Add internal hashing API designed for the typelib

In multiple places in the typelib, but most importantly the directory,
we need some fast indexing.  Perfect hashing, as implemented by CMPH
(previous commit), is an exact fit for the problem domain.

Add an API built on top of CMPH which maps strings->guint16 (we just
need a guint16 for the typelib index).

https://bugzilla.gnome.org/show_bug.cgi?id=554943

1 files changed, 210 insertions, 0 deletions

diff --git a/girepository/gthash.c b/girepository/gthash.c
new file mode 100644
index 00000000..5042ebe3
--- /dev/null
+++ b/girepository/gthash.c
@@ -0,0 +1,210 @@
+/* GObject introspection: Typelib hashing
+ *
+ * Copyright (C) 2010 Red Hat, 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.
+ */
+
+#include <glib.h>
+#include <glib-object.h>
+#include <string.h>
+
+#include "cmph/cmph.h"
+#include "gitypelib-internal.h"
+
+#define ALIGN_VALUE(this, boundary) \
+  (( ((unsigned long)(this)) + (((unsigned long)(boundary)) -1)) & (~(((unsigned long)(boundary))-1)))
+
+/**
+ * String hashing in the typelib.  We have a set of static (fixed) strings,
+ * and given one, we need to find its index number.  This problem is perfect
+ * hashing: http://en.wikipedia.org/wiki/Perfect_hashing
+ *
+ * I chose CMPH (http://cmph.sourceforge.net/) as it seemed high
+ * quality, well documented, and easy to embed.
+ *
+ * CMPH provides a number of algorithms; I chose BDZ, because while CHD
+ * appears to be the "best", the simplicitly of BDZ appealed, and really,
+ * we're only talking about thousands of strings here, not millions, so
+ * a few microseconds is no big deal.
+ *
+ * In memory, the format is:
+ * INT32 mph_size
+ * MPH (mph_size bytes)
+ * (padding for alignment to uint32 if necessary)
+ * INDEX (array of guint16)
+ *
+ * Because BDZ is not order preserving, we need a lookaside table which
+ * maps the hash value into the directory index.
+ */
+
+struct _GITypelibHashBuilder {
+  gboolean prepared;
+  gboolean buildable;
+  cmph_t *c;
+  GHashTable *strings;
+  guint32 dirmap_offset;
+  guint32 packed_size;
+};
+
+GITypelibHashBuilder *
+_gi_typelib_hash_builder_new (void)
+{
+  GITypelibHashBuilder *builder = g_slice_new0 (GITypelibHashBuilder);
+  builder->c = NULL;
+  builder->strings = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
+  return builder;
+}
+
+void
+_gi_typelib_hash_builder_add_string (GITypelibHashBuilder *builder,
+				     const char           *str,
+				     guint16               value)
+{
+  g_return_if_fail (builder->c == NULL);
+  g_hash_table_insert (builder->strings, g_strdup (str), GUINT_TO_POINTER ((guint) value));
+}
+
+gboolean
+_gi_typelib_hash_builder_prepare (GITypelibHashBuilder *builder)
+{
+  char **strs;
+  GHashTableIter hashiter;
+  gpointer key, value;
+  cmph_io_adapter_t *io;
+  cmph_config_t *config;
+  guint32 num_elts;
+  guint32 offset;
+  guint i;
+
+  if (builder->prepared)
+    return builder->buildable;
+  g_assert (builder->c == NULL);
+
+  num_elts = g_hash_table_size (builder->strings);
+  g_assert (num_elts <= 65536);
+
+  strs = (char**) g_new (char *, num_elts + 1);
+
+  i = 0;
+  g_hash_table_iter_init (&hashiter, builder->strings);
+  while (g_hash_table_iter_next (&hashiter, &key, &value))
+    {
+      const char *str = key;
+
+      strs[i++] = g_strdup (str);
+    }
+  strs[i++] = NULL;
+
+  io = cmph_io_vector_adapter (strs, num_elts);
+  config = cmph_config_new (io);
+  cmph_config_set_algo (config, CMPH_BDZ);
+
+  builder->c = cmph_new (config);
+  builder->prepared = TRUE;
+  if (!builder->c)
+    {
+      builder->buildable = FALSE;
+      goto out;
+    }
+  builder->buildable = TRUE;
+  g_assert (cmph_size (builder->c) == num_elts);
+
+  /* Pack a size counter at front */
+  offset = sizeof(guint32) + cmph_packed_size (builder->c);
+  builder->dirmap_offset = ALIGN_VALUE (offset, 4);
+  builder->packed_size = builder->dirmap_offset + (num_elts * sizeof(guint16));
+ out:
+  return builder->buildable;
+}
+
+guint32
+_gi_typelib_hash_builder_get_buffer_size (GITypelibHashBuilder *builder)
+{
+  g_return_val_if_fail (builder != NULL, 0);
+  g_return_val_if_fail (builder->prepared, 0);
+  g_return_val_if_fail (builder->buildable, 0 );
+
+  return builder->packed_size;
+}
+
+void
+_gi_typelib_hash_builder_pack (GITypelibHashBuilder *builder, guint8* mem, guint32 len)
+{
+  guint16 *table;
+  GHashTableIter hashiter;
+  gpointer key, value;
+  guint32 num_elts;
+  guint8 *packed_mem;
+
+  g_return_if_fail (builder != NULL);
+  g_return_if_fail (builder->prepared);
+  g_return_if_fail (builder->buildable);
+
+  g_assert (len >= builder->packed_size);
+  g_assert ((((unsigned long)mem) & 0x3) == 0);
+
+  *((guint32*) mem) = builder->dirmap_offset;
+  packed_mem = (guint8*)(mem + sizeof(guint32));
+  cmph_pack (builder->c, packed_mem);
+
+  table = (guint16*) (mem + builder->dirmap_offset);
+
+  num_elts = g_hash_table_size (builder->strings);
+  g_hash_table_iter_init (&hashiter, builder->strings);
+  while (g_hash_table_iter_next (&hashiter, &key, &value))
+    {
+      const char *str = key;
+      guint16 strval = (guint16)GPOINTER_TO_UINT(value);
+      guint32 hashv;
+
+      hashv = cmph_search_packed (packed_mem, str, strlen (str));
+      g_assert (hashv >= 0 && hashv < num_elts);
+      table[hashv] = strval;
+    }
+}
+
+void
+_gi_typelib_hash_builder_destroy (GITypelibHashBuilder *builder)
+{
+  if (builder->c)
+    {
+      cmph_destroy (builder->c);
+      builder->c = NULL;
+    }
+  g_hash_table_destroy (builder->strings);
+  g_slice_free (GITypelibHashBuilder, builder);
+}
+
+guint16
+_gi_typelib_hash_search (guint8* memory, const char *str)
+{
+  guint32 *mph;
+  guint16 *table;
+  guint32 dirmap_offset;
+  guint32 offset;
+
+  g_assert ((((unsigned long)memory) & 0x3) == 0);
+  mph = ((guint32*)memory)+1;
+
+  offset = cmph_search_packed (mph, str, strlen (str));
+
+  dirmap_offset = *((guint32*)memory);
+  table = (guint16*) (memory + dirmap_offset);
+
+  return table[offset];
+}
+