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rm_/lib/hash.c
aixiao 94bccd8e8d based on coreutils-8.32
2020-09-02 16:47:03 +08:00

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/* hash - hashing table processing.
Copyright (C) 1998-2004, 2006-2007, 2009-2020 Free Software Foundation, Inc.
Written by Jim Meyering, 1992.
This program 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.
This program 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 this program. If not, see <https://www.gnu.org/licenses/>. */
/* A generic hash table package. */
/* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead
of malloc. If you change USE_OBSTACK, you have to recompile! */
#include <config.h>
#include "hash.h"
#include "bitrotate.h"
#include "xalloc-oversized.h"
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#if USE_OBSTACK
# include "obstack.h"
# ifndef obstack_chunk_alloc
# define obstack_chunk_alloc malloc
# endif
# ifndef obstack_chunk_free
# define obstack_chunk_free free
# endif
#endif
struct hash_entry
{
void *data;
struct hash_entry *next;
};
struct hash_table
{
/* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1,
for a possibility of N_BUCKETS. Among those, N_BUCKETS_USED buckets
are not empty, there are N_ENTRIES active entries in the table. */
struct hash_entry *bucket;
struct hash_entry const *bucket_limit;
size_t n_buckets;
size_t n_buckets_used;
size_t n_entries;
/* Tuning arguments, kept in a physically separate structure. */
const Hash_tuning *tuning;
/* Three functions are given to 'hash_initialize', see the documentation
block for this function. In a word, HASHER randomizes a user entry
into a number up from 0 up to some maximum minus 1; COMPARATOR returns
true if two user entries compare equally; and DATA_FREER is the cleanup
function for a user entry. */
Hash_hasher hasher;
Hash_comparator comparator;
Hash_data_freer data_freer;
/* A linked list of freed struct hash_entry structs. */
struct hash_entry *free_entry_list;
#if USE_OBSTACK
/* Whenever obstacks are used, it is possible to allocate all overflowed
entries into a single stack, so they all can be freed in a single
operation. It is not clear if the speedup is worth the trouble. */
struct obstack entry_stack;
#endif
};
/* A hash table contains many internal entries, each holding a pointer to
some user-provided data (also called a user entry). An entry indistinctly
refers to both the internal entry and its associated user entry. A user
entry contents may be hashed by a randomization function (the hashing
function, or just "hasher" for short) into a number (or "slot") between 0
and the current table size. At each slot position in the hash table,
starts a linked chain of entries for which the user data all hash to this
slot. A bucket is the collection of all entries hashing to the same slot.
A good "hasher" function will distribute entries rather evenly in buckets.
In the ideal case, the length of each bucket is roughly the number of
entries divided by the table size. Finding the slot for a data is usually
done in constant time by the "hasher", and the later finding of a precise
entry is linear in time with the size of the bucket. Consequently, a
larger hash table size (that is, a larger number of buckets) is prone to
yielding shorter chains, *given* the "hasher" function behaves properly.
