293 lines
8.3 KiB
C
293 lines
8.3 KiB
C
/* Implement a cached obstack.
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Written by Fred Fish <fnf@cygnus.com>
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Rewritten by Jim Blandy <jimb@cygnus.com>
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Copyright 1999, 2000 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any 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, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <stddef.h>
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#include <stdlib.h>
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#include "defs.h"
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#include "obstack.h"
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#include "bcache.h"
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#include "gdb_string.h" /* For memcpy declaration */
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/* The old hash function was stolen from SDBM. This is what DB 3.0 uses now,
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* and is better than the old one.
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*/
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unsigned long
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hash(const void *addr, int length)
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{
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const unsigned char *k, *e;
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unsigned long h;
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k = (const unsigned char *)addr;
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e = k+length;
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for (h=0; k< e;++k)
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{
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h *=16777619;
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h ^= *k;
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}
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return (h);
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}
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/* Growing the bcache's hash table. */
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/* If the average chain length grows beyond this, then we want to
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resize our hash table. */
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#define CHAIN_LENGTH_THRESHOLD (5)
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static void
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expand_hash_table (struct bcache *bcache)
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{
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/* A table of good hash table sizes. Whenever we grow, we pick the
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next larger size from this table. sizes[i] is close to 1 << (i+10),
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so we roughly double the table size each time. After we fall off
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the end of this table, we just double. Don't laugh --- there have
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been executables sighted with a gigabyte of debug info. */
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static unsigned long sizes[] = {
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1021, 2053, 4099, 8191, 16381, 32771,
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65537, 131071, 262144, 524287, 1048573, 2097143,
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4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
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268435459, 536870923, 1073741827, 2147483659UL
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};
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unsigned int new_num_buckets;
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struct bstring **new_buckets;
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unsigned int i;
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/* Find the next size. */
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new_num_buckets = bcache->num_buckets * 2;
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for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++)
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if (sizes[i] > bcache->num_buckets)
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{
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new_num_buckets = sizes[i];
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break;
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}
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/* Allocate the new table. */
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{
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size_t new_size = new_num_buckets * sizeof (new_buckets[0]);
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new_buckets = (struct bstring **) xmalloc (new_size);
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memset (new_buckets, 0, new_size);
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bcache->structure_size -= (bcache->num_buckets
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* sizeof (bcache->bucket[0]));
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bcache->structure_size += new_size;
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}
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/* Rehash all existing strings. */
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for (i = 0; i < bcache->num_buckets; i++)
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{
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struct bstring *s, *next;
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for (s = bcache->bucket[i]; s; s = next)
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{
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struct bstring **new_bucket;
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next = s->next;
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new_bucket = &new_buckets[(hash (&s->d.data, s->length)
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% new_num_buckets)];
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s->next = *new_bucket;
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*new_bucket = s;
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}
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}
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/* Plug in the new table. */
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if (bcache->bucket)
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xfree (bcache->bucket);
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bcache->bucket = new_buckets;
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bcache->num_buckets = new_num_buckets;
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}
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/* Looking up things in the bcache. */
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/* The number of bytes needed to allocate a struct bstring whose data
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is N bytes long. */
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#define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
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/* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
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never seen those bytes before, add a copy of them to BCACHE. In
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either case, return a pointer to BCACHE's copy of that string. */
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void *
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bcache (const void *addr, int length, struct bcache *bcache)
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{
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int hash_index;
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struct bstring *s;
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/* If our average chain length is too high, expand the hash table. */
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if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD)
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expand_hash_table (bcache);
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bcache->total_count++;
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bcache->total_size += length;
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hash_index = hash (addr, length) % bcache->num_buckets;
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/* Search the hash bucket for a string identical to the caller's. */
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for (s = bcache->bucket[hash_index]; s; s = s->next)
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if (s->length == length
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&& ! memcmp (&s->d.data, addr, length))
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return &s->d.data;
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/* The user's string isn't in the list. Insert it after *ps. */
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{
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struct bstring *new
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= obstack_alloc (&bcache->cache, BSTRING_SIZE (length));
