(const tal_t *ctx, struct invbloom *ib)
{
void *id;
id = extract(ctx, ib, -1);
if (id)
invbloom_insert(ib, id);
return id;
}
void invbloom_subtract(struct invbloom *ib1, const struct invbloom *ib2)
{
size_t i;
assert(ib1->n_elems == ib2->n_elems);
assert(ib1->id_size == ib2->id_size);
assert(ib1->salt == ib2->salt);
for (i = 0; i < ib1->n_elems; i++)
check_for_singleton(ib1, i, true);
for (i = 0; i < ib1->n_elems * ib1->id_size; i++)
ib1->idsum[i] ^= ib2->idsum[i];
for (i = 0; i < ib1->n_elems; i++) {
ib1->count[i] -= ib2->count[i];
check_for_singleton(ib1, i, false);
}
}
bool invbloom_empty(const struct invbloom *ib)
{
size_t i;
for (i = 0; i < ib->n_elems; i++) {
if (ib->count[i])
return false;
if (!all_zero(idsum_ptr(ib, i), ib->id_size))
return false;
}
return true;
}