Long buckets slow down the lookup algorithm. One might use big hash table
sizes in hope to reduce the average length of buckets, but this might
become inordinate, as unused slots in the hash table take some space. The
best bet is to make sure you are using a good "hasher" function (beware
that those are not that easy to write! :-), and to use a table size
larger than the actual number of entries. */
/* If an insertion makes the ratio of nonempty buckets to table size larger
than the growth threshold (a number between 0.0 and 1.0), then increase
the table size by multiplying by the growth factor (a number greater than
1.0). The growth threshold defaults to 0.8, and the growth factor
defaults to 1.414, meaning that the table will have doubled its size
every second time 80% of the buckets get used. */
#define DEFAULT_GROWTH_THRESHOLD 0.8f
#define DEFAULT_GROWTH_FACTOR 1.414f
/* If a deletion empties a bucket and causes the ratio of used buckets to
table size to become smaller than the shrink threshold (a number between
0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a
number greater than the shrink threshold but smaller than 1.0). The shrink
threshold and factor default to 0.0 and 1.0, meaning that the table never
shrinks. */
#define DEFAULT_SHRINK_THRESHOLD 0.0f
#define DEFAULT_SHRINK_FACTOR 1.0f
/* Use this to initialize or reset a TUNING structure to
some sensible values. */
static const Hash_tuning default_tuning =
{
DEFAULT_SHRINK_THRESHOLD,
DEFAULT_SHRINK_FACTOR,
DEFAULT_GROWTH_THRESHOLD,
DEFAULT_GROWTH_FACTOR,
false
};
/* Information and lookup. */
/* The following few functions provide information about the overall hash
table organization: the number of entries, number of buckets and maximum
length of buckets. */
/* Return the number of buckets in the hash table. The table size, the total
number of buckets (used plus unused), or the maximum number of slots, are
the same quantity. */
size_t
hash_get_n_buckets (const Hash_table *table)
{
return table->n_buckets;
}
/* Return the number of slots in use (non-empty buckets). */
size_t
hash_get_n_buckets_used (const Hash_table *table)
{
return table->n_buckets_used;
}
/* Return the number of active entries. */
size_t
hash_get_n_entries (const Hash_table *table)
{
return table->n_entries;
}
/* Return the length of the longest chain (bucket). */
size_t
hash_get_max_bucket_length (const Hash_table *table)
{
struct hash_entry const *bucket;
size_t max_bucket_length = 0;
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
if (bucket->data)
{
struct hash_entry const *cursor = bucket;
size_t bucket_length = 1;
while (cursor = cursor->next, cursor)
bucket_length++;
if (bucket_length > max_bucket_length)
max_bucket_length = bucket_length;
}
}
return max_bucket_length;
}
/* Do a mild validation of a hash table, by traversing it and checking two
statistics. */
bool
hash_table_ok (const Hash_table *table)
{
struct hash_entry const *bucket;
size_t n_buckets_used = 0;
size_t n_entries = 0;
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
if (bucket->data)
{
struct hash_entry const *cursor = bucket;
/* Count bucket head. */
n_buckets_used++;
n_entries++;
/* Count bucket overflow. */
while (cursor = cursor->next, cursor)
n_entries++;
}
}
if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries)
return true;
return false;
}
void
hash_print_statistics (const Hash_table *table, FILE *stream)
{
size_t n_entries = hash_get_n_entries (table);
size_t n_buckets = hash_get_n_buckets (table);
size_t n_buckets_used = hash_get_n_buckets_used (table);
size_t max_bucket_length = hash_get_max_bucket_length (table);
fprintf (stream, "# entries: %lu\n", (unsigned long int) n_entries);
fprintf (stream, "# buckets: %lu\n", (unsigned long int) n_buckets);
fprintf (stream, "# buckets used: %lu (%.2f%%)\n",
(unsigned long int) n_buckets_used,
(100.0 * n_buckets_used) / n_buckets);
fprintf (stream, "max bucket length: %lu\n",
(unsigned long int) max_bucket_length);
}
/* Hash KEY and return a pointer to the selected bucket.
If TABLE->hasher misbehaves, abort. */
static struct hash_entry *
safe_hasher (const Hash_table *table, const void *key)
{
size_t n = table->hasher (key, table->n_buckets);
if (! (n < table->n_buckets))
abort ();
return table->bucket + n;
}
/* If ENTRY matches an entry already in the hash table, return the
entry from the table. Otherwise, return NULL. */
void *
hash_lookup (const Hash_table *table, const void *entry)
{
struct hash_entry const *bucket = safe_hasher (table, entry);
struct hash_entry const *cursor;
if (bucket->data == NULL)
return NULL;
for (cursor = bucket; cursor; cursor = cursor->next)
if (entry == cursor->data || table->comparator (entry, cursor->data))
return cursor->data;
return NULL;
}
/* Walking. */
/* The functions in this page traverse the hash table and process the
contained entries. For the traversal to work properly, the hash table
should not be resized nor modified while any particular entry is being
processed. In particular, entries should not be added, and an entry
may be removed only if there is no shrink threshold and the entry being
removed has already been passed to hash_get_next. */
/* Return the first data in the table, or NULL if the table is empty. */
void *
hash_get_first (const Hash_table *table)
{
struct hash_entry const *bucket;
if (table->n_entries == 0)
return NULL;
for (bucket = table->bucket; ; bucket++)
if (! (bucket < table->bucket_limit))
abort ();
else if (bucket->data)
return bucket->data;
}
/* Return the user data for the entry following ENTRY, where ENTRY has been
returned by a previous call to either 'hash_get_first' or 'hash_get_next'.
