XEmacs 21.2.14.

[chise/xemacs-chise.git.1] / src / elhash.c

/* Implementation of the hash table lisp object type.
   Copyright (C) 1992, 1993, 1994 Free Software Foundation, Inc.
   Copyright (C) 1995, 1996 Ben Wing.
   Copyright (C) 1997 Free Software Foundation, Inc.

This file is part of XEmacs.

XEmacs 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.

XEmacs is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCNTABILITY 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 XEmacs; see the file COPYING.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* Synched up with: Not in FSF. */

#include <config.h>
#include "lisp.h"
#include "bytecode.h"
#include "elhash.h"

Lisp_Object Qhash_tablep, Qhashtable, Qhash_table;
Lisp_Object Qweak, Qkey_weak, Qvalue_weak, Qnon_weak;
static Lisp_Object Vall_weak_hash_tables;
static Lisp_Object Qrehash_size, Qrehash_threshold;
static Lisp_Object Q_size, Q_test, Q_type, Q_rehash_size, Q_rehash_threshold;

typedef struct hentry
{
  Lisp_Object key;
  Lisp_Object value;
} hentry;

struct Lisp_Hash_Table
{
  struct lcrecord_header header;
  size_t size;
  size_t count;
  size_t rehash_count;
  double rehash_size;
  double rehash_threshold;
  size_t golden_ratio;
  hash_table_hash_function_t hash_function;
  hash_table_test_function_t test_function;
  hentry *hentries;
  enum hash_table_type type; /* whether and how this hash table is weak */
  Lisp_Object next_weak;     /* Used to chain together all of the weak
                                hash tables.  Don't mark through this. */
};
typedef struct Lisp_Hash_Table Lisp_Hash_Table;

#define HENTRY_CLEAR_P(hentry) ((*(EMACS_UINT*)(&((hentry)->key))) == 0)
#define CLEAR_HENTRY(hentry)   ((*(EMACS_UINT*)(&((hentry)->key))) =  0)

#define HASH_TABLE_DEFAULT_SIZE 16
#define HASH_TABLE_DEFAULT_REHASH_SIZE 1.3
#define HASH_TABLE_MIN_SIZE 10

#define HASH_CODE(key, ht)                                                      \
  (((((ht)->hash_function ? (ht)->hash_function (key) : LISP_HASH (key))        \
     * (ht)->golden_ratio)                                                              \
    % (ht)->size))

#define KEYS_EQUAL_P(key1, key2, testfun) \
  (EQ ((key1), (key2)) || ((testfun) && (testfun) ((key1), (key2))))

#define LINEAR_PROBING_LOOP(probe, entries, size)               \
  for (;                                                        \
       !HENTRY_CLEAR_P (probe) ||                               \
         (probe == entries + size ?                             \
          (probe = entries, !HENTRY_CLEAR_P (probe)) : 0);      \
       probe++)

#ifndef ERROR_CHECK_HASH_TABLE
# ifdef ERROR_CHECK_TYPECHECK
#  define ERROR_CHECK_HASH_TABLE 1
# else
#  define ERROR_CHECK_HASH_TABLE 0
# endif
#endif

#if ERROR_CHECK_HASH_TABLE
static void
check_hash_table_invariants (Lisp_Hash_Table *ht)
{
  assert (ht->count < ht->size);
  assert (ht->count <= ht->rehash_count);
  assert (ht->rehash_count < ht->size);
  assert ((double) ht->count * ht->rehash_threshold - 1 <= (double) ht->rehash_count);
  assert (HENTRY_CLEAR_P (ht->hentries + ht->size));
}
#else
#define check_hash_table_invariants(ht)
#endif

/* We use linear probing instead of double hashing, despite its lack
   of blessing by Knuth and company, because, as a result of the
   increasing discrepancy between CPU speeds and memory speeds, cache
   behavior is becoming increasingly important, e.g:

   For a trivial loop, the penalty for non-sequential access of an array is:
    - a factor of 3-4 on Pentium Pro 200 Mhz
    - a factor of 10  on Ultrasparc  300 Mhz */

/* Return a suitable size for a hash table, with at least SIZE slots. */
static size_t
hash_table_size (size_t requested_size)
{
  /* Return some prime near, but greater than or equal to, SIZE.
     Decades from the time of writing, someone will have a system large
     enough that the list below will be too short... */
  static CONST size_t primes [] =
  {
    19, 29, 41, 59, 79, 107, 149, 197, 263, 347, 457, 599, 787, 1031,
    1361, 1777, 2333, 3037, 3967, 5167, 6719, 8737, 11369, 14783,
    19219, 24989, 32491, 42257, 54941, 71429, 92861, 120721, 156941,
    204047, 265271, 344857, 448321, 582821, 757693, 985003, 1280519,
    1664681, 2164111, 2813353, 3657361, 4754591, 6180989, 8035301,
    10445899, 13579681, 17653589, 22949669, 29834603, 38784989,
    50420551, 65546729, 85210757, 110774011, 144006217, 187208107,
    243370577, 316381771, 411296309, 534685237, 695090819, 903618083,
    1174703521, 1527114613, 1985248999, 2580823717UL, 3355070839UL
  };
  /* We've heard of binary search. */
  int low, high;
  for (low = 0, high = countof (primes) - 1; high - low > 1;)
    {
      /* Loop Invariant: size < primes [high] */
      int mid = (low + high) / 2;
      if (primes [mid] < requested_size)
        low = mid;
      else
        high = mid;
    }
  return primes [high];
}

