lib/bloom: Add an internal bloom filter implementation

This will be used in an upcoming commit. It adds a basic bloom filter
implementation, using the SipHash family of hash functions.

The implementation (including its parameter choices and hash functions)
will become a protocol detail in future, so must not be changed so that
its output is bitwise incompatible between OSTree versions.

Unit tests are included.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #924
Approved by: cgwalters

src/libostree/ostree-bloom-private.h

@@ -0,0 +1,104 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright © 2017 Endless Mobile, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Authors:
+ *  - Philip Withnall <withnall@endlessm.com>
+ */
+
+#pragma once
+
+#include <gio/gio.h>
+#include <glib.h>
+#include <glib-object.h>
+
+G_BEGIN_DECLS
+
+/**
+ * OstreeBloom:
+ *
+ * An implementation of a [bloom filter](https://en.wikipedia.org/wiki/Bloom_filter)
+ * which is suitable for building a filter and looking keys up in an existing
+ * filter.
+ *
+ * Since: 2017.8
+ */
+typedef struct _OstreeBloom OstreeBloom;
+
+/**
+ * OstreeBloomHashFunc:
+ * @element: a pointer to the element to hash
+ * @k: hash function parameter
+ *
+ * Function prototype for a
+ * [universal hash function](https://en.wikipedia.org/wiki/Universal_hashing),
+ * parameterised on @k, which hashes @element to a #guint64 hash value.
+ *
+ * It is up to the implementer of the hash function whether %NULL is valid for
+ * @element.
+ *
+ * Since: 2017.8
+ */
+typedef guint64 (*OstreeBloomHashFunc) (gconstpointer element,
+                                        guint8        k);
+
+#define OSTREE_TYPE_BLOOM (ostree_bloom_get_type ())
+
+G_GNUC_INTERNAL
+GType ostree_bloom_get_type (void);
+
+G_GNUC_INTERNAL
+OstreeBloom *ostree_bloom_new (gsize               n_bytes,
+                               guint8              k,
+                               OstreeBloomHashFunc hash_func);
+
+G_GNUC_INTERNAL
+OstreeBloom *ostree_bloom_new_from_bytes (GBytes              *bytes,
+                                          guint8               k,
+                                          OstreeBloomHashFunc  hash_func);
+
+G_GNUC_INTERNAL
+OstreeBloom *ostree_bloom_ref (OstreeBloom *bloom);
+G_GNUC_INTERNAL
+void ostree_bloom_unref (OstreeBloom *bloom);
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeBloom, ostree_bloom_unref)
+
+G_GNUC_INTERNAL
+gboolean ostree_bloom_maybe_contains (OstreeBloom   *bloom,
+                                      gconstpointer  element);
+
+G_GNUC_INTERNAL
+GBytes *ostree_bloom_seal (OstreeBloom *bloom);
+
+G_GNUC_INTERNAL
+void ostree_bloom_add_element (OstreeBloom   *bloom,
+                               gconstpointer  element);
+
+G_GNUC_INTERNAL
+gsize ostree_bloom_get_size (OstreeBloom *bloom);
+G_GNUC_INTERNAL
+guint8 ostree_bloom_get_k (OstreeBloom *bloom);
+G_GNUC_INTERNAL
+OstreeBloomHashFunc ostree_bloom_get_hash_func (OstreeBloom *bloom);
+
+G_GNUC_INTERNAL
+guint64 ostree_str_bloom_hash (gconstpointer element,
+                               guint8        k);
+
+G_END_DECLS