Return NULL if there are no more entries. */
void *
hash_get_next (const Hash_table *table, const void *entry)
{
struct hash_entry const *bucket = safe_hasher (table, entry);
struct hash_entry const *cursor;
/* Find next entry in the same bucket. */
cursor = bucket;
do
{
if (cursor->data == entry && cursor->next)
return cursor->next->data;
cursor = cursor->next;
}
while (cursor != NULL);
/* Find first entry in any subsequent bucket. */
while (++bucket < table->bucket_limit)
if (bucket->data)
return bucket->data;
/* None found. */
return NULL;
}
/* Fill BUFFER with pointers to active user entries in the hash table, then
return the number of pointers copied. Do not copy more than BUFFER_SIZE
pointers. */
size_t
hash_get_entries (const Hash_table *table, void **buffer,
size_t buffer_size)
{
size_t counter = 0;
struct hash_entry const *bucket;
struct hash_entry const *cursor;
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
if (bucket->data)
{
for (cursor = bucket; cursor; cursor = cursor->next)
{
if (counter >= buffer_size)
return counter;
buffer[counter++] = cursor->data;
}
}
}
return counter;
}
/* Call a PROCESSOR function for each entry of a hash table, and return the
number of entries for which the processor function returned success. A
pointer to some PROCESSOR_DATA which will be made available to each call to
the processor function. The PROCESSOR accepts two arguments: the first is
the user entry being walked into, the second is the value of PROCESSOR_DATA
as received. The walking continue for as long as the PROCESSOR function
returns nonzero. When it returns zero, the walking is interrupted. */
size_t
hash_do_for_each (const Hash_table *table, Hash_processor processor,
void *processor_data)
{
size_t counter = 0;
struct hash_entry const *bucket;
struct hash_entry const *cursor;
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
if (bucket->data)
{
for (cursor = bucket; cursor; cursor = cursor->next)
{
if (! processor (cursor->data, processor_data))
return counter;
counter++;
}
}
}
return counter;
}
/* Allocation and clean-up. */
/* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
This is a convenience routine for constructing other hashing functions. */
#if USE_DIFF_HASH
/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
Software--practice & experience 20, 2 (Feb 1990), 209-224. Good hash
algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
may not be good for your application." */
size_t
hash_string (const char *string, size_t n_buckets)
{
# define HASH_ONE_CHAR(Value, Byte) \
((Byte) + rotl_sz (Value, 7))
size_t value = 0;
unsigned char ch;
for (; (ch = *string); string++)
value = HASH_ONE_CHAR (value, ch);
return value % n_buckets;
# undef HASH_ONE_CHAR
}
#else /* not USE_DIFF_HASH */
/* This one comes from 'recode', and performs a bit better than the above as
per a few experiments. It is inspired from a hashing routine found in the
very old Cyber 'snoop', itself written in typical Greg Mansfield style.
