hash.c

GNU的词法/语法分析器bison源码

/* hash - hashing table processing.

   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004 Free
   Software Foundation, Inc.

   Written by Jim Meyering, 1992.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* A generic hash table package.  */

/* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead
   of malloc.  If you change USE_OBSTACK, you have to recompile!  */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include "hash.h"
#include "xalloc.h"

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>

#if USE_OBSTACK
# include "obstack.h"
# ifndef obstack_chunk_alloc
#  define obstack_chunk_alloc malloc
# endif
# ifndef obstack_chunk_free
#  define obstack_chunk_free free
# endif
#endif

#ifndef SIZE_MAX
# define SIZE_MAX ((size_t) -1)
#endif

struct hash_table
  {
    /* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1,
       for a possibility of N_BUCKETS.  Among those, N_BUCKETS_USED buckets
       are not empty, there are N_ENTRIES active entries in the table.  */
    struct hash_entry *bucket;
    struct hash_entry const *bucket_limit;
    size_t n_buckets;
    size_t n_buckets_used;
    size_t n_entries;

    /* Tuning arguments, kept in a physicaly separate structure.  */
    const Hash_tuning *tuning;

    /* Three functions are given to `hash_initialize', see the documentation
       block for this function.  In a word, HASHER randomizes a user entry
       into a number up from 0 up to some maximum minus 1; COMPARATOR returns
       true if two user entries compare equally; and DATA_FREER is the cleanup
       function for a user entry.  */
    Hash_hasher hasher;
    Hash_comparator comparator;
    Hash_data_freer data_freer;

    /* A linked list of freed struct hash_entry structs.  */
    struct hash_entry *free_entry_list;

#if USE_OBSTACK
    /* Whenever obstacks are used, it is possible to allocate all overflowed
       entries into a single stack, so they all can be freed in a single
       operation.  It is not clear if the speedup is worth the trouble.  */
    struct obstack entry_stack;
#endif
  };

/* A hash table contains many internal entries, each holding a pointer to
   some user provided data (also called a user entry).  An entry indistinctly
   refers to both the internal entry and its associated user entry.  A user
   entry contents may be hashed by a randomization function (the hashing
   function, or just `hasher' for short) into a number (or `slot') between 0
   and the current table size.  At each slot position in the hash table,
   starts a linked chain of entries for which the user data all hash to this
   slot.  A bucket is the collection of all entries hashing to the same slot.

   A good `hasher' function will distribute entries rather evenly in buckets.
   In the ideal case, the length of each bucket is roughly the number of
   entries divided by the table size.  Finding the slot for a data is usually
   done in constant time by the `hasher', and the later finding of a precise
   entry is linear in time with the size of the bucket.  Consequently, a
   larger hash table size (that is, a larger number of buckets) is prone to
   yielding shorter chains, *given* the `hasher' function behaves properly.

   Long buckets slow down the lookup algorithm.  One might use big hash table
   sizes in hope to reduce the average length of buckets, but this might
   become inordinate, as unused slots in the hash table take some space.  The
   best bet is to make sure you are using a good `hasher' function (beware
   that those are not that easy to write! :-), and to use a table size
   larger than the actual number of entries.  */

/* If an insertion makes the ratio of nonempty buckets to table size larger
   than the growth threshold (a number between 0.0 and 1.0), then increase
   the table size by multiplying by the growth factor (a number greater than
   1.0).  The growth threshold defaults to 0.8, and the growth factor
   defaults to 1.414, meaning that the table will have doubled its size
   every second time 80% of the buckets get used.  */
#define DEFAULT_GROWTH_THRESHOLD 0.8
#define DEFAULT_GROWTH_FACTOR 1.414

/* If a deletion empties a bucket and causes the ratio of used buckets to
   table size to become smaller than the shrink threshold (a number between
   0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a
   number greater than the shrink threshold but smaller than 1.0).  The shrink
   threshold and factor default to 0.0 and 1.0, meaning that the table never
   shrinks.  */
#define DEFAULT_SHRINK_THRESHOLD 0.0
#define DEFAULT_SHRINK_FACTOR 1.0

/* Use this to initialize or reset a TUNING structure to
   some sensible values. */
static const Hash_tuning default_tuning =
  {
    DEFAULT_SHRINK_THRESHOLD,
    DEFAULT_SHRINK_FACTOR,
    DEFAULT_GROWTH_THRESHOLD,
    DEFAULT_GROWTH_FACTOR,
    false
  };

/* Information and lookup.  */

/* The following few functions provide information about the overall hash
   table organization: the number of entries, number of buckets and maximum
   length of buckets.  */

/* Return the number of buckets in the hash table.  The table size, the total
   number of buckets (used plus unused), or the maximum number of slots, are
   the same quantity.  */

size_t
hash_get_n_buckets (const Hash_table *table)
{
  return table->n_buckets;
}

/* Return the number of slots in use (non-empty buckets).  */

size_t
hash_get_n_buckets_used (const Hash_table *table)
{
  return table->n_buckets_used;
}

