path: root/hashlib.c

/* hashlib.c -- functions to manage and access hash tables for bash. */

/* Copyright (C) 1987,1989,1991,1995,1998,2001,2003,2005,2006,2008,2009 Free Software Foundation, Inc.

   This file is part of GNU Bash, the Bourne Again SHell.

   Bash 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 3 of the License, or
   (at your option) any later version.

   Bash 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 Bash.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <config.h>

#include "bashansi.h"

#if defined (HAVE_UNISTD_H)
#  ifdef _MINIX
#    include <sys/types.h>
#  endif
#  include <unistd.h>
#endif

#include <stdio.h>

#include "shell.h"
#include "hashlib.h"

/* tunable constants for rehashing */
#define HASH_REHASH_MULTIPLIER	4
#define HASH_REHASH_FACTOR	2

#define HASH_SHOULDGROW(table) \
  ((table)->nentries >= (table)->nbuckets * HASH_REHASH_FACTOR)

/* an initial approximation */
#define HASH_SHOULDSHRINK(table) \
  (((table)->nbuckets > DEFAULT_HASH_BUCKETS) && \
   ((table)->nentries < (table)->nbuckets / HASH_REHASH_MULTIPLIER))

/* Rely on properties of unsigned division (unsigned/int -> unsigned) and
   don't discard the upper 32 bits of the value, if present. */
#define HASH_BUCKET(s, t, h) (((h) = hash_string (s)) & ((t)->nbuckets - 1))

static BUCKET_CONTENTS *copy_bucket_array PARAMS((BUCKET_CONTENTS *, sh_string_func_t *));

static void hash_rehash PARAMS((HASH_TABLE *, int));
static void hash_grow PARAMS((HASH_TABLE *));
static void hash_shrink PARAMS((HASH_TABLE *));

/* Make a new hash table with BUCKETS number of buckets.  Initialize
   each slot in the table to NULL. */
HASH_TABLE *
hash_create (buckets)
     int buckets;
{
  HASH_TABLE *new_table;
  register int i;

  new_table = (HASH_TABLE *)xmalloc (sizeof (HASH_TABLE));
  if (buckets == 0)
    buckets = DEFAULT_HASH_BUCKETS;

  new_table->bucket_array =
    (BUCKET_CONTENTS **)xmalloc (buckets * sizeof (BUCKET_CONTENTS *));
  new_table->nbuckets = buckets;
  new_table->nentries = 0;

  for (i = 0; i < buckets; i++)
    new_table->bucket_array[i] = (BUCKET_CONTENTS *)NULL;

  return (new_table);
}

int
hash_size (table)
     HASH_TABLE *table;
{
  return (HASH_ENTRIES(table));
}

static BUCKET_CONTENTS *
copy_bucket_array (ba, cpdata)
     BUCKET_CONTENTS *ba;
     sh_string_func_t *cpdata;	/* data copy function */
{
  BUCKET_CONTENTS *new_bucket, *n, *e;

  if (ba == 0)
    return ((BUCKET_CONTENTS *)0);

  for (n = (BUCKET_CONTENTS *)0, e = ba; e; e = e->next)
    {
      if (n == 0)
        {
          new_bucket = (BUCKET_CONTENTS *)xmalloc (sizeof (BUCKET_CONTENTS));
          n = new_bucket;
        }
      else
        {
          n->next = (BUCKET_CONTENTS *)xmalloc (sizeof (BUCKET_CONTENTS));
          n = n->next;
        }

      n->key = savestring (e->key);
      n->data = e->data ? (cpdata ? (*cpdata) (e->data) : savestring (e->data))
			: NULL;
      n->khash = e->khash;
      n->times_found = e->times_found;
      n->next = (BUCKET_CONTENTS *)NULL;
    }

  return new_bucket;  
}

static void
hash_rehash (table, nsize)
     HASH_TABLE *table;
     int nsize;
{
  int osize, i, j;
  BUCKET_CONTENTS **old_bucket_array, *item, *next;

  if (table == NULL || nsize == table->nbuckets)
    return;

  osize = table->nbuckets;
  old_bucket_array = table->bucket_array;

  table->nbuckets = nsize;
  table->bucket_array = (BUCKET_CONTENTS **)xmalloc (table->nbuckets * sizeof (BUCKET_CONTENTS *));
  for (i = 0; i < table->nbuckets; i++)
    table->bucket_array[i] = (BUCKET_CONTENTS *)NULL;

  for (j = 0; j < osize; j++)
    {
      for (item = old_bucket_array[j]; item; item = next)
	{
	  next = item->next;
	  i = item->khash & (table->nbuckets - 1);
	  item->next = table->bucket_array[i];
	  table->bucket_array[i] = item;
	}
    }

  free (old_bucket_array);
}

static void
hash_grow (table)
     HASH_TABLE *table;
{
  int nsize;

  nsize = table->nbuckets * HASH_REHASH_MULTIPLIER;
  if (nsize > 0)		/* overflow */
    hash_rehash (table, nsize);
}

static void
hash_shrink (table)
     HASH_TABLE *table;
{
  int nsize;

  nsize = table->nbuckets / HASH_REHASH_MULTIPLIER;
  hash_rehash (table, nsize);
}