\f
#if 0 /* I don't think these are needed any more.
         If using the general lisp_object_equal_*() functions
         causes efficiency problems, these can be resurrected. --ben */
/* equality and hash functions for Lisp strings */
int
lisp_string_equal (Lisp_Object str1, Lisp_Object str2)
{
  /* This is wrong anyway.  You can't use strcmp() on Lisp strings,
     because they can contain zero characters.  */
  return !strcmp ((char *) XSTRING_DATA (str1), (char *) XSTRING_DATA (str2));
}

static hashcode_t
lisp_string_hash (Lisp_Object obj)
{
  return hash_string (XSTRING_DATA (str), XSTRING_LENGTH (str));
}

#endif /* 0 */

static int
lisp_object_eql_equal (Lisp_Object obj1, Lisp_Object obj2)
{
  return EQ (obj1, obj2) || (FLOATP (obj1) && internal_equal (obj1, obj2, 0));
}

static hashcode_t
lisp_object_eql_hash (Lisp_Object obj)
{
  return FLOATP (obj) ? internal_hash (obj, 0) : LISP_HASH (obj);
}

static int
lisp_object_equal_equal (Lisp_Object obj1, Lisp_Object obj2)
{
  return internal_equal (obj1, obj2, 0);
}

static hashcode_t
lisp_object_equal_hash (Lisp_Object obj)
{
  return internal_hash (obj, 0);
}

\f
static Lisp_Object
mark_hash_table (Lisp_Object obj, void (*markobj) (Lisp_Object))
{
  Lisp_Hash_Table *ht = XHASH_TABLE (obj);

  /* If the hash table is weak, we don't want to mark the keys and
     values (we scan over them after everything else has been marked,
     and mark or remove them as necessary).  */
  if (ht->type == HASH_TABLE_NON_WEAK)
    {
      hentry *e, *sentinel;

      for (e = ht->hentries, sentinel = e + ht->size; e < sentinel; e++)
        if (!HENTRY_CLEAR_P (e))
          {
            markobj (e->key);
            markobj (e->value);
          }
    }
  return Qnil;
}
\f
/* Equality of hash tables.  Two hash tables are equal when they are of
   the same type and test function, they have the same number of
   elements, and for each key in the hash table, the values are `equal'.

   This is similar to Common Lisp `equalp' of hash tables, with the
   difference that CL requires the keys to be compared with the test
   function, which we don't do.  Doing that would require consing, and
   consing is a bad idea in `equal'.  Anyway, our method should provide
   the same result -- if the keys are not equal according to the test
   function, then Fgethash() in hash_table_equal_mapper() will fail.  */
static int
hash_table_equal (Lisp_Object hash_table1, Lisp_Object hash_table2, int depth)
{
  Lisp_Hash_Table *ht1 = XHASH_TABLE (hash_table1);
  Lisp_Hash_Table *ht2 = XHASH_TABLE (hash_table2);
  hentry *e, *sentinel;

  if ((ht1->test_function != ht2->test_function) ||
      (ht1->type          != ht2->type)          ||
      (ht1->count         != ht2->count))
    return 0;

  depth++;

  for (e = ht1->hentries, sentinel = e + ht1->size; e < sentinel; e++)
    if (!HENTRY_CLEAR_P (e))
      /* Look up the key in the other hash table, and compare the values. */
      {
        Lisp_Object value_in_other = Fgethash (e->key, hash_table2, Qunbound);
        if (UNBOUNDP (value_in_other) ||
            !internal_equal (e->value, value_in_other, depth))
          return 0;             /* Give up */
      }

  return 1;
}
\f
/* Printing hash tables.

   This is non-trivial, because we use a readable structure-style
   syntax for hash tables.  This means that a typical hash table will be
   readably printed in the form of:

   #s(hash-table size 2 data (key1 value1 key2 value2))

   The supported keywords are `type' (non-weak (or nil), weak,
   key-weak and value-weak), `test' (eql (or nil), eq or equal),
   `size' (a natnum or nil) and `data' (a list).

   If `print-readably' is non-nil, then a simpler syntax is used; for
   instance:

   #<hash-table size 2/13 data (key1 value1 key2 value2) 0x874d>

   The data is truncated to four pairs, and the rest is shown with
   `...'.  This printer does not cons.  */


/* Print the data of the hash table.  This maps through a Lisp
   hash table and prints key/value pairs using PRINTCHARFUN.  */
static void
print_hash_table_data (Lisp_Hash_Table *ht, Lisp_Object printcharfun)
{
  int count = 0;
  hentry *e, *sentinel;

  write_c_string (" data (", printcharfun);

  for (e = ht->hentries, sentinel = e + ht->size; e < sentinel; e++)
    if (!HENTRY_CLEAR_P (e))
      {
        if (count > 0)
          write_c_string (" ", printcharfun);
        if (!print_readably && count > 3)
          {
            write_c_string ("...", printcharfun);
            break;
          }
        print_internal (e->key, printcharfun, 1);
        write_c_string (" ", printcharfun);
        print_internal (e->value, printcharfun, 1);
        count++;
      }

  write_c_string (")", printcharfun);
}

static void
print_hash_table (Lisp_Object obj, Lisp_Object printcharfun, int escapeflag)
{
  Lisp_Hash_Table *ht = XHASH_TABLE (obj);
  char buf[128];

  write_c_string (print_readably ? "#s(hash-table" : "#<hash-table",
                  printcharfun);

  if (ht->type != HASH_TABLE_NON_WEAK)
    {
      sprintf (buf, " type %s",
               (ht->type == HASH_TABLE_WEAK       ? "weak"       :
                ht->type == HASH_TABLE_KEY_WEAK   ? "key-weak"   :
                ht->type == HASH_TABLE_VALUE_WEAK ? "value-weak" :
                "you-d-better-not-see-this"));
      write_c_string (buf, printcharfun);
    }

