1 files changed, 113 insertions, 0 deletions
diff --git a/src/lib/container/bloomfilt.c b/src/lib/container/bloomfilt.c
new file mode 100644
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+++ b/src/lib/container/bloomfilt.c
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+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file bloomfilt.c
+ * \brief Uses bitarray_t to implement a bloom filter.
+ **/
+
+#include <stdlib.h>
+
+#include "lib/malloc/malloc.h"
+#include "lib/container/bloomfilt.h"
+#include "lib/intmath/bits.h"
+#include "lib/log/util_bug.h"
+#include "siphash.h"
+
+/** How many bloom-filter bits we set per address. This is twice the
+ * BLOOMFILT_N_HASHES value, since we split the siphash output into two 32-bit
+ * values. */
+#define N_BITS_PER_ITEM (BLOOMFILT_N_HASHES * 2)
+
+struct bloomfilt_t {
+  /** siphash keys to make BLOOMFILT_N_HASHES independent hashes for each
+   * items. */
+  struct sipkey key[BLOOMFILT_N_HASHES];
+  bloomfilt_hash_fn hashfn; /**< Function used to generate hashes */
+  uint32_t mask; /**< One less than the number of bits in <b>ba</b>; always
+                  * one less than a power of two. */
+  bitarray_t *ba; /**< A bit array to implement the Bloom filter. */
+};
+
+#define BIT(set, n) ((n) & (set)->mask)
+
+/** Add the element <b>item</b> to <b>set</b>. */
+void
+bloomfilt_add(bloomfilt_t *set,
+              const void *item)
+{
+  int i;
+  for (i = 0; i < BLOOMFILT_N_HASHES; ++i) {
+    uint64_t h = set->hashfn(&set->key[i], item);
+    uint32_t high_bits = (uint32_t)(h >> 32);
+    uint32_t low_bits = (uint32_t)(h);
+    bitarray_set(set->ba, BIT(set, high_bits));
+    bitarray_set(set->ba, BIT(set, low_bits));
+  }
+}
+
+/** If <b>item</b> is in <b>set</b>, return nonzero.  Otherwise,
+ * <em>probably</em> return zero. */
+int
+bloomfilt_probably_contains(const bloomfilt_t *set,
+                            const void *item)
+{
+  int i, matches = 0;
+  for (i = 0; i < BLOOMFILT_N_HASHES; ++i) {
+    uint64_t h = set->hashfn(&set->key[i], item);
+    uint32_t high_bits = (uint32_t)(h >> 32);
+    uint32_t low_bits = (uint32_t)(h);
+    // Note that !! is necessary here, since bitarray_is_set does not
+    // necessarily return 1 on true.
+    matches += !! bitarray_is_set(set->ba, BIT(set, high_bits));
+    matches += !! bitarray_is_set(set->ba, BIT(set, low_bits));
+  }
+  return matches == N_BITS_PER_ITEM;
+}
+
+/** Return a newly allocated bloomfilt_t, optimized to hold a total of
+ * <b>max_elements</b> elements with a reasonably low false positive weight.
+ *
+ * Uses the siphash-based function <b>hashfn</b> to compute hard-to-collide
+ * functions of the items, and the key material <b>random_key</b> to
+ * key the hash.  There must be BLOOMFILT_KEY_LEN bytes in the supplied key.
+ **/
+bloomfilt_t *
+bloomfilt_new(int max_elements,
+              bloomfilt_hash_fn hashfn,
+              const uint8_t *random_key)
+{
+  /* The probability of false positives is about P=(1 - exp(-kn/m))^k, where k
+   * is the number of hash functions per entry, m is the bits in the array,
+   * and n is the number of elements inserted.  For us, k==4, n<=max_elements,
+   * and m==n_bits= approximately max_elements*32.  This gives
+   *   P<(1-exp(-4*n/(32*n)))^4 == (1-exp(1/-8))^4 == .00019
+   *
+   * It would be more optimal in space vs false positives to get this false
+   * positive rate by going for k==13, and m==18.5n, but we also want to
+   * conserve CPU, and k==13 is pretty big.
+   */
+  int n_bits = 1u << (tor_log2(max_elements)+5);
+  bloomfilt_t *r = tor_malloc(sizeof(bloomfilt_t));
+  r->mask = n_bits - 1;
+  r->ba = bitarray_init_zero(n_bits);
+
+  tor_assert(sizeof(r->key) == BLOOMFILT_KEY_LEN);
+  memcpy(r->key, random_key, sizeof(r->key));
+
+  r->hashfn = hashfn;
+
+  return r;
+}
+
+/** Free all storage held in <b>set</b>. */
+void
+bloomfilt_free_(bloomfilt_t *set)
+{
+  if (!set)
+    return;
+  bitarray_free(set->ba);
+  tor_free(set);
+}