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/* Set operations on pointers
Copyright (C) 2004,2006,2007,2009 Free Software Foundation, Inc.
This file is part of GNU Smalltalk.
GNU Smalltalk 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.
GNU Smalltalk 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 GNU Smalltalk; 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 <stdlib.h>
#include <limits.h>
#include "pointer-set.h"
/* A pointer set 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 (yet). 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;
const 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 SIZEOF_LONG == 4
const unsigned long A = 0x9e3779b9u;
#elif SIZEOF_LONG == 8
const unsigned long A = 0x9e3779b97f4a7c16ul;
#else
const unsigned long A
= (ULONG_MAX + 1.0L) * 0.6180339887498948482045868343656381177203L;
#endif
const unsigned long shift = (SIZEOF_LONG * 8) - 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 = malloc (sizeof (struct pointer_set_t));
result->n_elements = 0;
result->log_slots = 8;
result->n_slots = (size_t) 1 << result->log_slots;
result->slots = calloc (sizeof (const void *), result->n_slots);
return result;
}
/* Reclaims all memory associated with PSET. */
void
pointer_set_destroy (struct pointer_set_t *pset)
{
free (pset->slots);
free (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);
for (;;)
{
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. Return the insertion slot for P into
an empty element of SLOTS, an array of length N_SLOTS. */
static inline size_t
insert_aux (const void *p, const void **slots, size_t n_slots, size_t log_slots)
{
size_t n = hash1 (p, n_slots, log_slots);
for (;;)
{
if (slots[n] == p || slots[n] == 0)
return n;
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)
{
size_t n;
/* For simplicity, expand the set even if P is already there. This can be
superfluous but can happen at most once. */
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;
const void **new_slots = calloc (sizeof (const void *), new_n_slots);
size_t i;
for (i = 0; i < pset->n_slots; ++i)
{
const void *value = pset->slots[i];
n = insert_aux (value, new_slots, new_n_slots, new_log_slots);
new_slots[n] = value;
}
free (pset->slots);
pset->n_slots = new_n_slots;
pset->log_slots = new_log_slots;
pset->slots = new_slots;
}
n = insert_aux (p, pset->slots, pset->n_slots, pset->log_slots);
if (pset->slots[n])
return 1;
pset->slots[n] = p;
++pset->n_elements;
return 0;
}
/* Pass each pointer in PSET to the function in FN, together with the fixed
parameter DATA. If FN returns false, the iteration stops. */
void pointer_set_traverse (struct pointer_set_t *pset,
char (*fn) (const void *, void *), void *data)
{
size_t i;
for (i = 0; i < pset->n_slots; ++i)
if (pset->slots[i] && !fn (pset->slots[i], data))
break;
}
/* A pointer map is represented the same way as a pointer_set, so
the hash code is based on the address of the key, rather than
its contents. Null keys are a reserved value. Deletion is not
supported (yet). There is no mechanism for user control of hash
function, equality comparison, initial size, or resizing policy. */
struct pointer_map_t
{
size_t log_slots;
size_t n_slots; /* n_slots = 2^log_slots */
size_t n_elements;
const void **keys;
void **values;
};
/* Allocate an empty pointer map. */
struct pointer_map_t *
pointer_map_create (void)
{
struct pointer_map_t *result = malloc (sizeof (struct pointer_map_t));
result->n_elements = 0;
result->log_slots = 8;
result->n_slots = (size_t) 1 << result->log_slots;
result->keys = calloc (sizeof (const void *), result->n_slots);
result->values = calloc (sizeof (void *), result->n_slots);
return result;
}
/* Reclaims all memory associated with PMAP. */
void pointer_map_destroy (struct pointer_map_t *pmap)
{
free (pmap->keys);
free (pmap->values);
free (pmap);
}
/* Returns a pointer to the value to which P maps, if PMAP contains P. P
must be nonnull. Return NULL if PMAP does not contain P.
Collisions are resolved by linear probing. */
void **
pointer_map_contains (struct pointer_map_t *pmap, void *p)
{
size_t n = hash1 (p, pmap->n_slots, pmap->log_slots);
for (;;)
{
if (pmap->keys[n] == p)
return &pmap->values[n];
else if (pmap->keys[n] == 0)
return NULL;
else
{
++n;
if (n == pmap->n_slots)
n = 0;
}
}
}
/* Inserts P into PMAP if it wasn't already there. Returns a pointer
to the value. P must be nonnull. */
void **
pointer_map_insert (struct pointer_map_t *pmap, void *p)
{
size_t n;
/* For simplicity, expand the map even if P is already there. This can be
superfluous but can happen at most once. */
if (pmap->n_elements > pmap->n_slots / 4)
{
size_t new_log_slots = pmap->log_slots + 1;
size_t new_n_slots = pmap->n_slots * 2;
const void **new_keys = calloc (sizeof (const void *), new_n_slots);
void **new_values = calloc (sizeof (void *), new_n_slots);
size_t i;
for (i = 0; i < pmap->n_slots; ++i)
if (pmap->keys[i])
{
const void *key = pmap->keys[i];
n = insert_aux (key, new_keys, new_n_slots, new_log_slots);
new_keys[n] = key;
new_values[n] = pmap->values[i];
}
free (pmap->keys);
free (pmap->values);
pmap->n_slots = new_n_slots;
pmap->log_slots = new_log_slots;
pmap->keys = new_keys;
pmap->values = new_values;
}
n = insert_aux (p, pmap->keys, pmap->n_slots, pmap->log_slots);
if (!pmap->keys[n])
{
++pmap->n_elements;
pmap->keys[n] = p;
}
return &pmap->values[n];
}
/* Pass each pointer in PMAP to the function in FN, together with the pointer
to the value and the fixed parameter DATA. If FN returns false, the
iteration stops. */
void pointer_map_traverse (struct pointer_map_t *pmap,
char (*fn) (const void *, void **, void *), void *data)
{
size_t i;
for (i = 0; i < pmap->n_slots; ++i)
if (pmap->keys[i] && !fn (pmap->keys[i], &pmap->values[i], data))
break;
}