  /* These checks have a kludgy look to them, but they are safe.
     Due to nature of hashing, you cannot use arbitrary
     test functions anyway.  */
  if (!ht->test_function)
    write_c_string (" test eq", printcharfun);
  else if (ht->test_function == lisp_object_equal_equal)
    write_c_string (" test equal", printcharfun);
  else if (ht->test_function == lisp_object_eql_equal)
    DO_NOTHING;
  else
    abort ();

  if (ht->count || !print_readably)
    {
      if (print_readably)
        sprintf (buf, " size %lu", (unsigned long) ht->count);
      else
        sprintf (buf, " size %lu/%lu",
                 (unsigned long) ht->count,
                 (unsigned long) ht->size);
      write_c_string (buf, printcharfun);
    }

  if (ht->count)
    print_hash_table_data (ht, printcharfun);

  if (print_readably)
    write_c_string (")", printcharfun);
  else
    {
      sprintf (buf, " 0x%x>", ht->header.uid);
      write_c_string (buf, printcharfun);
    }
}

static void
finalize_hash_table (void *header, int for_disksave)
{
  if (!for_disksave)
    {
      Lisp_Hash_Table *ht = (Lisp_Hash_Table *) header;

      xfree (ht->hentries);
      ht->hentries = 0;
    }
}

DEFINE_LRECORD_IMPLEMENTATION ("hash-table", hash_table,
                               mark_hash_table, print_hash_table,
                               finalize_hash_table,
                               /* #### Implement hash_table_hash()! */
                               hash_table_equal, 0,
                               Lisp_Hash_Table);

static Lisp_Hash_Table *
xhash_table (Lisp_Object hash_table)
{
  if (!gc_in_progress)
    CHECK_HASH_TABLE (hash_table);
  check_hash_table_invariants (XHASH_TABLE (hash_table));
  return XHASH_TABLE (hash_table);
}

\f
/************************************************************************/
/*                       Creation of Hash Tables                        */
/************************************************************************/

/* Creation of hash tables, without error-checking. */
static double
hash_table_rehash_threshold (Lisp_Hash_Table *ht)
{
  return
    ht->rehash_threshold > 0.0 ? ht->rehash_threshold :
    ht->size > 4096 && !ht->test_function ? 0.7 : 0.6;
}

static void
compute_hash_table_derived_values (Lisp_Hash_Table *ht)
{
  ht->rehash_count = (size_t)
    ((double) ht->size * hash_table_rehash_threshold (ht));
  ht->golden_ratio = (size_t)
    ((double) ht->size * (.6180339887 / (double) sizeof (Lisp_Object)));
}

Lisp_Object
make_general_lisp_hash_table (size_t size,
                             enum hash_table_type type,
                             enum hash_table_test test,
                             double rehash_size,
                             double rehash_threshold)
{
  Lisp_Object hash_table;
  Lisp_Hash_Table *ht = alloc_lcrecord_type (Lisp_Hash_Table, &lrecord_hash_table);

  ht->type             = type;
  ht->rehash_size      = rehash_size;
  ht->rehash_threshold = rehash_threshold;

  switch (test)
    {
    case HASH_TABLE_EQ:
      ht->test_function = 0;
      ht->hash_function = 0;
      break;

    case HASH_TABLE_EQL:
      ht->test_function = lisp_object_eql_equal;
      ht->hash_function = lisp_object_eql_hash;
      break;

    case HASH_TABLE_EQUAL:
      ht->test_function = lisp_object_equal_equal;
      ht->hash_function = lisp_object_equal_hash;
      break;

    default:
      abort ();
    }

  if (ht->rehash_size <= 0.0)
    ht->rehash_size = HASH_TABLE_DEFAULT_REHASH_SIZE;
  if (size < HASH_TABLE_MIN_SIZE)
    size = HASH_TABLE_MIN_SIZE;
  if (rehash_threshold < 0.0)
    rehash_threshold = 0.75;
  ht->size =
    hash_table_size ((size_t) ((double) size / hash_table_rehash_threshold (ht)) + 1);
  ht->count = 0;
  compute_hash_table_derived_values (ht);

  /* We leave room for one never-occupied sentinel hentry at the end.  */
  ht->hentries = xnew_array (hentry, ht->size + 1);

  {
    hentry *e, *sentinel;
    for (e = ht->hentries, sentinel = e + ht->size; e <= sentinel; e++)
      CLEAR_HENTRY (e);
  }

  XSETHASH_TABLE (hash_table, ht);

  if (type == HASH_TABLE_NON_WEAK)
    ht->next_weak = Qunbound;
  else
    ht->next_weak = Vall_weak_hash_tables, Vall_weak_hash_tables = hash_table;

  return hash_table;
}

Lisp_Object
make_lisp_hash_table (size_t size,
                      enum hash_table_type type,
                      enum hash_table_test test)
{
  return make_general_lisp_hash_table (size, type, test,
                                       HASH_TABLE_DEFAULT_REHASH_SIZE, -1.0);
}

/* Pretty reading of hash tables.

   Here we use the existing structures mechanism (which is,
   unfortunately, pretty cumbersome) for validating and instantiating
   the hash tables.  The idea is that the side-effect of reading a
   #s(hash-table PLIST) object is creation of a hash table with desired
   properties, and that the hash table is returned.  */

