binutils-gdb/gdb/bcache.c

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/* Implement a cached obstack.
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Written by Fred Fish <fnf@cygnus.com>
Rewritten by Jim Blandy <jimb@cygnus.com>
Copyright 1999 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
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
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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.
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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. */
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#include <stddef.h>
#include <stdlib.h>
#include "defs.h"
#include "obstack.h"
#include "bcache.h"
#include "gdb_string.h" /* For memcpy declaration */
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/* The hash function. */
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unsigned long
hash (void *addr, int length)
{
/* If it's a short string, hash on every character. Otherwise, sample
characters from throughout the string. */
if (length <= 64)
{
char *byte = addr;
unsigned long h = 0;
int i;
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for (i = 0; i < length; i++)
h = h * 65793 ^ (h >> (sizeof (h) * 8 - 6)) ^ byte[i];
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return h;
}
else
{
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char *byte = addr;
int n, i;
unsigned long h = 0;
for (n = i = 0; n < 64; n++)
{
h = h * 65793 + (h >> (sizeof (h) * 8 - 6)) + byte[i];
i = h % length;
}
return h;
}
}
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/* Growing the bcache's hash table. */
/* If the average chain length grows beyond this, then we want to
resize our hash table. */
#define CHAIN_LENGTH_THRESHOLD (5)
static void
expand_hash_table (struct bcache *bcache)
{
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/* A table of good hash table sizes. Whenever we grow, we pick the
next larger size from this table. sizes[i] is close to 1 << (i+10),
so we roughly double the table size each time. After we fall off
the end of this table, we just double. Don't laugh --- there have
been executables sighted with a gigabyte of debug info. */
static unsigned long sizes[] = {
1021, 2053, 4099, 8191, 16381, 32771,
65537, 131071, 262144, 524287, 1048573, 2097143,
4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
268435459, 536870923, 1073741827, 2147483659UL
};
unsigned int new_num_buckets;
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struct bstring **new_buckets;
unsigned int i;
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/* Find the next size. */
new_num_buckets = bcache->num_buckets * 2;
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for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++)
if (sizes[i] > bcache->num_buckets)
{
new_num_buckets = sizes[i];
break;
}
/* Allocate the new table. */
{
size_t new_size = new_num_buckets * sizeof (new_buckets[0]);
new_buckets = (struct bstring **) xmalloc (new_size);
memset (new_buckets, 0, new_size);
bcache->structure_size -= (bcache->num_buckets
* sizeof (bcache->bucket[0]));
bcache->structure_size += new_size;
}
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/* Rehash all existing strings. */
for (i = 0; i < bcache->num_buckets; i++)
{
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struct bstring *s, *next;
for (s = bcache->bucket[i]; s; s = next)
{
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struct bstring **new_bucket;
next = s->next;
new_bucket = &new_buckets[(hash (&s->d.data, s->length)
% new_num_buckets)];
s->next = *new_bucket;
*new_bucket = s;
}
}
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/* Plug in the new table. */
if (bcache->bucket)
free (bcache->bucket);
bcache->bucket = new_buckets;
bcache->num_buckets = new_num_buckets;
}
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/* Looking up things in the bcache. */
/* The number of bytes needed to allocate a struct bstring whose data
is N bytes long. */
#define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
/* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
never seen those bytes before, add a copy of them to BCACHE. In
either case, return a pointer to BCACHE's copy of that string. */
void *
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bcache (void *addr, int length, struct bcache *bcache)
{
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int hash_index;
struct bstring *s;