HASH_TABLE *
hash_copy (table, cpdata)
     HASH_TABLE *table;
     sh_string_func_t *cpdata;
{
  HASH_TABLE *new_table;
  int i;

  if (table == 0)
    return ((HASH_TABLE *)NULL);

  new_table = hash_create (table->nbuckets);

  for (i = 0; i < table->nbuckets; i++)
    new_table->bucket_array[i] = copy_bucket_array (table->bucket_array[i], cpdata);

  new_table->nentries = table->nentries;
  return new_table;
}

/* This is the best 32-bit string hash function I found. It's one of the
   Fowler-Noll-Vo family (FNV-1).

   The magic is in the interesting relationship between the special prime
   16777619 (2^24 + 403) and 2^32 and 2^8. */

#define FNV_OFFSET 2166136261
#define FNV_PRIME 16777619

/* If you want to use 64 bits, use
FNV_OFFSET	14695981039346656037
FNV_PRIME	1099511628211
*/

/* The `khash' check below requires that strings that compare equally with
   strcmp hash to the same value. */
unsigned int
hash_string (s)
     const char *s;
{
  register unsigned int i;

  for (i = FNV_OFFSET; *s; s++)
    {
      /* FNV-1a has the XOR first, traditional FNV-1 has the multiply first */

      /* was i *= FNV_PRIME */
      i += (i<<1) + (i<<4) + (i<<7) + (i<<8) + (i<<24);
      i ^= *s;
    }

  return i;
}

/* Return the location of the bucket which should contain the data
   for STRING.  TABLE is a pointer to a HASH_TABLE. */

int
hash_bucket (string, table)
     const char *string;
     HASH_TABLE *table;
{
  unsigned int h;

  return (HASH_BUCKET (string, table, h));
}

/* Return a pointer to the hashed item.  If the HASH_CREATE flag is passed,
   create a new hash table entry for STRING, otherwise return NULL. */
BUCKET_CONTENTS *
hash_search (string, table, flags)
     const char *string;
     HASH_TABLE *table;
     int flags;
{
  BUCKET_CONTENTS *list;
  int bucket;
  unsigned int hv;

  if (table == 0 || ((flags & HASH_CREATE) == 0 && HASH_ENTRIES (table) == 0))
    return (BUCKET_CONTENTS *)NULL;

  bucket = HASH_BUCKET (string, table, hv);

  for (list = table->bucket_array ? table->bucket_array[bucket] : 0; list; list = list->next)
    {
      /* This is the comparison function */
      if (hv == list->khash && STREQ (list->key, string))
	{
	  list->times_found++;
	  return (list);
	}
    }

  if (flags & HASH_CREATE)
    {
      if (HASH_SHOULDGROW (table))
	{
	  hash_grow (table);
	  bucket = HASH_BUCKET (string, table, hv);
	}

      list = (BUCKET_CONTENTS *)xmalloc (sizeof (BUCKET_CONTENTS));
      list->next = table->bucket_array[bucket];
      table->bucket_array[bucket] = list;

      list->data = NULL;
      list->key = (char *)string;	/* XXX fix later */
      list->khash = hv;
      list->times_found = 0;

      table->nentries++;
      return (list);
    }
      
  return (BUCKET_CONTENTS *)NULL;
}

/* Remove the item specified by STRING from the hash table TABLE.
   The item removed is returned, so you can free its contents.  If
   the item isn't in this table NULL is returned. */
BUCKET_CONTENTS *
hash_remove (string, table, flags)
     const char *string;
     HASH_TABLE *table;
     int flags;
{
  int bucket;
  BUCKET_CONTENTS *prev, *temp;
  unsigned int hv;

  if (table == 0 || HASH_ENTRIES (table) == 0)
    return (BUCKET_CONTENTS *)NULL;

  bucket = HASH_BUCKET (string, table, hv);
  prev = (BUCKET_CONTENTS *)NULL;
  for (temp = table->bucket_array[bucket]; temp; temp = temp->next)
    {
      if (hv == temp->khash && STREQ (temp->key, string))
	{
	  if (prev)
	    prev->next = temp->next;
	  else
	    table->bucket_array[bucket] = temp->next;

	  table->nentries--;
	  return (temp);
	}
      prev = temp;
    }
  return ((BUCKET_CONTENTS *) NULL);
}