/* Validation functions: each keyword provides its own validation
   function.  The errors should maybe be continuable, but it is
   unclear how this would cope with ERRB.  */
static int
hash_table_size_validate (Lisp_Object keyword, Lisp_Object value,
                         Error_behavior errb)
{
  if (NATNUMP (value))
    return 1;

  maybe_signal_error (Qwrong_type_argument, list2 (Qnatnump, value),
                      Qhash_table, errb);
  return 0;
}

static size_t
decode_hash_table_size (Lisp_Object obj)
{
  return NILP (obj) ? HASH_TABLE_DEFAULT_SIZE : XINT (obj);
}

static int
hash_table_type_validate (Lisp_Object keyword, Lisp_Object value,
                         Error_behavior errb)
{
  if (EQ (value, Qnil))         return 1;
  if (EQ (value, Qnon_weak))    return 1;
  if (EQ (value, Qweak))        return 1;
  if (EQ (value, Qkey_weak))    return 1;
  if (EQ (value, Qvalue_weak))  return 1;

  maybe_signal_simple_error ("Invalid hash table type",
                             value, Qhash_table, errb);
  return 0;
}

static enum hash_table_type
decode_hash_table_type (Lisp_Object obj)
{
  if (EQ (obj, Qnil))        return HASH_TABLE_NON_WEAK;
  if (EQ (obj, Qnon_weak))   return HASH_TABLE_NON_WEAK;
  if (EQ (obj, Qweak))       return HASH_TABLE_WEAK;
  if (EQ (obj, Qkey_weak))   return HASH_TABLE_KEY_WEAK;
  if (EQ (obj, Qvalue_weak)) return HASH_TABLE_VALUE_WEAK;

  signal_simple_error ("Invalid hash table type", obj);
  return HASH_TABLE_NON_WEAK; /* not reached */
}

static int
hash_table_test_validate (Lisp_Object keyword, Lisp_Object value,
                         Error_behavior errb)
{
  if (EQ (value, Qnil))   return 1;
  if (EQ (value, Qeq))    return 1;
  if (EQ (value, Qequal)) return 1;
  if (EQ (value, Qeql))   return 1;

  maybe_signal_simple_error ("Invalid hash table test",
                             value, Qhash_table, errb);
  return 0;
}

static enum hash_table_test
decode_hash_table_test (Lisp_Object obj)
{
  if (EQ (obj, Qnil))   return HASH_TABLE_EQL;
  if (EQ (obj, Qeq))    return HASH_TABLE_EQ;
  if (EQ (obj, Qequal)) return HASH_TABLE_EQUAL;
  if (EQ (obj, Qeql))   return HASH_TABLE_EQL;

  signal_simple_error ("Invalid hash table test", obj);
  return HASH_TABLE_EQ; /* not reached */
}

static int
hash_table_rehash_size_validate (Lisp_Object keyword, Lisp_Object value,
                                Error_behavior errb)
{
  if (!FLOATP (value))
    {
      maybe_signal_error (Qwrong_type_argument, list2 (Qfloatp, value),
                          Qhash_table, errb);
      return 0;
    }

  {
    double rehash_size = XFLOAT_DATA (value);
    if (rehash_size <= 1.0)
      {
        maybe_signal_simple_error
          ("Hash table rehash size must be greater than 1.0",
           value, Qhash_table, errb);
        return 0;
      }
  }

  return 1;
}

static double
decode_hash_table_rehash_size (Lisp_Object rehash_size)
{
  return NILP (rehash_size) ? -1.0 : XFLOAT_DATA (rehash_size);
}

static int
hash_table_rehash_threshold_validate (Lisp_Object keyword, Lisp_Object value,
                                     Error_behavior errb)
{
  if (!FLOATP (value))
    {
      maybe_signal_error (Qwrong_type_argument, list2 (Qfloatp, value),
                          Qhash_table, errb);
      return 0;
    }

  {
    double rehash_threshold = XFLOAT_DATA (value);
    if (rehash_threshold <= 0.0 || rehash_threshold >= 1.0)
      {
        maybe_signal_simple_error
          ("Hash table rehash threshold must be between 0.0 and 1.0",
           value, Qhash_table, errb);
        return 0;
      }
  }

  return 1;
}

static double
decode_hash_table_rehash_threshold (Lisp_Object rehash_threshold)
{
  return NILP (rehash_threshold) ? -1.0 : XFLOAT_DATA (rehash_threshold);
}

static int
hash_table_data_validate (Lisp_Object keyword, Lisp_Object value,
                         Error_behavior errb)
{
  int len;

  GET_EXTERNAL_LIST_LENGTH (value, len);

  if (len & 1)
    {
      maybe_signal_simple_error
        ("Hash table data must have alternating key/value pairs",
         value, Qhash_table, errb);
      return 0;
    }
  return 1;
}

/* The actual instantiation of a hash table.  This does practically no
   error checking, because it relies on the fact that the paranoid
   functions above have error-checked everything to the last details.
   If this assumption is wrong, we will get a crash immediately (with
   error-checking compiled in), and we'll know if there is a bug in
   the structure mechanism.  So there.  */
static Lisp_Object
hash_table_instantiate (Lisp_Object plist)
{
  Lisp_Object hash_table;
  Lisp_Object test             = Qnil;
  Lisp_Object type             = Qnil;
  Lisp_Object size             = Qnil;
  Lisp_Object data             = Qnil;
  Lisp_Object rehash_size      = Qnil;
  Lisp_Object rehash_threshold = Qnil;

  while (!NILP (plist))
    {
      Lisp_Object key, value;
      key   = XCAR (plist); plist = XCDR (plist);
      value = XCAR (plist); plist = XCDR (plist);

      if      (EQ (key, Qtest))             test             = value;
      else if (EQ (key, Qtype))             type             = value;
      else if (EQ (key, Qsize))             size             = value;
      else if (EQ (key, Qdata))             data             = value;
      else if (EQ (key, Qrehash_size))      rehash_size      = value;
      else if (EQ (key, Qrehash_threshold)) rehash_threshold = value;
      else
        abort ();
    }

  /* Create the hash table.  */
  hash_table = make_general_lisp_hash_table
    (decode_hash_table_size (size),
     decode_hash_table_type (type),
     decode_hash_table_test (test),
     decode_hash_table_rehash_size (rehash_size),
     decode_hash_table_rehash_threshold (rehash_threshold));

  /* I'm not sure whether this can GC, but better safe than sorry.  */
  {
    struct gcpro gcpro1;
    GCPRO1 (hash_table);