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/* If our average chain length is too high, expand the hash table. */
if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD)
expand_hash_table (bcache);
bcache->total_count++;
bcache->total_size += length;
hash_index = hash (addr, length) % bcache->num_buckets;
/* Search the hash bucket for a string identical to the caller's. */
for (s = bcache->bucket[hash_index]; s; s = s->next)
if (s->length == length
&& ! memcmp (&s->d.data, addr, length))
return &s->d.data;
/* The user's string isn't in the list. Insert it after *ps. */
{
struct bstring *new
= obstack_alloc (&bcache->cache, BSTRING_SIZE (length));
memcpy (&new->d.data, addr, length);
new->length = length;
new->next = bcache->bucket[hash_index];
bcache->bucket[hash_index] = new;
bcache->unique_count++;
bcache->unique_size += length;
bcache->structure_size += BSTRING_SIZE (length);
return &new->d.data;
}
}
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/* Freeing bcaches. */
/* Free all the storage associated with BCACHE. */
void
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free_bcache (struct bcache *bcache)
{
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obstack_free (&bcache->cache, 0);
free (bcache->bucket);
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/* This isn't necessary, but at least the bcache is always in a
consistent state. */
memset (bcache, 0, sizeof (*bcache));
}
/* Printing statistics. */
static int
compare_ints (const void *ap, const void *bp)
{
/* Because we know we're comparing two ints which are positive,
there's no danger of overflow here. */
return * (int *) ap - * (int *) bp;
}
static void
print_percentage (int portion, int total)
{
if (total == 0)
printf_filtered ("(not applicable)\n");
else
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printf_filtered ("%3d%%\n", portion * 100 / total);
}
/* Print statistics on BCACHE's memory usage and efficacity at
eliminating duplication. NAME should describe the kind of data
BCACHE holds. Statistics are printed using `printf_filtered' and
its ilk. */
void
print_bcache_statistics (struct bcache *c, char *type)
{
int occupied_buckets;
int max_chain_length;
int median_chain_length;
/* Count the number of occupied buckets, and measure chain lengths. */
{
unsigned int b;
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int *chain_length
= (int *) alloca (c->num_buckets * sizeof (*chain_length));
occupied_buckets = 0;
for (b = 0; b < c->num_buckets; b++)
{
struct bstring *s = c->bucket[b];
chain_length[b] = 0;
if (s)
{
occupied_buckets++;
while (s)
{
chain_length[b]++;
s = s->next;
}
}
}
/* To compute the median, we need the set of chain lengths sorted. */
qsort (chain_length, c->num_buckets, sizeof (chain_length[0]),
compare_ints);
if (c->num_buckets > 0)
{
max_chain_length = chain_length[c->num_buckets - 1];
median_chain_length = chain_length[c->num_buckets / 2];
}
else
{
max_chain_length = 0;
median_chain_length = 0;
}
}
printf_filtered (" Cached '%s' statistics:\n", type);
printf_filtered (" Total object count: %ld\n", c->total_count);
printf_filtered (" Unique object count: %lu\n", c->unique_count);
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printf_filtered (" Percentage of duplicates, by count: ");
print_percentage (c->total_count - c->unique_count, c->total_count);
printf_filtered ("\n");
printf_filtered (" Total object size: %ld\n", c->total_size);
printf_filtered (" Unique object size: %ld\n", c->unique_size);
printf_filtered (" Percentage of duplicates, by size: ");
print_percentage (c->total_size - c->unique_size, c->total_size);
printf_filtered ("\n");
printf_filtered (" Total memory used by bcache, including overhead: %ld\n",
c->structure_size);
printf_filtered (" Percentage memory overhead: ");
print_percentage (c->structure_size - c->unique_size, c->unique_size);
printf_filtered (" Net memory savings: ");
print_percentage (c->total_size - c->structure_size, c->total_size);
printf_filtered ("\n");
printf_filtered (" Hash table size: %3d\n", c->num_buckets);
printf_filtered (" Hash table population: ");
print_percentage (occupied_buckets, c->num_buckets);
printf_filtered (" Median hash chain length: %3d\n",
median_chain_length);
printf_filtered (" Average hash chain length: ");
if (c->num_buckets > 0)
printf_filtered ("%3lu\n", c->unique_count / c->num_buckets);
else
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printf_filtered ("(not applicable)\n");
printf_filtered (" Maximum hash chain length: %3d\n", max_chain_length);
printf_filtered ("\n");
}