/* Return the number of active entries.  */

size_t
hash_get_n_entries (const Hash_table *table)
{
  return table->n_entries;
}

/* Return the length of the longest chain (bucket).  */

size_t
hash_get_max_bucket_length (const Hash_table *table)
{
  struct hash_entry const *bucket;
  size_t max_bucket_length = 0;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
    {
      if (bucket->data)
	{
	  struct hash_entry const *cursor = bucket;
	  size_t bucket_length = 1;

	  while (cursor = cursor->next, cursor)
	    bucket_length++;

	  if (bucket_length > max_bucket_length)
	    max_bucket_length = bucket_length;
	}
    }

  return max_bucket_length;
}

/* Do a mild validation of a hash table, by traversing it and checking two
   statistics.  */

bool
hash_table_ok (const Hash_table *table)
{
  struct hash_entry const *bucket;
  size_t n_buckets_used = 0;
  size_t n_entries = 0;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
    {
      if (bucket->data)
	{
	  struct hash_entry const *cursor = bucket;

	  /* Count bucket head.  */
	  n_buckets_used++;
	  n_entries++;

	  /* Count bucket overflow.  */
	  while (cursor = cursor->next, cursor)
	    n_entries++;
	}
    }

  if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries)
    return true;

  return false;
}

void
hash_print_statistics (const Hash_table *table, FILE *stream)
{
  size_t n_entries = hash_get_n_entries (table);
  size_t n_buckets = hash_get_n_buckets (table);
  size_t n_buckets_used = hash_get_n_buckets_used (table);
  size_t max_bucket_length = hash_get_max_bucket_length (table);

  fprintf (stream, "# entries:         %lu\n", (unsigned long int) n_entries);
  fprintf (stream, "# buckets:         %lu\n", (unsigned long int) n_buckets);
  fprintf (stream, "# buckets used:    %lu (%.2f%%)\n",
	   (unsigned long int) n_buckets_used,
	   (100.0 * n_buckets_used) / n_buckets);
  fprintf (stream, "max bucket length: %lu\n",
	   (unsigned long int) max_bucket_length);
}

/* If ENTRY matches an entry already in the hash table, return the
   entry from the table.  Otherwise, return NULL.  */

void *
hash_lookup (const Hash_table *table, const void *entry)
{
  struct hash_entry const *bucket
    = table->bucket + table->hasher (entry, table->n_buckets);
  struct hash_entry const *cursor;

  if (! (bucket < table->bucket_limit))
    abort ();

  if (bucket->data == NULL)
    return NULL;

  for (cursor = bucket; cursor; cursor = cursor->next)
    if (table->comparator (entry, cursor->data))
      return cursor->data;

  return NULL;
}

/* Walking.  */

/* The functions in this page traverse the hash table and process the
   contained entries.  For the traversal to work properly, the hash table
   should not be resized nor modified while any particular entry is being
   processed.  In particular, entries should not be added or removed.  */

/* Return the first data in the table, or NULL if the table is empty.  */

void *
hash_get_first (const Hash_table *table)
{
  struct hash_entry const *bucket;

  if (table->n_entries == 0)
    return NULL;

  for (bucket = table->bucket; ; bucket++)
    if (! (bucket < table->bucket_limit))
      abort ();
    else if (bucket->data)
      return bucket->data;
}

/* Return the user data for the entry following ENTRY, where ENTRY has been
   returned by a previous call to either `hash_get_first' or `hash_get_next'.
   Return NULL if there are no more entries.  */

void *
hash_get_next (const Hash_table *table, const void *entry)
{
  struct hash_entry const *bucket
    = table->bucket + table->hasher (entry, table->n_buckets);
  struct hash_entry const *cursor;

  if (! (bucket < table->bucket_limit))
    abort ();

  /* Find next entry in the same bucket.  */
  for (cursor = bucket; cursor; cursor = cursor->next)
    if (cursor->data == entry && cursor->next)
      return cursor->next->data;

  /* Find first entry in any subsequent bucket.  */
  while (++bucket < table->bucket_limit)
    if (bucket->data)
      return bucket->data;

  /* None found.  */
  return NULL;
}

/* Fill BUFFER with pointers to active user entries in the hash table, then
   return the number of pointers copied.  Do not copy more than BUFFER_SIZE
   pointers.  */

size_t
hash_get_entries (const Hash_table *table, void **buffer,
		  size_t buffer_size)
{
  size_t counter = 0;
  struct hash_entry const *bucket;
  struct hash_entry const *cursor;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
    {
      if (bucket->data)
	{
	  for (cursor = bucket; cursor; cursor = cursor->next)
	    {
	      if (counter >= buffer_size)
		return counter;
	      buffer[counter++] = cursor->data;
	    }
	}
    }

  return counter;
}

/* Call a PROCESSOR function for each entry of a hash table, and return the
   number of entries for which the processor function returned success.  A
   pointer to some PROCESSOR_DATA which will be made available to each call to
   the processor function.  The PROCESSOR accepts two arguments: the first is
   the user entry being walked into, the second is the value of PROCESSOR_DATA
   as received.  The walking continue for as long as the PROCESSOR function
   returns nonzero.  When it returns zero, the walking is interrupted.  */

size_t
hash_do_for_each (const Hash_table *table, Hash_processor processor,
		  void *processor_data)
{
  size_t counter = 0;
  struct hash_entry const *bucket;
  struct hash_entry const *cursor;