    /* And fill it with data.  */
    while (!NILP (data))
      {
        Lisp_Object key, value;
        key   = XCAR (data); data = XCDR (data);
        value = XCAR (data); data = XCDR (data);
        Fputhash (key, value, hash_table);
      }
    UNGCPRO;
  }

  return hash_table;
}

static void
structure_type_create_hash_table_structure_name (Lisp_Object structure_name)
{
  struct structure_type *st;

  st = define_structure_type (structure_name, 0, hash_table_instantiate);
  define_structure_type_keyword (st, Qsize, hash_table_size_validate);
  define_structure_type_keyword (st, Qtest, hash_table_test_validate);
  define_structure_type_keyword (st, Qtype, hash_table_type_validate);
  define_structure_type_keyword (st, Qdata, hash_table_data_validate);
  define_structure_type_keyword (st, Qrehash_size, hash_table_rehash_size_validate);
  define_structure_type_keyword (st, Qrehash_threshold, hash_table_rehash_threshold_validate);
}

/* Create a built-in Lisp structure type named `hash-table'.
   We make #s(hashtable ...) equivalent to #s(hash-table ...),
   for backward comptabibility.
   This is called from emacs.c.  */
void
structure_type_create_hash_table (void)
{
  structure_type_create_hash_table_structure_name (Qhash_table);
  structure_type_create_hash_table_structure_name (Qhashtable); /* compat */
}

\f
/************************************************************************/
/*              Definition of Lisp-visible methods                      */
/************************************************************************/

DEFUN ("hash-table-p", Fhash_table_p, 1, 1, 0, /*
Return t if OBJECT is a hash table, else nil.
*/
       (object))
{
  return HASH_TABLEP (object) ? Qt : Qnil;
}

DEFUN ("make-hash-table", Fmake_hash_table, 0, MANY, 0, /*
Return a new empty hash table object.
Use Common Lisp style keywords to specify hash table properties.
 (make-hash-table &key :size :test :type :rehash-size :rehash-threshold)

Keyword :size specifies the number of keys likely to be inserted.
This number of entries can be inserted without enlarging the hash table.

Keyword :test can be `eq', `eql' (default) or `equal'.
Comparison between keys is done using this function.
If speed is important, consider using `eq'.
When storing strings in the hash table, you will likely need to use `equal'.

Keyword :type can be `non-weak' (default), `weak', `key-weak' or `value-weak'.

A weak hash table is one whose pointers do not count as GC referents:
for any key-value pair in the hash table, if the only remaining pointer
to either the key or the value is in a weak hash table, then the pair
will be removed from the hash table, and the key and value collected.
A non-weak hash table (or any other pointer) would prevent the object
from being collected.

A key-weak hash table is similar to a fully-weak hash table except that
a key-value pair will be removed only if the key remains unmarked
outside of weak hash tables.  The pair will remain in the hash table if
the key is pointed to by something other than a weak hash table, even
if the value is not.

A value-weak hash table is similar to a fully-weak hash table except
that a key-value pair will be removed only if the value remains
unmarked outside of weak hash tables.  The pair will remain in the
hash table if the value is pointed to by something other than a weak
hash table, even if the key is not.

Keyword :rehash-size must be a float greater than 1.0, and specifies
the factor by which to increase the size of the hash table when enlarging.

Keyword :rehash-threshold must be a float between 0.0 and 1.0,
and specifies the load factor of the hash table which triggers enlarging.

*/
       (int nargs, Lisp_Object *args))
{
  int j = 0;
  Lisp_Object size             = Qnil;
  Lisp_Object type             = Qnil;
  Lisp_Object test             = Qnil;
  Lisp_Object rehash_size      = Qnil;
  Lisp_Object rehash_threshold = Qnil;

  while (j < nargs)
    {
      Lisp_Object keyword, value;

      keyword = args[j++];
      if (!KEYWORDP (keyword))
        signal_simple_error ("Invalid hash table property keyword", keyword);
      if (j == nargs)
        signal_simple_error ("Hash table property requires a value", keyword);

      value = args[j++];

      if      (EQ (keyword, Q_size))             size             = value;
      else if (EQ (keyword, Q_type))             type             = value;
      else if (EQ (keyword, Q_test))             test             = value;
      else if (EQ (keyword, Q_rehash_size))      rehash_size      = value;
      else if (EQ (keyword, Q_rehash_threshold)) rehash_threshold = value;
      else signal_simple_error ("Invalid hash table property keyword", keyword);
    }

#define VALIDATE_VAR(var) \
if (!NILP (var)) hash_table_##var##_validate (Q##var, var, ERROR_ME);

  VALIDATE_VAR (size);
  VALIDATE_VAR (type);
  VALIDATE_VAR (test);
  VALIDATE_VAR (rehash_size);
  VALIDATE_VAR (rehash_threshold);

  return make_general_lisp_hash_table
    (decode_hash_table_size (size),
     decode_hash_table_type (type),
     decode_hash_table_test (test),
     decode_hash_table_rehash_size (rehash_size),
     decode_hash_table_rehash_threshold (rehash_threshold));
}

DEFUN ("copy-hash-table", Fcopy_hash_table, 1, 1, 0, /*
Return a new hash table containing the same keys and values as HASH-TABLE.
The keys and values will not themselves be copied.
*/
       (hash_table))
{
  CONST Lisp_Hash_Table *ht_old = xhash_table (hash_table);
  Lisp_Hash_Table *ht = alloc_lcrecord_type (Lisp_Hash_Table, &lrecord_hash_table);

  copy_lcrecord (ht, ht_old);

  ht->hentries = xnew_array (hentry, ht_old->size + 1);
  memcpy (ht->hentries, ht_old->hentries, (ht_old->size + 1) * sizeof (hentry));

