glib/gthash.c

/* 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];
}