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/* Implement a cached obstack.
Written by Fred Fish (fnf@cygnus.com)
Copyright 1995 Free Software Foundation, Inc.
This file is part of GDB.
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.
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. */
#include "defs.h"
#include "obstack.h"
#include "bcache.h"
/* FIXME: Incredibly simplistic hash generator. Probably way too expensive
(consider long strings) and unlikely to have good distribution across hash
values for typical input. */
static unsigned int
hash (bytes, count)
void *bytes;
int count;
{
unsigned int len;
unsigned long hashval;
unsigned int c;
const unsigned char *data = bytes;
hashval = 0;
len = 0;
while (count-- > 0)
{
c = *data++;
hashval += c + (c << 17);
hashval ^= hashval >> 2;
++len;
}
hashval += len + (len << 17);
hashval ^= hashval >> 2;
return (hashval % BCACHE_HASHSIZE);
}
static void *
lookup_cache (bytes, count, hashval, bcachep)
void *bytes;
int count;
int hashval;
struct bcache *bcachep;
{
void *location = NULL;
struct hashlink **hashtablep;
struct hashlink *linkp;
hashtablep = bcachep -> indextable[count];
if (hashtablep != NULL)
{
linkp = hashtablep[hashval];
while (linkp != NULL)
{
if (memcmp (linkp -> data, bytes, count) == 0)
{
location = linkp -> data;
break;
}
linkp = linkp -> next;
}
}
return (location);
}
void *
bcache (bytes, count, bcachep)
void *bytes;
int count;
struct bcache *bcachep;
{
int hashval;
void *location;
struct hashlink *newlink;
struct hashlink **linkpp;
struct hashlink ***hashtablepp;
if (count > BCACHE_MAXLENGTH)
{
/* Rare enough to just stash unique copies */
location = (void *) obstack_alloc (&bcachep->cache, count);
bcachep -> cache_bytes += count;
memcpy (location, bytes, count);
bcachep -> bcache_overflows++;
}
else
{
hashval = hash (bytes, count);
location = lookup_cache (bytes, count, hashval, bcachep);
if (location != NULL)
{
bcachep -> cache_savings += count;
bcachep -> cache_hits++;
}
else
{
bcachep -> cache_misses++;
hashtablepp = &bcachep -> indextable[count];
if (*hashtablepp == NULL)
{
*hashtablepp = (struct hashlink **)
obstack_alloc (&bcachep->cache, BCACHE_HASHSIZE * sizeof (struct hashlink *));
bcachep -> cache_bytes += sizeof (struct hashlink *);
memset (*hashtablepp, 0, BCACHE_HASHSIZE * sizeof (struct hashlink *));
}
linkpp = &(*hashtablepp)[hashval];
newlink = (struct hashlink *)
obstack_alloc (&bcachep->cache, sizeof (struct hashlink *) + count);
bcachep -> cache_bytes += sizeof (struct hashlink *) + count;
memcpy (newlink -> data, bytes, count);
newlink -> next = *linkpp;
*linkpp = newlink;
location = newlink -> data;
}
}
return (location);
}
#if MAINTENANCE_CMDS
void
print_bcache_statistics (bcachep, id)
struct bcache *bcachep;
char *id;
{
struct hashlink **hashtablep;
struct hashlink *linkp;
int tidx, tcount, hidx, hcount, lcount, lmax, temp, lmaxt, lmaxh;
for (lmax = lcount = tcount = hcount = tidx = 0; tidx < BCACHE_MAXLENGTH; tidx++)
{
hashtablep = bcachep -> indextable[tidx];
if (hashtablep != NULL)
{
tcount++;
for (hidx = 0; hidx < BCACHE_HASHSIZE; hidx++)
{
linkp = hashtablep[hidx];
if (linkp != NULL)
{
hcount++;
for (temp = 0; linkp != NULL; linkp = linkp -> next)
{
lcount++;
temp++;
}
if (temp > lmax)
{
lmax = temp;
lmaxt = tidx;
lmaxh = hidx;
}
}
}
}
}
printf_filtered (" Cached '%s' statistics:\n", id);
printf_filtered (" Cache hits: %d\n", bcachep -> cache_hits);
printf_filtered (" Cache misses: %d\n", bcachep -> cache_misses);
printf_filtered (" Cache hit ratio: %d%%\n", ((bcachep -> cache_hits) * 100) / (bcachep -> cache_hits + bcachep -> cache_misses));
printf_filtered (" Space used for caching: %d\n", bcachep -> cache_bytes);
printf_filtered (" Space saved by cache hits: %d\n", bcachep -> cache_savings);
printf_filtered (" Number of bcache overflows: %d\n", bcachep -> bcache_overflows);
printf_filtered (" Number of index buckets used: %d\n", tcount);
printf_filtered (" Number of hash table buckets used: %d\n", hcount);
printf_filtered (" Number of chained items: %d\n", lcount);
printf_filtered (" Average hash table population: %d%%\n",
(hcount * 100) / (tcount * BCACHE_HASHSIZE));
printf_filtered (" Average chain length %d\n", lcount / hcount);
printf_filtered (" Maximum chain length %d at %d:%d\n", lmax, lmaxt, lmaxh);
}
#endif /* MAINTENANCE_CMDS */
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