  XSETHASH_TABLE (hash_table, ht);

  if (! EQ (ht->next_weak, Qunbound))
    {
      ht->next_weak = Vall_weak_hash_tables;
      Vall_weak_hash_tables = hash_table;
    }

  return hash_table;
}

static void
enlarge_hash_table (Lisp_Hash_Table *ht)
{
  hentry *old_entries, *new_entries, *old_sentinel, *new_sentinel, *e;
  size_t old_size, new_size;

  old_size = ht->size;
  new_size = ht->size =
    hash_table_size ((size_t) ((double) old_size * ht->rehash_size));

  old_entries = ht->hentries;

  ht->hentries = xnew_array (hentry, new_size + 1);
  new_entries = ht->hentries;

  old_sentinel = old_entries + old_size;
  new_sentinel = new_entries + new_size;

  for (e = new_entries; e <= new_sentinel; e++)
    CLEAR_HENTRY (e);

  compute_hash_table_derived_values (ht);

  for (e = old_entries; e < old_sentinel; e++)
    if (!HENTRY_CLEAR_P (e))
      {
        hentry *probe = new_entries + HASH_CODE (e->key, ht);
        LINEAR_PROBING_LOOP (probe, new_entries, new_size)
          ;
        *probe = *e;
      }

  xfree (old_entries);
}

static hentry *
find_hentry (Lisp_Object key, CONST Lisp_Hash_Table *ht)
{
  hash_table_test_function_t test_function = ht->test_function;
  hentry *entries = ht->hentries;
  hentry *probe = entries + HASH_CODE (key, ht);

  LINEAR_PROBING_LOOP (probe, entries, ht->size)
    if (KEYS_EQUAL_P (probe->key, key, test_function))
      break;

  return probe;
}

DEFUN ("gethash", Fgethash, 2, 3, 0, /*
Find hash value for KEY in HASH-TABLE.
If there is no corresponding value, return DEFAULT (which defaults to nil).
*/
       (key, hash_table, default_))
{
  CONST Lisp_Hash_Table *ht = xhash_table (hash_table);
  hentry *e = find_hentry (key, ht);

  return HENTRY_CLEAR_P (e) ? default_ : e->value;
}

DEFUN ("puthash", Fputhash, 3, 3, 0, /*
Hash KEY to VALUE in HASH-TABLE.
*/
       (key, value, hash_table))
{
  Lisp_Hash_Table *ht = xhash_table (hash_table);
  hentry *e = find_hentry (key, ht);

  if (!HENTRY_CLEAR_P (e))
    return e->value = value;

  e->key   = key;
  e->value = value;

  if (++ht->count >= ht->rehash_count)
    enlarge_hash_table (ht);

  return value;
}

/* Remove hentry pointed at by PROBE.
   Subsequent entries are removed and reinserted.
   We don't use tombstones - too wasteful.  */
static void
remhash_1 (Lisp_Hash_Table *ht, hentry *entries, hentry *probe)
{
  size_t size = ht->size;
  CLEAR_HENTRY (probe++);
  ht->count--;

  LINEAR_PROBING_LOOP (probe, entries, size)
    {
      Lisp_Object key = probe->key;
      hentry *probe2 = entries + HASH_CODE (key, ht);
      LINEAR_PROBING_LOOP (probe2, entries, size)
        if (EQ (probe2->key, key))
          /* hentry at probe doesn't need to move. */
          goto continue_outer_loop;
      /* Move hentry from probe to new home at probe2. */
      *probe2 = *probe;
      CLEAR_HENTRY (probe);
    continue_outer_loop: continue;
    }
}

DEFUN ("remhash", Fremhash, 2, 2, 0, /*
Remove the entry for KEY from HASH-TABLE.
Do nothing if there is no entry for KEY in HASH-TABLE.
*/
       (key, hash_table))
{
  Lisp_Hash_Table *ht = xhash_table (hash_table);
  hentry *e = find_hentry (key, ht);

  if (HENTRY_CLEAR_P (e))
    return Qnil;

  remhash_1 (ht, ht->hentries, e);
  return Qt;
}

DEFUN ("clrhash", Fclrhash, 1, 1, 0, /*
Remove all entries from HASH-TABLE, leaving it empty.
*/
       (hash_table))
{
  Lisp_Hash_Table *ht = xhash_table (hash_table);
  hentry *e, *sentinel;

  for (e = ht->hentries, sentinel = e + ht->size; e < sentinel; e++)
    CLEAR_HENTRY (e);
  ht->count = 0;

  return hash_table;
}

/************************************************************************/
/*                          Accessor Functions                          */
/************************************************************************/

DEFUN ("hash-table-count", Fhash_table_count, 1, 1, 0, /*
Return the number of entries in HASH-TABLE.
*/
       (hash_table))
{
  return make_int (xhash_table (hash_table)->count);
}

DEFUN ("hash-table-size", Fhash_table_size, 1, 1, 0, /*
Return the size of HASH-TABLE.
This is the current number of slots in HASH-TABLE, whether occupied or not.
*/
       (hash_table))
{
  return make_int (xhash_table (hash_table)->size);
}

DEFUN ("hash-table-type", Fhash_table_type, 1, 1, 0, /*
Return the type of HASH-TABLE.
This can be one of `non-weak', `weak', `key-weak' or `value-weak'.
*/
       (hash_table))
{
  switch (xhash_table (hash_table)->type)
    {
    case HASH_TABLE_WEAK:       return Qweak;
    case HASH_TABLE_KEY_WEAK:   return Qkey_weak;
    case HASH_TABLE_VALUE_WEAK: return Qvalue_weak;
    default:                    return Qnon_weak;
    }
}

DEFUN ("hash-table-test", Fhash_table_test, 1, 1, 0, /*
Return the test function of HASH-TABLE.
This can be one of `eq', `eql' or `equal'.
*/
       (hash_table))
{
  hash_table_test_function_t fun = xhash_table (hash_table)->test_function;

  return (fun == lisp_object_eql_equal   ? Qeql   :
          fun == lisp_object_equal_equal ? Qequal :
          Qeq);
}