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memcpy (&new->d.data, addr, length);
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new->length = length;
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new->next = bcache->bucket[hash_index];
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bcache->bucket[hash_index] = new;
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bcache->unique_count++;
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bcache->unique_size += length;
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bcache->structure_size += BSTRING_SIZE (length);
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return &new->d.data;
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}
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}
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/* Freeing bcaches. */
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/* Free all the storage associated with BCACHE. */
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void
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free_bcache (struct bcache *bcache)
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{
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obstack_free (&bcache->cache, 0);
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if (bcache->bucket)
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xfree (bcache->bucket);
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/* This isn't necessary, but at least the bcache is always in a
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consistent state. */
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memset (bcache, 0, sizeof (*bcache));
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}
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/* Printing statistics. */
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static int
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compare_ints (const void *ap, const void *bp)
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{
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/* Because we know we're comparing two ints which are positive,
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there's no danger of overflow here. */
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return * (int *) ap - * (int *) bp;
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}
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static void
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print_percentage (int portion, int total)
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{
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if (total == 0)
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printf_filtered ("(not applicable)\n");
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else
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printf_filtered ("%3d%%\n", portion * 100 / total);
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}
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/* Print statistics on BCACHE's memory usage and efficacity at
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eliminating duplication. NAME should describe the kind of data
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BCACHE holds. Statistics are printed using `printf_filtered' and
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its ilk. */
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void
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print_bcache_statistics (struct bcache *c, char *type)
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{
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int occupied_buckets;
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int max_chain_length;
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int median_chain_length;
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/* Count the number of occupied buckets, and measure chain lengths. */
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{
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unsigned int b;
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int *chain_length
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= (int *) alloca (c->num_buckets * sizeof (*chain_length));
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occupied_buckets = 0;
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for (b = 0; b < c->num_buckets; b++)
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{
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struct bstring *s = c->bucket[b];
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chain_length[b] = 0;
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if (s)
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{
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occupied_buckets++;
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while (s)
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{
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chain_length[b]++;
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s = s->next;
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}
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}
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}
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/* To compute the median, we need the set of chain lengths sorted. */
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qsort (chain_length, c->num_buckets, sizeof (chain_length[0]),
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compare_ints);
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if (c->num_buckets > 0)
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{
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max_chain_length = chain_length[c->num_buckets - 1];
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median_chain_length = chain_length[c->num_buckets / 2];
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}
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else
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{
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max_chain_length = 0;
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median_chain_length = 0;
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}
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}
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printf_filtered (" Cached '%s' statistics:\n", type);
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printf_filtered (" Total object count: %ld\n", c->total_count);
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printf_filtered (" Unique object count: %lu\n", c->unique_count);
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printf_filtered (" Percentage of duplicates, by count: ");
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print_percentage (c->total_count - c->unique_count, c->total_count);
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printf_filtered ("\n");
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printf_filtered (" Total object size: %ld\n", c->total_size);
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printf_filtered (" Unique object size: %ld\n", c->unique_size);
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printf_filtered (" Percentage of duplicates, by size: ");
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print_percentage (c->total_size - c->unique_size, c->total_size);
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printf_filtered ("\n");
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printf_filtered (" Total memory used by bcache, including overhead: %ld\n",
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c->structure_size);
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printf_filtered (" Percentage memory overhead: ");
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print_percentage (c->structure_size - c->unique_size, c->unique_size);
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printf_filtered (" Net memory savings: ");
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print_percentage (c->total_size - c->structure_size, c->total_size);
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printf_filtered ("\n");
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printf_filtered (" Hash table size: %3d\n", c->num_buckets);
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printf_filtered (" Hash table population: ");
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print_percentage (occupied_buckets, c->num_buckets);
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printf_filtered (" Median hash chain length: %3d\n",
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median_chain_length);
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printf_filtered (" Average hash chain length: ");
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if (c->num_buckets > 0)
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printf_filtered ("%3lu\n", c->unique_count / c->num_buckets);
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else
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printf_filtered ("(not applicable)\n");
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printf_filtered (" Maximum hash chain length: %3d\n", max_chain_length);
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printf_filtered ("\n");
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}
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