311 lines
7.9 KiB
C
311 lines
7.9 KiB
C
/* Hash tables.
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Copyright (C) 2000, 2001, 2003 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2, or (at your option) any
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later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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In other words, you are welcome to use, share and improve this program.
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You are forbidden to forbid anyone else to use, share and improve
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what you give them. Help stamp out software-hoarding! */
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#include "config.h"
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#include "system.h"
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#include "hashtable.h"
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/* The code below is a specialization of Vladimir Makarov's expandable
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hash tables (see libiberty/hashtab.c). The abstraction penalty was
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too high to continue using the generic form. This code knows
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intrinsically how to calculate a hash value, and how to compare an
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existing entry with a potential new one. Also, the ability to
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delete members from the table has been removed. */
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static unsigned int calc_hash (const unsigned char *, size_t);
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static void ht_expand (hash_table *);
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static double approx_sqrt (double);
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/* Calculate the hash of the string STR of length LEN. */
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static unsigned int
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calc_hash (const unsigned char *str, size_t len)
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{
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size_t n = len;
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unsigned int r = 0;
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#define HASHSTEP(r, c) ((r) * 67 + ((c) - 113));
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while (n--)
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r = HASHSTEP (r, *str++);
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return r + len;
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#undef HASHSTEP
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}
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/* Initialize an identifier hashtable. */
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hash_table *
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ht_create (unsigned int order)
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{
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unsigned int nslots = 1 << order;
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hash_table *table;
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table = xcalloc (1, sizeof (hash_table));
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/* Strings need no alignment. */
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_obstack_begin (&table->stack, 0, 0,
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(void *(*) (long)) xmalloc,
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(void (*) (void *)) free);
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obstack_alignment_mask (&table->stack) = 0;
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table->entries = xcalloc (nslots, sizeof (hashnode));
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table->nslots = nslots;
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return table;
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}
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/* Frees all memory associated with a hash table. */
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void
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ht_destroy (hash_table *table)
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{
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obstack_free (&table->stack, NULL);
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free (table->entries);
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free (table);
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}
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/* Returns the hash entry for the a STR of length LEN. If that string
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already exists in the table, returns the existing entry, and, if
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INSERT is CPP_ALLOCED, frees the last obstack object. If the
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identifier hasn't been seen before, and INSERT is CPP_NO_INSERT,
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returns NULL. Otherwise insert and returns a new entry. A new
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string is alloced if INSERT is CPP_ALLOC, otherwise INSERT is
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CPP_ALLOCED and the item is assumed to be at the top of the
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obstack. */
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hashnode
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ht_lookup (hash_table *table, const unsigned char *str, size_t len,
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enum ht_lookup_option insert)
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{
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unsigned int hash = calc_hash (str, len);
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unsigned int hash2;
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unsigned int index;
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size_t sizemask;
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hashnode node;
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sizemask = table->nslots - 1;
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index = hash & sizemask;
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table->searches++;
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node = table->entries[index];
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if (node != NULL)
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{
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if (node->hash_value == hash
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&& HT_LEN (node) == (unsigned int) len
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&& !memcmp (HT_STR (node), str, len))
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{
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if (insert == HT_ALLOCED)
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/* The string we search for was placed at the end of the
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obstack. Release it. */
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obstack_free (&table->stack, (void *) str);
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return node;
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}
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/* hash2 must be odd, so we're guaranteed to visit every possible
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location in the table during rehashing. */
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hash2 = ((hash * 17) & sizemask) | 1;
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for (;;)
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{
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table->collisions++;
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index = (index + hash2) & sizemask;
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node = table->entries[index];
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if (node == NULL)
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break;
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if (node->hash_value == hash
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&& HT_LEN (node) == (unsigned int) len
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&& !memcmp (HT_STR (node), str, len))
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{
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if (insert == HT_ALLOCED)
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/* The string we search for was placed at the end of the
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obstack. Release it. */
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obstack_free (&table->stack, (void *) str);
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return node;
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}
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}
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}
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if (insert == HT_NO_INSERT)
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return NULL;
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node = (*table->alloc_node) (table);
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table->entries[index] = node;
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HT_LEN (node) = (unsigned int) len;
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node->hash_value = hash;
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if (insert == HT_ALLOC)
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HT_STR (node) = obstack_copy0 (&table->stack, str, len);
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else
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HT_STR (node) = str;