DEFUN ("hash-table-rehash-size", Fhash_table_rehash_size, 1, 1, 0, /*
Return the current rehash size of HASH-TABLE.
This is a float greater than 1.0; the factor by which HASH-TABLE
is enlarged when the rehash threshold is exceeded.
*/
       (hash_table))
{
  return make_float (xhash_table (hash_table)->rehash_size);
}

DEFUN ("hash-table-rehash-threshold", Fhash_table_rehash_threshold, 1, 1, 0, /*
Return the current rehash threshold of HASH-TABLE.
This is a float between 0.0 and 1.0; the maximum `load factor' of HASH-TABLE,
beyond which the HASH-TABLE is enlarged by rehashing.
*/
       (hash_table))
{
  return make_float (hash_table_rehash_threshold (xhash_table (hash_table)));
}

/************************************************************************/
/*                          Mapping Functions                           */
/************************************************************************/
DEFUN ("maphash", Fmaphash, 2, 2, 0, /*
Map FUNCTION over entries in HASH-TABLE, calling it with two args,
each key and value in HASH-TABLE.

FUNCTION may not modify HASH-TABLE, with the one exception that FUNCTION
may remhash or puthash the entry currently being processed by FUNCTION.
*/
       (function, hash_table))
{
  CONST Lisp_Hash_Table *ht = xhash_table (hash_table);
  CONST hentry *e, *sentinel;

  for (e = ht->hentries, sentinel = e + ht->size; e < sentinel; e++)
    if (!HENTRY_CLEAR_P (e))
      {
        Lisp_Object args[3], key;
      again:
        key = e->key;
        args[0] = function;
        args[1] = key;
        args[2] = e->value;
        Ffuncall (countof (args), args);
        /* Has FUNCTION done a remhash? */
        if (!EQ (key, e->key) && !HENTRY_CLEAR_P (e))
          goto again;
      }

  return Qnil;
}

/* Map *C* function FUNCTION over the elements of a lisp hash table. */
void
elisp_maphash (maphash_function_t function,
               Lisp_Object hash_table, void *extra_arg)
{
  CONST Lisp_Hash_Table *ht = XHASH_TABLE (hash_table);
  CONST hentry *e, *sentinel;

  for (e = ht->hentries, sentinel = e + ht->size; e < sentinel; e++)
    if (!HENTRY_CLEAR_P (e))
      {
        Lisp_Object key;
      again:
        key = e->key;
        if (function (key, e->value, extra_arg))
          return;
        /* Has FUNCTION done a remhash? */
        if (!EQ (key, e->key) && !HENTRY_CLEAR_P (e))
          goto again;
      }
}

/* Remove all elements of a lisp hash table satisfying *C* predicate PREDICATE. */
void
elisp_map_remhash (maphash_function_t predicate,
                   Lisp_Object hash_table, void *extra_arg)
{
  Lisp_Hash_Table *ht = XHASH_TABLE (hash_table);
  hentry *e, *entries, *sentinel;

  for (e = entries = ht->hentries, sentinel = e + ht->size; e < sentinel; e++)
    if (!HENTRY_CLEAR_P (e))
      {
      again:
        if (predicate (e->key, e->value, extra_arg))
          {
            remhash_1 (ht, entries, e);
            if (!HENTRY_CLEAR_P (e))
              goto again;
          }
      }
}

\f
/************************************************************************/
/*                 garbage collecting weak hash tables                  */
/************************************************************************/

/* Complete the marking for semi-weak hash tables. */
int
finish_marking_weak_hash_tables (int (*obj_marked_p) (Lisp_Object),
                                void (*markobj) (Lisp_Object))
{
  Lisp_Object hash_table;
  int did_mark = 0;

  for (hash_table = Vall_weak_hash_tables;
       !GC_NILP (hash_table);
       hash_table = XHASH_TABLE (hash_table)->next_weak)
    {
      CONST Lisp_Hash_Table *ht = XHASH_TABLE (hash_table);
      CONST hentry *e = ht->hentries;
      CONST hentry *sentinel = e + ht->size;

      if (! obj_marked_p (hash_table))
        /* The hash table is probably garbage.  Ignore it. */
        continue;

      /* Now, scan over all the pairs.  For all pairs that are
         half-marked, we may need to mark the other half if we're
         keeping this pair. */
#define MARK_OBJ(obj) \
do { if (!obj_marked_p (obj)) markobj (obj), did_mark = 1; } while (0)

      switch (ht->type)
        {
        case HASH_TABLE_KEY_WEAK:
          for (; e < sentinel; e++)
            if (!HENTRY_CLEAR_P (e))
              if (obj_marked_p (e->key))
                MARK_OBJ (e->value);
          break;

        case HASH_TABLE_VALUE_WEAK:
          for (; e < sentinel; e++)
            if (!HENTRY_CLEAR_P (e))
              if (obj_marked_p (e->value))
                MARK_OBJ (e->key);
          break;

        case HASH_TABLE_KEY_CAR_WEAK:
          for (; e < sentinel; e++)
            if (!HENTRY_CLEAR_P (e))
              if (!CONSP (e->key) || obj_marked_p (XCAR (e->key)))
                {
                  MARK_OBJ (e->key);
                  MARK_OBJ (e->value);
                }
          break;

        case HASH_TABLE_VALUE_CAR_WEAK:
          for (; e < sentinel; e++)
            if (!HENTRY_CLEAR_P (e))
              if (!CONSP (e->value) || obj_marked_p (XCAR (e->value)))
                {
                  MARK_OBJ (e->key);
                  MARK_OBJ (e->value);
                }
          break;