(By the way, what happened to this excellent man? Is he still alive?) */
size_t
hash_string (const char *string, size_t n_buckets)
{
size_t value = 0;
unsigned char ch;
for (; (ch = *string); string++)
value = (value * 31 + ch) % n_buckets;
return value;
}
#endif /* not USE_DIFF_HASH */
/* Return true if CANDIDATE is a prime number. CANDIDATE should be an odd
number at least equal to 11. */
static bool _GL_ATTRIBUTE_CONST
is_prime (size_t candidate)
{
size_t divisor = 3;
size_t square = divisor * divisor;
while (square < candidate && (candidate % divisor))
{
divisor++;
square += 4 * divisor;
divisor++;
}
return (candidate % divisor ? true : false);
}
/* Round a given CANDIDATE number up to the nearest prime, and return that
prime. Primes lower than 10 are merely skipped. */
static size_t _GL_ATTRIBUTE_CONST
next_prime (size_t candidate)
{
/* Skip small primes. */
if (candidate < 10)
candidate = 10;
/* Make it definitely odd. */
candidate |= 1;
while (SIZE_MAX != candidate && !is_prime (candidate))
candidate += 2;
return candidate;
}
void
hash_reset_tuning (Hash_tuning *tuning)
{
*tuning = default_tuning;
}
/* If the user passes a NULL hasher, we hash the raw pointer. */
static size_t
raw_hasher (const void *data, size_t n)
{
/* When hashing unique pointers, it is often the case that they were
generated by malloc and thus have the property that the low-order
bits are 0. As this tends to give poorer performance with small
tables, we rotate the pointer value before performing division,
in an attempt to improve hash quality. */
size_t val = rotr_sz ((size_t) data, 3);
return val % n;
}
/* If the user passes a NULL comparator, we use pointer comparison. */
static bool
raw_comparator (const void *a, const void *b)
{
return a == b;
}
/* For the given hash TABLE, check the user supplied tuning structure for
reasonable values, and return true if there is no gross error with it.
Otherwise, definitively reset the TUNING field to some acceptable default
in the hash table (that is, the user loses the right of further modifying
tuning arguments), and return false. */
static bool
check_tuning (Hash_table *table)
{
const Hash_tuning *tuning = table->tuning;
float epsilon;
if (tuning == &default_tuning)
return true;
/* Be a bit stricter than mathematics would require, so that
rounding errors in size calculations do not cause allocations to
fail to grow or shrink as they should. The smallest allocation
is 11 (due to next_prime's algorithm), so an epsilon of 0.1
should be good enough. */
epsilon = 0.1f;
if (epsilon < tuning->growth_threshold
&& tuning->growth_threshold < 1 - epsilon
&& 1 + epsilon < tuning->growth_factor
&& 0 <= tuning->shrink_threshold
&& tuning->shrink_threshold + epsilon < tuning->shrink_factor
&& tuning->shrink_factor <= 1
&& tuning->shrink_threshold + epsilon < tuning->growth_threshold)
return true;
table->tuning = &default_tuning;
return false;
}
/* Compute the size of the bucket array for the given CANDIDATE and
TUNING, or return 0 if there is no possible way to allocate that
many entries. */
static size_t _GL_ATTRIBUTE_PURE
compute_bucket_size (size_t candidate, const Hash_tuning *tuning)
{
if (!tuning->is_n_buckets)
{
float new_candidate = candidate / tuning->growth_threshold;
if (SIZE_MAX <= new_candidate)
return 0;
candidate = new_candidate;
}
candidate = next_prime (candidate);
if (xalloc_oversized (candidate, sizeof (struct hash_entry *)))
return 0;
return candidate;
}
/* Allocate and return a new hash table, or NULL upon failure. The initial
number of buckets is automatically selected so as to _guarantee_ that you
may insert at least CANDIDATE different user entries before any growth of
the hash table size occurs. So, if have a reasonably tight a-priori upper
bound on the number of entries you intend to insert in the hash table, you
may save some table memory and insertion time, by specifying it here. If
the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
argument has its meaning changed to the wanted number of buckets.
TUNING points to a structure of user-supplied values, in case some fine
tuning is wanted over the default behavior of the hasher. If TUNING is
NULL, the default tuning parameters are used instead. If TUNING is
provided but the values requested are out of bounds or might cause
rounding errors, return NULL.
The user-supplied HASHER function, when not NULL, accepts two
arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a
slot number for that entry which should be in the range 0..TABLE_SIZE-1.
This slot number is then returned.
The user-supplied COMPARATOR function, when not NULL, accepts two
arguments pointing to user data, it then returns true for a pair of entries
that compare equal, or false otherwise. This function is internally called
on entries which are already known to hash to the same bucket index,
but which are distinct pointers.
The user-supplied DATA_FREER function, when not NULL, may be later called
with the user data as an argument, just before the entry containing the
data gets freed. This happens from within 'hash_free' or 'hash_clear'.
