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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;
}
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