        default:
          break;
        }
    }

  return did_mark;
}

void
prune_weak_hash_tables (int (*obj_marked_p) (Lisp_Object))
{
  Lisp_Object hash_table, prev = Qnil;
  for (hash_table = Vall_weak_hash_tables;
       !GC_NILP (hash_table);
       hash_table = XHASH_TABLE (hash_table)->next_weak)
    {
      if (! obj_marked_p (hash_table))
        {
          /* This hash table itself is garbage.  Remove it from the list. */
          if (GC_NILP (prev))
            Vall_weak_hash_tables = XHASH_TABLE (hash_table)->next_weak;
          else
            XHASH_TABLE (prev)->next_weak = XHASH_TABLE (hash_table)->next_weak;
        }
      else
        {
          /* Now, scan over all the pairs.  Remove all of the pairs
             in which the key or value, or both, is unmarked
             (depending on the type of weak hash table). */
          Lisp_Hash_Table *ht = XHASH_TABLE (hash_table);
          hentry *entries = ht->hentries;
          hentry *sentinel = entries + ht->size;
          hentry *e;

          for (e = entries; e < sentinel; e++)
            if (!HENTRY_CLEAR_P (e))
              {
              again:
                if (!obj_marked_p (e->key) || !obj_marked_p (e->value))
                  {
                    remhash_1 (ht, entries, e);
                    if (!HENTRY_CLEAR_P (e))
                      goto again;
                  }
              }

          prev = hash_table;
        }
    }
}

/* Return a hash value for an array of Lisp_Objects of size SIZE. */

hashcode_t
internal_array_hash (Lisp_Object *arr, int size, int depth)
{
  int i;
  unsigned long hash = 0;

  if (size <= 5)
    {
      for (i = 0; i < size; i++)
        hash = HASH2 (hash, internal_hash (arr[i], depth + 1));
      return hash;
    }

  /* just pick five elements scattered throughout the array.
     A slightly better approach would be to offset by some
     noise factor from the points chosen below. */
  for (i = 0; i < 5; i++)
    hash = HASH2 (hash, internal_hash (arr[i*size/5], depth + 1));

  return hash;
}

/* Return a hash value for a Lisp_Object.  This is for use when hashing
   objects with the comparison being `equal' (for `eq', you can just
   use the Lisp_Object itself as the hash value).  You need to make a
   tradeoff between the speed of the hash function and how good the
   hashing is.  In particular, the hash function needs to be FAST,
   so you can't just traipse down the whole tree hashing everything
   together.  Most of the time, objects will differ in the first
   few elements you hash.  Thus, we only go to a short depth (5)
   and only hash at most 5 elements out of a vector.  Theoretically
   we could still take 5^5 time (a big big number) to compute a
   hash, but practically this won't ever happen. */

hashcode_t
internal_hash (Lisp_Object obj, int depth)
{
  if (depth > 5)
    return 0;
  if (CONSP (obj))
    {
      /* no point in worrying about tail recursion, since we're not
         going very deep */
      return HASH2 (internal_hash (XCAR (obj), depth + 1),
                    internal_hash (XCDR (obj), depth + 1));
    }
  if (STRINGP (obj))
    {
      return hash_string (XSTRING_DATA (obj), XSTRING_LENGTH (obj));
    }
  if (VECTORP (obj))
    {
      return HASH2 (XVECTOR_LENGTH (obj),
                    internal_array_hash (XVECTOR_DATA (obj),
                                         XVECTOR_LENGTH (obj),
                                         depth + 1));
    }
  if (LRECORDP (obj))
    {
      CONST struct lrecord_implementation
        *imp = XRECORD_LHEADER_IMPLEMENTATION (obj);
      if (imp->hash)
        return imp->hash (obj, depth);
    }

  return LISP_HASH (obj);
}

#if 0
xxDEFUN ("internal-hash-value", Finternal_hash_value, 1, 1, 0, /*
Hash value of OBJECT.  For debugging.
The value is returned as (HIGH . LOW).
*/
       (object))
{
  /* This function is pretty 32bit-centric. */
  unsigned long hash = internal_hash (object, 0);
  return Fcons (hash >> 16, hash & 0xffff);
}
#endif

\f
/************************************************************************/
/*                            initialization                            */
/************************************************************************/

void
syms_of_elhash (void)
{
  DEFSUBR (Fhash_table_p);
  DEFSUBR (Fmake_hash_table);
  DEFSUBR (Fcopy_hash_table);
  DEFSUBR (Fgethash);
  DEFSUBR (Fremhash);
  DEFSUBR (Fputhash);
  DEFSUBR (Fclrhash);
  DEFSUBR (Fmaphash);
  DEFSUBR (Fhash_table_count);
  DEFSUBR (Fhash_table_size);
  DEFSUBR (Fhash_table_rehash_size);
  DEFSUBR (Fhash_table_rehash_threshold);
  DEFSUBR (Fhash_table_type);
  DEFSUBR (Fhash_table_test);
#if 0
  DEFSUBR (Finternal_hash_value);
#endif

  defsymbol (&Qhash_tablep, "hash-table-p");
  defsymbol (&Qhash_table, "hash-table");
  defsymbol (&Qhashtable, "hashtable");
  defsymbol (&Qweak, "weak");
  defsymbol (&Qkey_weak, "key-weak");
  defsymbol (&Qvalue_weak, "value-weak");
  defsymbol (&Qnon_weak, "non-weak");
  defsymbol (&Qrehash_size, "rehash-size");
  defsymbol (&Qrehash_threshold, "rehash-threshold");

  defkeyword (&Q_size, ":size");
  defkeyword (&Q_test, ":test");
  defkeyword (&Q_type, ":type");
  defkeyword (&Q_rehash_size, ":rehash-size");
  defkeyword (&Q_rehash_threshold, ":rehash-threshold");
}

void
vars_of_elhash (void)
{
  /* This must NOT be staticpro'd */
  Vall_weak_hash_tables = Qnil;
}