/* Create an entry for STRING, in TABLE.  If the entry already
   exists, then return it (unless the HASH_NOSRCH flag is set). */
BUCKET_CONTENTS *
hash_insert (string, table, flags)
     char *string;
     HASH_TABLE *table;
     int flags;
{
  BUCKET_CONTENTS *item;
  int bucket;
  unsigned int hv;

  if (table == 0)
    table = hash_create (0);

  item = (flags & HASH_NOSRCH) ? (BUCKET_CONTENTS *)NULL
  			       : hash_search (string, table, 0);

  if (item == 0)
    {
      if (HASH_SHOULDGROW (table))
	hash_grow (table);

      bucket = HASH_BUCKET (string, table, hv);

      item = (BUCKET_CONTENTS *)xmalloc (sizeof (BUCKET_CONTENTS));
      item->next = table->bucket_array[bucket];
      table->bucket_array[bucket] = item;

      item->data = NULL;
      item->key = string;
      item->khash = hv;
      item->times_found = 0;

      table->nentries++;
    }

  return (item);
}

/* Remove and discard all entries in TABLE.  If FREE_DATA is non-null, it
   is a function to call to dispose of a hash item's data.  Otherwise,
   free() is called. */
void
hash_flush (table, free_data)
     HASH_TABLE *table;
     sh_free_func_t *free_data;
{
  int i;
  register BUCKET_CONTENTS *bucket, *item;

  if (table == 0 || HASH_ENTRIES (table) == 0)
    return;

  for (i = 0; i < table->nbuckets; i++)
    {
      bucket = table->bucket_array[i];

      while (bucket)
	{
	  item = bucket;
	  bucket = bucket->next;

	  if (free_data)
	    (*free_data) (item->data);
	  else
	    free (item->data);
	  free (item->key);
	  free (item);
	}
      table->bucket_array[i] = (BUCKET_CONTENTS *)NULL;
    }

  table->nentries = 0;
}

/* Free the hash table pointed to by TABLE. */
void
hash_dispose (table)
     HASH_TABLE *table;
{
  free (table->bucket_array);
  free (table);
}

void
hash_walk (table, func)
     HASH_TABLE *table;
     hash_wfunc *func;
{
  register int i;
  BUCKET_CONTENTS *item;

  if (table == 0 || HASH_ENTRIES (table) == 0)
    return;

  for (i = 0; i < table->nbuckets; i++)
    {
      for (item = hash_items (i, table); item; item = item->next)
	if ((*func) (item) < 0)
	  return;
    }
}

#if defined (DEBUG) || defined (TEST_HASHING)
void
hash_pstats (table, name)
     HASH_TABLE *table;
     char *name;
{
  register int slot, bcount;
  register BUCKET_CONTENTS *bc;

  if (name == 0)
    name = "unknown hash table";

  fprintf (stderr, "%s: %d buckets; %d items\n", name, table->nbuckets, table->nentries);

  /* Print out a count of how many strings hashed to each bucket, so we can
     see how even the distribution is. */
  for (slot = 0; slot < table->nbuckets; slot++)
    {
      bc = hash_items (slot, table);

      fprintf (stderr, "\tslot %3d: ", slot);
      for (bcount = 0; bc; bc = bc->next)
	bcount++;

      fprintf (stderr, "%d\n", bcount);
    }
}
#endif

#ifdef TEST_HASHING

/* link with xmalloc.o and lib/malloc/libmalloc.a */
#undef NULL
#include <stdio.h>

#ifndef NULL
#define NULL 0
#endif

HASH_TABLE *table, *ntable;

int interrupt_immediately = 0;
int running_trap = 0;

int
signal_is_trapped (s)
     int s;
{
  return (0);
}

void
programming_error (const char *format, ...)
{
  abort();
}

void
fatal_error (const char *format, ...)
{
  abort();
}

void
internal_warning (const char *format, ...)
{
}

int
main ()
{
  char string[256];
  int count = 0;
  BUCKET_CONTENTS *tt;

#if defined (TEST_NBUCKETS)
  table = hash_create (TEST_NBUCKETS);
#else
  table = hash_create (0);
#endif

  for (;;)
    {
      char *temp_string;
      if (fgets (string, sizeof (string), stdin) == 0)
	break;
      if (!*string)
	break;
      temp_string = savestring (string);
      tt = hash_insert (temp_string, table, 0);
      if (tt->times_found)
	{
	  fprintf (stderr, "You have already added item `%s'\n", string);
	  free (temp_string);
	}
      else
	{
	  count++;
	}
    }

  hash_pstats (table, "hash test");

  ntable = hash_copy (table, (sh_string_func_t *)NULL);
  hash_flush (table, (sh_free_func_t *)NULL);
  hash_pstats (ntable, "hash copy test");

  exit (0);
}

#endif /* TEST_HASHING */