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if (++table->nelements * 4 >= table->nslots * 3)
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/* Must expand the string table. */
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ht_expand (table);
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return node;
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}
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/* Double the size of a hash table, re-hashing existing entries. */
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static void
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ht_expand (hash_table *table)
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{
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hashnode *nentries, *p, *limit;
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unsigned int size, sizemask;
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size = table->nslots * 2;
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nentries = xcalloc (size, sizeof (hashnode));
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sizemask = size - 1;
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p = table->entries;
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limit = p + table->nslots;
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do
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if (*p)
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{
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unsigned int index, hash, hash2;
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hash = (*p)->hash_value;
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index = hash & sizemask;
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if (nentries[index])
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{
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hash2 = ((hash * 17) & sizemask) | 1;
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do
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{
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index = (index + hash2) & sizemask;
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}
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while (nentries[index]);
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}
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nentries[index] = *p;
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}
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while (++p < limit);
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free (table->entries);
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table->entries = nentries;
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table->nslots = size;
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}
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/* For all nodes in TABLE, callback CB with parameters TABLE->PFILE,
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the node, and V. */
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void
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ht_forall (hash_table *table, ht_cb cb, const void *v)
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{
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hashnode *p, *limit;
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p = table->entries;
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limit = p + table->nslots;
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do
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if (*p)
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{
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if ((*cb) (table->pfile, *p, v) == 0)
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break;
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}
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while (++p < limit);
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}
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/* Dump allocation statistics to stderr. */
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void
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ht_dump_statistics (hash_table *table)
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{
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size_t nelts, nids, overhead, headers;
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size_t total_bytes, longest, sum_of_squares;
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double exp_len, exp_len2, exp2_len;
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hashnode *p, *limit;
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#define SCALE(x) ((unsigned long) ((x) < 1024*10 \
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? (x) \
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: ((x) < 1024*1024*10 \
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? (x) / 1024 \
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: (x) / (1024*1024))))
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#define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
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total_bytes = longest = sum_of_squares = nids = 0;
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p = table->entries;
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limit = p + table->nslots;
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do
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if (*p)
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{
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size_t n = HT_LEN (*p);
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total_bytes += n;
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sum_of_squares += n * n;
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if (n > longest)
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longest = n;
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nids++;
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}
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while (++p < limit);
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nelts = table->nelements;
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overhead = obstack_memory_used (&table->stack) - total_bytes;
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headers = table->nslots * sizeof (hashnode);
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fprintf (stderr, "\nString pool\nentries\t\t%lu\n",
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(unsigned long) nelts);
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fprintf (stderr, "identifiers\t%lu (%.2f%%)\n",
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(unsigned long) nids, nids * 100.0 / nelts);
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fprintf (stderr, "slots\t\t%lu\n",
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(unsigned long) table->nslots);
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fprintf (stderr, "bytes\t\t%lu%c (%lu%c overhead)\n",
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SCALE (total_bytes), LABEL (total_bytes),
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SCALE (overhead), LABEL (overhead));
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fprintf (stderr, "table size\t%lu%c\n",
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SCALE (headers), LABEL (headers));
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exp_len = (double)total_bytes / (double)nelts;
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exp2_len = exp_len * exp_len;
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exp_len2 = (double) sum_of_squares / (double) nelts;
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fprintf (stderr, "coll/search\t%.4f\n",
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(double) table->collisions / (double) table->searches);
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fprintf (stderr, "ins/search\t%.4f\n",
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(double) nelts / (double) table->searches);
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fprintf (stderr, "avg. entry\t%.2f bytes (+/- %.2f)\n",
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exp_len, approx_sqrt (exp_len2 - exp2_len));
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fprintf (stderr, "longest entry\t%lu\n",
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(unsigned long) longest);
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#undef SCALE
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#undef LABEL
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}
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/* Return the approximate positive square root of a number N. This is for
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statistical reports, not code generation. */
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static double
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approx_sqrt (double x)
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{
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double s, d;
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if (x < 0)
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abort ();
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if (x == 0)
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return 0;
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s = x;
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do
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{
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d = (s * s - x) / (2 * s);
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s -= d;
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}
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while (d > .0001);
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return s;
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}
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