You should specify this function only if you want these functions to free
all of your 'data' data. This is typically the case when your data is
simply an auxiliary struct that you have malloc'd to aggregate several
values. */
Hash_table *
hash_initialize (size_t candidate, const Hash_tuning *tuning,
Hash_hasher hasher, Hash_comparator comparator,
Hash_data_freer data_freer)
{
Hash_table *table;
if (hasher == NULL)
hasher = raw_hasher;
if (comparator == NULL)
comparator = raw_comparator;
table = malloc (sizeof *table);
if (table == NULL)
return NULL;
if (!tuning)
tuning = &default_tuning;
table->tuning = tuning;
if (!check_tuning (table))
{
/* Fail if the tuning options are invalid. This is the only occasion
when the user gets some feedback about it. Once the table is created,
if the user provides invalid tuning options, we silently revert to
using the defaults, and ignore further request to change the tuning
options. */
goto fail;
}
table->n_buckets = compute_bucket_size (candidate, tuning);
if (!table->n_buckets)
goto fail;
table->bucket = calloc (table->n_buckets, sizeof *table->bucket);
if (table->bucket == NULL)
goto fail;
table->bucket_limit = table->bucket + table->n_buckets;
table->n_buckets_used = 0;
table->n_entries = 0;
table->hasher = hasher;
table->comparator = comparator;
table->data_freer = data_freer;
table->free_entry_list = NULL;
#if USE_OBSTACK
obstack_init (&table->entry_stack);
#endif
return table;
fail:
free (table);
return NULL;
}
/* Make all buckets empty, placing any chained entries on the free list.
Apply the user-specified function data_freer (if any) to the datas of any
affected entries. */
void
hash_clear (Hash_table *table)
{
struct hash_entry *bucket;
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
if (bucket->data)
{
struct hash_entry *cursor;
struct hash_entry *next;
/* Free the bucket overflow. */
for (cursor = bucket->next; cursor; cursor = next)
{
if (table->data_freer)
table->data_freer (cursor->data);
cursor->data = NULL;
next = cursor->next;
/* Relinking is done one entry at a time, as it is to be expected
that overflows are either rare or short. */
cursor->next = table->free_entry_list;
table->free_entry_list = cursor;
}
/* Free the bucket head. */
if (table->data_freer)
table->data_freer (bucket->data);
bucket->data = NULL;
bucket->next = NULL;
}
}
table->n_buckets_used = 0;
table->n_entries = 0;
}
/* Reclaim all storage associated with a hash table. If a data_freer
function has been supplied by the user when the hash table was created,
this function applies it to the data of each entry before freeing that
entry. */
void
hash_free (Hash_table *table)
{
struct hash_entry *bucket;
struct hash_entry *cursor;
struct hash_entry *next;
/* Call the user data_freer function. */
if (table->data_freer && table->n_entries)
{
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
if (bucket->data)
{
for (cursor = bucket; cursor; cursor = cursor->next)
table->data_freer (cursor->data);
}
}
}
#if USE_OBSTACK
obstack_free (&table->entry_stack, NULL);
#else
/* Free all bucket overflowed entries. */
for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
{
for (cursor = bucket->next; cursor; cursor = next)
{
next = cursor->next;
free (cursor);
}
}
/* Also reclaim the internal list of previously freed entries. */
for (cursor = table->free_entry_list; cursor; cursor = next)
{
next = cursor->next;
free (cursor);
}
#endif
/* Free the remainder of the hash table structure. */
free (table->bucket);
free (table);
}
/* Insertion and deletion. */
/* Get a new hash entry for a bucket overflow, possibly by recycling a
previously freed one. If this is not possible, allocate a new one. */
static struct hash_entry *
allocate_entry (Hash_table *table)
{
struct hash_entry *new;
if (table->free_entry_list)
{
new = table->free_entry_list;
table->free_entry_list = new->next;
}
else
{
#if USE_OBSTACK
new = obstack_alloc (&table->entry_stack, sizeof *new);
#else
new = malloc (sizeof *new);
#endif
}
return new;
}
/* Free a hash entry which was part of some bucket overflow,
saving it for later recycling. */
static void
free_entry (Hash_table *table, struct hash_entry *entry)
{
entry->data = NULL;
entry->next = table->free_entry_list;
table->free_entry_list = entry;
}
/* This private function is used to help with insertion and deletion. When
ENTRY matches an entry in the table, return a pointer to the corresponding
user data and set *BUCKET_HEAD to the head of the selected bucket.