  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
    {
      if (bucket->data)
	{
	  for (cursor = bucket; cursor; cursor = cursor->next)
	    {
	      if (!(*processor) (cursor->data, processor_data))
		return counter;
	      counter++;
	    }
	}
    }

  return counter;
}

/* Allocation and clean-up.  */

/* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
   This is a convenience routine for constructing other hashing functions.  */

#if USE_DIFF_HASH

/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
   B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
   Software--practice & experience 20, 2 (Feb 1990), 209-224.  Good hash
   algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
   may not be good for your application."  */

size_t
hash_string (const char *string, size_t n_buckets)
{
# define ROTATE_LEFT(Value, Shift) \
  ((Value) << (Shift) | (Value) >> ((sizeof (size_t) * CHAR_BIT) - (Shift)))
# define HASH_ONE_CHAR(Value, Byte) \
  ((Byte) + ROTATE_LEFT (Value, 7))

  size_t value = 0;
  unsigned char ch;

  for (; (ch = *string); string++)
    value = HASH_ONE_CHAR (value, ch);
  return value % n_buckets;

# undef ROTATE_LEFT
# undef HASH_ONE_CHAR
}

#else /* not USE_DIFF_HASH */

/* This one comes from `recode', and performs a bit better than the above as
   per a few experiments.  It is inspired from a hashing routine found in the
   very old Cyber `snoop', itself written in typical Greg Mansfield style.
   (By the way, what happened to this excellent man?  Is he still alive?)  */

size_t
hash_string (const char *string, size_t n_buckets)
{
  size_t value = 0;
  unsigned char ch;

  for (; (ch = *string); string++)
    value = (value * 31 + ch) % n_buckets;
  return value;
}

#endif /* not USE_DIFF_HASH */

/* Return true if CANDIDATE is a prime number.  CANDIDATE should be an odd
   number at least equal to 11.  */

static bool
is_prime (size_t candidate)
{
  size_t divisor = 3;
  size_t square = divisor * divisor;

  while (square < candidate && (candidate % divisor))
    {
      divisor++;
      square += 4 * divisor;
      divisor++;
    }

  return (candidate % divisor ? true : false);
}

/* Round a given CANDIDATE number up to the nearest prime, and return that
   prime.  Primes lower than 10 are merely skipped.  */

static size_t
next_prime (size_t candidate)
{
  /* Skip small primes.  */
  if (candidate < 10)
    candidate = 10;

  /* Make it definitely odd.  */
  candidate |= 1;

  while (!is_prime (candidate))
    candidate += 2;

  return candidate;
}

void
hash_reset_tuning (Hash_tuning *tuning)
{
  *tuning = default_tuning;
}

/* For the given hash TABLE, check the user supplied tuning structure for
   reasonable values, and return true if there is no gross error with it.
   Otherwise, definitively reset the TUNING field to some acceptable default
   in the hash table (that is, the user loses the right of further modifying
   tuning arguments), and return false.  */

static bool
check_tuning (Hash_table *table)
{
  const Hash_tuning *tuning = table->tuning;

  /* Be a bit stricter than mathematics would require, so that
     rounding errors in size calculations do not cause allocations to
     fail to grow or shrink as they should.  The smallest allocation
     is 11 (due to next_prime's algorithm), so an epsilon of 0.1
     should be good enough.  */
  float epsilon = 0.1f;

  if (epsilon < tuning->growth_threshold
      && tuning->growth_threshold < 1 - epsilon
      && 1 + epsilon < tuning->growth_factor
      && 0 <= tuning->shrink_threshold
      && tuning->shrink_threshold + epsilon < tuning->shrink_factor
      && tuning->shrink_factor <= 1
      && tuning->shrink_threshold + epsilon < tuning->growth_threshold)
    return true;

  table->tuning = &default_tuning;
  return false;
}

/* Allocate and return a new hash table, or NULL upon failure.  The initial
   number of buckets is automatically selected so as to _guarantee_ that you
   may insert at least CANDIDATE different user entries before any growth of
   the hash table size occurs.  So, if have a reasonably tight a-priori upper
   bound on the number of entries you intend to insert in the hash table, you
   may save some table memory and insertion time, by specifying it here.  If
   the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
   argument has its meaning changed to the wanted number of buckets.

   TUNING points to a structure of user-supplied values, in case some fine
   tuning is wanted over the default behavior of the hasher.  If TUNING is
   NULL, the default tuning parameters are used instead.

   The user-supplied HASHER function should be provided.  It accepts two
   arguments ENTRY and TABLE_SIZE.  It computes, by hashing ENTRY contents, a
   slot number for that entry which should be in the range 0..TABLE_SIZE-1.
   This slot number is then returned.

   The user-supplied COMPARATOR function should be provided.  It accepts two