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Diffstat (limited to 'contrib/tar/lib/hash.c')
-rw-r--r-- | contrib/tar/lib/hash.c | 1009 |
1 files changed, 1009 insertions, 0 deletions
diff --git a/contrib/tar/lib/hash.c b/contrib/tar/lib/hash.c new file mode 100644 index 0000000..a94a549 --- /dev/null +++ b/contrib/tar/lib/hash.c @@ -0,0 +1,1009 @@ +/* hash - hashing table processing. + Copyright (C) 1998, 1999, 2000 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 2, 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, write to the Free Software Foundation, + Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ + +/* 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! */ + +#if HAVE_CONFIG_H +# include <config.h> +#endif +#if HAVE_STDLIB_H +# include <stdlib.h> +#endif +#if HAVE_STDBOOL_H +# include <stdbool.h> +#else +typedef enum {false = 0, true = 1} bool; +#endif +#include <stdio.h> +#include <assert.h> + +#ifndef HAVE_DECL_FREE +"this configure-time declaration test was not run" +#endif +#if !HAVE_DECL_FREE +void free (); +#endif + +#ifndef HAVE_DECL_MALLOC +"this configure-time declaration test was not run" +#endif +#if !HAVE_DECL_MALLOC +char *malloc (); +#endif + +#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 + +#include "hash.h" + +/* 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 0.8 +#define DEFAULT_GROWTH_FACTOR 1.414 + +/* 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 0.0 +#define DEFAULT_SHRINK_FACTOR 1.0 + +/* 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. */ + +unsigned +hash_get_n_buckets (const Hash_table *table) +{ + return table->n_buckets; +} + +/* Return the number of slots in use (non-empty buckets). */ + +unsigned +hash_get_n_buckets_used (const Hash_table *table) +{ + return table->n_buckets_used; +} + +/* Return the number of active entries. */ + +unsigned +hash_get_n_entries (const Hash_table *table) +{ + return table->n_entries; +} + +/* Return the length of the longest chain (bucket). */ + +unsigned +hash_get_max_bucket_length (const Hash_table *table) +{ + struct hash_entry *bucket; + unsigned max_bucket_length = 0; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + { + if (bucket->data) + { + struct hash_entry *cursor = bucket; + unsigned 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 *bucket; + unsigned n_buckets_used = 0; + unsigned n_entries = 0; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + { + if (bucket->data) + { + struct hash_entry *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) +{ + unsigned n_entries = hash_get_n_entries (table); + unsigned n_buckets = hash_get_n_buckets (table); + unsigned n_buckets_used = hash_get_n_buckets_used (table); + unsigned max_bucket_length = hash_get_max_bucket_length (table); + + fprintf (stream, "# entries: %u\n", n_entries); + fprintf (stream, "# buckets: %u\n", n_buckets); + fprintf (stream, "# buckets used: %u (%.2f%%)\n", n_buckets_used, + (100.0 * n_buckets_used) / n_buckets); + fprintf (stream, "max bucket length: %u\n", max_bucket_length); +} + +/* 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 *bucket + = table->bucket + table->hasher (entry, table->n_buckets); + struct hash_entry *cursor; + + assert (bucket < table->bucket_limit); + + if (bucket->data == NULL) + return NULL; + + for (cursor = bucket; cursor; cursor = cursor->next) + if (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 or removed. */ + +/* 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 *bucket; + + if (table->n_entries == 0) + return NULL; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + if (bucket->data) + return bucket->data; + + assert (0); + return NULL; +} + +/* 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 *bucket + = table->bucket + table->hasher (entry, table->n_buckets); + struct hash_entry *cursor; + + assert (bucket < table->bucket_limit); + + /* Find next entry in the same bucket. */ + for (cursor = bucket; cursor; cursor = cursor->next) + if (cursor->data == entry && cursor->next) + return cursor->next->data; + + /* 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. */ + +unsigned +hash_get_entries (const Hash_table *table, void **buffer, + unsigned buffer_size) +{ + unsigned counter = 0; + struct hash_entry *bucket; + struct hash_entry *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. */ + +unsigned +hash_do_for_each (const Hash_table *table, Hash_processor processor, + void *processor_data) +{ + unsigned counter = 0; + struct hash_entry *bucket; + struct hash_entry *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." */ + +unsigned +hash_string (const char *string, unsigned n_buckets) +{ +# ifndef CHAR_BIT +# define CHAR_BIT 8 +# endif +# define ROTATE_LEFT(Value, Shift) \ + ((Value) << (Shift) | (Value) >> ((sizeof (unsigned) * CHAR_BIT) - (Shift))) +# define HASH_ONE_CHAR(Value, Byte) \ + ((Byte) + ROTATE_LEFT (Value, 7)) + + unsigned value = 0; + + for (; *string; string++) + value = HASH_ONE_CHAR (value, *(const unsigned char *) string); + return value % n_buckets; + +# undef ROTATE_LEFT +# 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?) */ + +unsigned +hash_string (const char *string, unsigned n_buckets) +{ + unsigned value = 0; + + while (*string) + value = ((value * 31 + (int) *(const unsigned char *) string++) + % 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 +is_prime (unsigned long candidate) +{ + unsigned long divisor = 3; + unsigned long 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 unsigned long +next_prime (unsigned long candidate) +{ + /* Skip small primes. */ + if (candidate < 10) + candidate = 10; + + /* Make it definitely odd. */ + candidate |= 1; + + while (!is_prime (candidate)) + candidate += 2; + + return candidate; +} + +void +hash_reset_tuning (Hash_tuning *tuning) +{ + *tuning = default_tuning; +} + +/* 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; + + if (tuning->growth_threshold > 0.0 + && tuning->growth_threshold < 1.0 + && tuning->growth_factor > 1.0 + && tuning->shrink_threshold >= 0.0 + && tuning->shrink_threshold < 1.0 + && tuning->shrink_factor > tuning->shrink_threshold + && tuning->shrink_factor <= 1.0 + && tuning->shrink_threshold < tuning->growth_threshold) + return true; + + table->tuning = &default_tuning; + return false; +} + +/* 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. + + The user-supplied HASHER function should be provided. It 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 should be provided. It 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. + + 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 (unsigned candidate, const Hash_tuning *tuning, + Hash_hasher hasher, Hash_comparator comparator, + Hash_data_freer data_freer) +{ + Hash_table *table; + struct hash_entry *bucket; + + if (hasher == NULL || comparator == NULL) + return NULL; + + table = (Hash_table *) malloc (sizeof (Hash_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. */ + free (table); + return NULL; + } + + table->n_buckets + = next_prime (tuning->is_n_buckets ? candidate + : (unsigned) (candidate / tuning->growth_threshold)); + + table->bucket = (struct hash_entry *) + malloc (table->n_buckets * sizeof (struct hash_entry)); + if (table->bucket == NULL) + { + free (table); + return NULL; + } + table->bucket_limit = table->bucket + table->n_buckets; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + { + bucket->data = NULL; + bucket->next = NULL; + } + 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; +} + +/* 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; + struct hash_entry *cursor; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + { + if (bucket->data) + { + /* Free the bucket overflow. */ + for (cursor = bucket->next; cursor; cursor = cursor->next) + { + if (table->data_freer) + (*table->data_freer) (cursor->data); + cursor->data = NULL; + + /* 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 reclying 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 = (struct hash_entry *) + obstack_alloc (&table->entry_stack, sizeof (struct hash_entry)); +#else + new = (struct hash_entry *) malloc (sizeof (struct hash_entry)); +#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 + = table->bucket + table->hasher (entry, table->n_buckets); + struct hash_entry *cursor; + + assert (bucket < table->bucket_limit); + *bucket_head = bucket; + + /* Test for empty bucket. */ + if (bucket->data == NULL) + return NULL; + + /* See if the entry is the first in the bucket. */ + if ((*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 ((*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; +} + +/* 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. */ + +bool +hash_rehash (Hash_table *table, unsigned candidate) +{ + Hash_table *new_table; + struct hash_entry *bucket; + struct hash_entry *cursor; + struct hash_entry *next; + + new_table = hash_initialize (candidate, table->tuning, table->hasher, + table->comparator, table->data_freer); + if (new_table == NULL) + return false; + + /* Merely reuse the extra old space into the new table. */ +#if USE_OBSTACK + obstack_free (&new_table->entry_stack, NULL); + new_table->entry_stack = table->entry_stack; +#endif + new_table->free_entry_list = table->free_entry_list; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + if (bucket->data) + for (cursor = bucket; cursor; cursor = next) + { + void *data = cursor->data; + struct hash_entry *new_bucket + = (new_table->bucket + + new_table->hasher (data, new_table->n_buckets)); + + assert (new_bucket < new_table->bucket_limit); + next = cursor->next; + + if (new_bucket->data) + { + if (cursor == bucket) + { + /* Allocate or recycle an entry, when moving from a bucket + header into a bucket overflow. */ + struct hash_entry *new_entry = allocate_entry (new_table); + + if (new_entry == NULL) + return false; + + new_entry->data = data; + new_entry->next = new_bucket->next; + new_bucket->next = new_entry; + } + else + { + /* 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. Also take care of the + simple case of moving from a bucket header into a bucket + header. */ + new_bucket->data = data; + new_table->n_buckets_used++; + if (cursor != bucket) + free_entry (new_table, cursor); + } + } + + 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 already holds its value. */ +#if USE_OBSTACK + table->entry_stack = new_table->entry_stack; +#endif + free (new_table); + + return true; +} + +/* 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. */ + +void * +hash_insert (Hash_table *table, const void *entry) +{ + void *data; + struct hash_entry *bucket; + + assert (entry); /* cannot insert a NULL entry */ + + /* If there's a matching entry already in the table, return that. */ + if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL) + return data; + + /* ENTRY is not matched, it should be inserted. */ + + if (bucket->data) + { + struct hash_entry *new_entry = allocate_entry (table); + + if (new_entry == NULL) + return NULL; + + /* 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 (void *) entry; + } + + /* Add ENTRY right in the bucket head. */ + + bucket->data = (void *) entry; + table->n_entries++; + table->n_buckets_used++; + + /* 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; + unsigned candidate + = (unsigned) (tuning->is_n_buckets + ? (table->n_buckets * tuning->growth_factor) + : (table->n_buckets * tuning->growth_factor + * tuning->growth_threshold)); + + /* If the rehash fails, arrange to return NULL. */ + if (!hash_rehash (table, candidate)) + entry = NULL; + } + } + + return (void *) 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; + unsigned candidate + = (unsigned) (tuning->is_n_buckets + ? table->n_buckets * tuning->shrink_factor + : (table->n_buckets * tuning->shrink_factor + * tuning->growth_threshold)); + + hash_rehash (table, candidate); + } + } + } + + return data; +} + +/* Testing. */ + +#if TESTING + +void +hash_print (const Hash_table *table) +{ + struct hash_entry *bucket; + + for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) + { + struct hash_entry *cursor; + + if (bucket) + printf ("%d:\n", slot); + + for (cursor = bucket; cursor; cursor = cursor->next) + { + char *s = (char *) cursor->data; + /* FIXME */ + printf (" %s\n", s); + } + } +} + +#endif /* TESTING */ |