Otherwise, return NULL. When DELETE is true and ENTRY matches an entry in
the table, unlink the matching entry. */
static void *
hash_find_entry (Hash_table *table, const void *entry,
struct hash_entry **bucket_head, bool delete)
{
struct hash_entry *bucket = safe_hasher (table, entry);
struct hash_entry *cursor;
*bucket_head = bucket;
/* Test for empty bucket. */
if (bucket->data == NULL)
return NULL;
/* See if the entry is the first in the bucket. */
if (entry == bucket->data || table->comparator (entry, bucket->data))
{
void *data = bucket->data;
if (delete)
{
if (bucket->next)
{
struct hash_entry *next = bucket->next;
/* Bump the first overflow entry into the bucket head, then save
the previous first overflow entry for later recycling. */
*bucket = *next;
free_entry (table, next);
}
else
{
bucket->data = NULL;
}
}
return data;
}
/* Scan the bucket overflow. */
for (cursor = bucket; cursor->next; cursor = cursor->next)
{
if (entry == cursor->next->data
|| table->comparator (entry, cursor->next->data))
{
void *data = cursor->next->data;
if (delete)
{
struct hash_entry *next = cursor->next;
/* Unlink the entry to delete, then save the freed entry for later
recycling. */
cursor->next = next->next;
free_entry (table, next);
}
return data;
}
}
/* No entry found. */
return NULL;
}
/* Internal helper, to move entries from SRC to DST. Both tables must
share the same free entry list. If SAFE, only move overflow
entries, saving bucket heads for later, so that no allocations will
occur. Return false if the free entry list is exhausted and an
allocation fails. */
static bool
transfer_entries (Hash_table *dst, Hash_table *src, bool safe)
{
struct hash_entry *bucket;
struct hash_entry *cursor;
struct hash_entry *next;
for (bucket = src->bucket; bucket < src->bucket_limit; bucket++)
if (bucket->data)
{
void *data;
struct hash_entry *new_bucket;
/* Within each bucket, transfer overflow entries first and
then the bucket head, to minimize memory pressure. After
all, the only time we might allocate is when moving the
bucket head, but moving overflow entries first may create
free entries that can be recycled by the time we finally
get to the bucket head. */
for (cursor = bucket->next; cursor; cursor = next)
{
data = cursor->data;
new_bucket = safe_hasher (dst, data);
next = cursor->next;
if (new_bucket->data)
{
/* Merely relink an existing entry, when moving from a
bucket overflow into a bucket overflow. */
cursor->next = new_bucket->next;
new_bucket->next = cursor;
}
else
{
/* Free an existing entry, when moving from a bucket
overflow into a bucket header. */
new_bucket->data = data;
dst->n_buckets_used++;
free_entry (dst, cursor);
}
}
/* Now move the bucket head. Be sure that if we fail due to
allocation failure that the src table is in a consistent
state. */
data = bucket->data;
bucket->next = NULL;
if (safe)
continue;
new_bucket = safe_hasher (dst, data);
if (new_bucket->data)
{
/* Allocate or recycle an entry, when moving from a bucket
header into a bucket overflow. */
struct hash_entry *new_entry = allocate_entry (dst);
if (new_entry == NULL)
return false;
new_entry->data = data;
new_entry->next = new_bucket->next;
new_bucket->next = new_entry;
}
else
{
/* Move from one bucket header to another. */
new_bucket->data = data;
dst->n_buckets_used++;
}
bucket->data = NULL;
src->n_buckets_used--;
}
return true;
}
/* For an already existing hash table, change the number of buckets through
specifying CANDIDATE. The contents of the hash table are preserved. The
new number of buckets is automatically selected so as to _guarantee_ that
the table may receive at least CANDIDATE different user entries, including
those already in the table, before any other growth of the hash table size
occurs. If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the
exact number of buckets desired. Return true iff the rehash succeeded. */
bool
hash_rehash (Hash_table *table, size_t candidate)
{
Hash_table storage;
Hash_table *new_table;
size_t new_size = compute_bucket_size (candidate, table->tuning);
if (!new_size)
return false;
if (new_size == table->n_buckets)
return true;
new_table = &storage;
new_table->bucket = calloc (new_size, sizeof *new_table->bucket);
if (new_table->bucket == NULL)
return false;
new_table->n_buckets = new_size;
new_table->bucket_limit = new_table->bucket + new_size;
new_table->n_buckets_used = 0;
new_table->n_entries = 0;
new_table->tuning = table->tuning;
new_table->hasher = table->hasher;
new_table->comparator = table->comparator;
new_table->data_freer = table->data_freer;
/* In order for the transfer to successfully complete, we need
additional overflow entries when distinct buckets in the old
table collide into a common bucket in the new table. The worst
case possible is a hasher that gives a good spread with the old
size, but returns a constant with the new size; if we were to
guarantee table->n_buckets_used-1 free entries in advance, then
the transfer would be guaranteed to not allocate memory.
