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/* Set operations on pointers

   Copyright (C) 2004 Free Software Foundation, Inc.

This file is part of GCC.

GCC 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.

GCC 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 GCC; see the file COPYING.  If not, write to

the Free Software Foundation, 51 Franklin Street, Fifth Floor,

Boston, MA 02110-1301, USA.  */

#include "config.h"

#include "system.h"

#include "pointer-set.h"

/* A pointer sets is represented as a simple open-addressing hash

   table.  Simplifications: The hash code is based on the value of the

   pointer, not what it points to.  The number of buckets is always a

   power of 2.  Null pointers are a reserved value.  Deletion is not

   supported.  There is no mechanism for user control of hash

   function, equality comparison, initial size, or resizing policy.

*/

struct pointer_set_t

{

  size_t log_slots;

  size_t n_slots;               /* n_slots = 2^log_slots */

  size_t n_elements;

  void **slots;

};

/* Use the multiplicative method, as described in Knuth 6.4, to obtain

   a hash code for P in the range [0, MAX).  MAX == 2^LOGMAX.

   Summary of this method: Multiply p by some number A that's

   relatively prime to 2^sizeof(size_t).  The result is two words.

   Discard the most significant word, and return the most significant

   N bits of the least significant word.  As suggested by Knuth, our

   choice for A is the integer part of (ULONG_MAX + 1.0) / phi, where phi

   is the golden ratio.

   We don't need to do anything special for full-width multiplication

   because we're only interested in the least significant word of the

   product, and unsigned arithmetic in C is modulo the word size.  */

static inline size_t

hash1 (const void *p, unsigned long max, unsigned long logmax)

{

#if HOST_BITS_PER_LONG == 32

  const unsigned long A = 0x9e3779b9u;

#elif HOST_BITS_PER_LONG == 64

  const unsigned long A = 0x9e3779b97f4a7c16ul;

#else

  const unsigned long A

    = (ULONG_MAX + 1.0L) * 0.6180339887498948482045868343656381177203L;

#endif

  const unsigned long shift = HOST_BITS_PER_LONG - logmax;

  return ((A * (unsigned long) p) >> shift) & (max - 1);

}

/* Allocate an empty pointer set.  */

struct pointer_set_t *

pointer_set_create (void)

{

  struct pointer_set_t *result = XNEW (struct pointer_set_t);

  result->n_elements = 0;

  result->log_slots = 8;

  result->n_slots = (size_t) 1 << result->log_slots;

  result->slots = XCNEWVEC (void *, result->n_slots);

  return result;

}

/* Reclaims all memory associated with PSET.  */

void pointer_set_destroy (struct pointer_set_t *pset)

{

  XDELETEVEC (pset->slots);

  XDELETE (pset);

}

/* Returns nonzero if PSET contains P.  P must be nonnull.

   Collisions are resolved by linear probing.  */

int

pointer_set_contains (struct pointer_set_t *pset, void *p)

{

  size_t n = hash1 (p, pset->n_slots, pset->log_slots);

  while (true)

    {

      if (pset->slots[n] == p)

       return 1;

      else if (pset->slots[n] == 0)

       return 0;

      else

       {

         ++n;

         if (n == pset->n_slots)

           n = 0;

       }

    }

}

/* Subroutine of pointer_set_insert.  Inserts P into an empty

   element of SLOTS, an array of length N_SLOTS.  Returns nonzero

   if P was already present in N_SLOTS.  */

static int

insert_aux (void *p, void **slots, size_t n_slots, size_t log_slots)

{

  size_t n = hash1 (p, n_slots, log_slots);

  while (true)

    {

      if (slots[n] == p)

        return 1;

      else if (slots[n] == 0)

        {

          slots[n] = p;

          return 0;

        }

      else

        {

          ++n;

          if (n == n_slots)

            n = 0;

        }

    }

}

/* Inserts P into PSET if it wasn't already there.  Returns nonzero

   if it was already there. P must be nonnull.  */

int

pointer_set_insert (struct pointer_set_t *pset, void *p)

{

  if (insert_aux (p, pset->slots, pset->n_slots, pset->log_slots))

    return 1;

  /* We've inserted a new element.  Expand the table if necessary to keep

     the load factor small.  */

  ++pset->n_elements;

  if (pset->n_elements > pset->n_slots / 4)

    {

      size_t new_log_slots = pset->log_slots + 1;

      size_t new_n_slots = pset->n_slots * 2;

      void **new_slots = XCNEWVEC (void *, new_n_slots);

      size_t i;

      for (i = 0; i < pset->n_slots; ++i)

        {

          if (pset->slots[i])

            insert_aux (pset->slots[i], new_slots, new_n_slots, new_log_slots);

        }

      XDELETEVEC (pset->slots);

      pset->n_slots = new_n_slots;

      pset->log_slots = new_log_slots;

      pset->slots = new_slots;

    }

  return 0;

}