However, for large tables, a guarantee of no further allocation
introduces a lot of extra memory pressure, all for an unlikely
corner case (most rehashes reduce, rather than increase, the
number of overflow entries needed). So, we instead ensure that
the transfer process can be reversed if we hit a memory
allocation failure mid-transfer. */
/* Merely reuse the extra old space into the new table. */
#if USE_OBSTACK
new_table->entry_stack = table->entry_stack;
#endif
new_table->free_entry_list = table->free_entry_list;
if (transfer_entries (new_table, table, false))
{
/* Entries transferred successfully; tie up the loose ends. */
free (table->bucket);
table->bucket = new_table->bucket;
table->bucket_limit = new_table->bucket_limit;
table->n_buckets = new_table->n_buckets;
table->n_buckets_used = new_table->n_buckets_used;
table->free_entry_list = new_table->free_entry_list;
/* table->n_entries and table->entry_stack already hold their value. */
return true;
}
/* We've allocated new_table->bucket (and possibly some entries),
exhausted the free list, and moved some but not all entries into
new_table. We must undo the partial move before returning
failure. The only way to get into this situation is if new_table
uses fewer buckets than the old table, so we will reclaim some
free entries as overflows in the new table are put back into
distinct buckets in the old table.
There are some pathological cases where a single pass through the
table requires more intermediate overflow entries than using two
passes. Two passes give worse cache performance and takes
longer, but at this point, we're already out of memory, so slow
and safe is better than failure. */
table->free_entry_list = new_table->free_entry_list;
if (! (transfer_entries (table, new_table, true)
&& transfer_entries (table, new_table, false)))
abort ();
/* table->n_entries already holds its value. */
free (new_table->bucket);
return false;
}
/* Insert ENTRY into hash TABLE if there is not already a matching entry.
Return -1 upon memory allocation failure.
Return 1 if insertion succeeded.
Return 0 if there is already a matching entry in the table,
and in that case, if MATCHED_ENT is non-NULL, set *MATCHED_ENT
to that entry.
This interface is easier to use than hash_insert when you must
distinguish between the latter two cases. More importantly,
hash_insert is unusable for some types of ENTRY values. When using
hash_insert, the only way to distinguish those cases is to compare
the return value and ENTRY. That works only when you can have two
different ENTRY values that point to data that compares "equal". Thus,
when the ENTRY value is a simple scalar, you must use
hash_insert_if_absent. ENTRY must not be NULL. */
int
hash_insert_if_absent (Hash_table *table, void const *entry,
void const **matched_ent)
{
void *data;
struct hash_entry *bucket;
/* The caller cannot insert a NULL entry, since hash_lookup returns NULL
to indicate "not found", and hash_find_entry uses "bucket->data == NULL"
to indicate an empty bucket. */
if (! entry)
abort ();
/* If there's a matching entry already in the table, return that. */
if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL)
{
if (matched_ent)
*matched_ent = data;
return 0;
}
/* If the growth threshold of the buckets in use has been reached, increase
the table size and rehash. There's no point in checking the number of
entries: if the hashing function is ill-conditioned, rehashing is not
likely to improve it. */
if (table->n_buckets_used
> table->tuning->growth_threshold * table->n_buckets)
{
/* Check more fully, before starting real work. If tuning arguments
became invalid, the second check will rely on proper defaults. */
check_tuning (table);
if (table->n_buckets_used
> table->tuning->growth_threshold * table->n_buckets)
{
const Hash_tuning *tuning = table->tuning;
float candidate =
(tuning->is_n_buckets
? (table->n_buckets * tuning->growth_factor)
: (table->n_buckets * tuning->growth_factor
* tuning->growth_threshold));
if (SIZE_MAX <= candidate)
return -1;
/* If the rehash fails, arrange to return NULL. */
if (!hash_rehash (table, candidate))
return -1;
/* Update the bucket we are interested in. */
if (hash_find_entry (table, entry, &bucket, false) != NULL)
abort ();
}
}
/* ENTRY is not matched, it should be inserted. */
if (bucket->data)
{
struct hash_entry *new_entry = allocate_entry (table);
if (new_entry == NULL)
return -1;
/* Add ENTRY in the overflow of the bucket. */
new_entry->data = (void *) entry;
new_entry->next = bucket->next;
bucket->next = new_entry;
table->n_entries++;
return 1;
}
/* Add ENTRY right in the bucket head. */
bucket->data = (void *) entry;
table->n_entries++;
table->n_buckets_used++;
return 1;
}
/* If ENTRY matches an entry already in the hash table, return the pointer
to the entry from the table. Otherwise, insert ENTRY and return ENTRY.
Return NULL if the storage required for insertion cannot be allocated.
This implementation does not support duplicate entries or insertion of
NULL. */
void *
hash_insert (Hash_table *table, void const *entry)
{
void const *matched_ent;
int err = hash_insert_if_absent (table, entry, &matched_ent);
return (err == -1
? NULL
: (void *) (err == 0 ? matched_ent : entry));
}
/* If ENTRY is already in the table, remove it and return the just-deleted
data (the user may want to deallocate its storage). If ENTRY is not in the
table, don't modify the table and return NULL. */
void *
hash_delete (Hash_table *table, const void *entry)
{
void *data;
struct hash_entry *bucket;
data = hash_find_entry (table, entry, &bucket, true);
if (!data)
return NULL;
table->n_entries--;
if (!bucket->data)
{
table->n_buckets_used--;
/* If the shrink threshold of the buckets in use has been reached,
rehash into a smaller table. */
if (table->n_buckets_used
< table->tuning->shrink_threshold * table->n_buckets)
{
/* Check more fully, before starting real work. If tuning arguments
became invalid, the second check will rely on proper defaults. */
check_tuning (table);
if (table->n_buckets_used
< table->tuning->shrink_threshold * table->n_buckets)
{
const Hash_tuning *tuning = table->tuning;
size_t candidate =
(tuning->is_n_buckets
? table->n_buckets * tuning->shrink_factor
: (table->n_buckets * tuning->shrink_factor
* tuning->growth_threshold));
if (!hash_rehash (table, candidate))
{
/* Failure to allocate memory in an attempt to
shrink the table is not fatal. But since memory
is low, we can at least be kind and free any
spare entries, rather than keeping them tied up
in the free entry list. */
#if ! USE_OBSTACK
struct hash_entry *cursor = table->free_entry_list;
struct hash_entry *next;
while (cursor)
{
next = cursor->next;
free (cursor);
cursor = next;
}
table->free_entry_list = NULL;
#endif
}
}
}
}
return data;
}
/* Testing. */
#if TESTING
void
hash_print (const Hash_table *table)
{
struct hash_entry *bucket = (struct hash_entry *) table->bucket;
for ( ; bucket < table->bucket_limit; bucket++)
{
struct hash_entry *cursor;
if (bucket)
printf ("%lu:\n", (unsigned long int) (bucket - table->bucket));
for (cursor = bucket; cursor; cursor = cursor->next)
{
char const *s = cursor->data;
/* FIXME */
if (s)
printf (" %s\n", s);
}
}
}
#endif /* TESTING */
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