/* Implement a cached obstack.
- Written by Fred Fish (fnf@cygnus.com)
- Copyright 1995, 1998 Free Software Foundation, Inc.
+ Written by Fred Fish <fnf@cygnus.com>
+ Rewritten by Jim Blandy <jimb@cygnus.com>
+ Copyright 1999 Free Software Foundation, Inc.
This file is part of GDB.
Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
+#include <stddef.h>
+#include <stdlib.h>
+
#include "defs.h"
#include "obstack.h"
#include "bcache.h"
#include "gdb_string.h" /* For memcpy declaration */
-/* Prototypes for local functions. */
-static unsigned int hash PARAMS ((void *, int));
+\f
+/* The hash function. */
-static void *lookup_cache PARAMS ((void *, int, int, struct bcache *));
+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;
-/* FIXME: Incredibly simplistic hash generator. Probably way too expensive
- (consider long strings) and unlikely to have good distribution across hash
- values for typical input. */
+ for (i = 0; i < length; i++)
+ h = h * 65793 ^ (h >> (sizeof (h) * 8 - 6)) ^ byte[i];
-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)
+ return h;
+ }
+ else
{
- c = *data++;
- hashval += c + (c << 17);
- hashval ^= hashval >> 2;
- ++len;
+ 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;
}
- 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;
+\f
+/* 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)
{
- void *location = NULL;
- struct hashlink **hashtablep;
- struct hashlink *linkp;
+ /* 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
+ };
+ int new_num_buckets;
+ struct bstring **new_buckets;
+ int i;
+
+ /* Find the next size. */
+ for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++)
+ if (sizes[i] > bcache->num_buckets)
+ {
+ new_num_buckets = sizes[i];
+ break;
+ }
+ if (i >= (sizeof (sizes) / sizeof (sizes[0])))
+ new_num_buckets = bcache->num_buckets * 2;
+
+ /* 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;
+ }
- hashtablep = bcachep->indextable[count];
- if (hashtablep != NULL)
+ /* Rehash all existing strings. */
+ for (i = 0; i < bcache->num_buckets; i++)
{
- linkp = hashtablep[hashval];
- while (linkp != NULL)
+ struct bstring *s, *next;
+
+ for (s = bcache->bucket[i]; s; s = next)
{
- if (memcmp (BCACHE_DATA (linkp), bytes, count) == 0)
- {
- location = BCACHE_DATA (linkp);
- break;
- }
- linkp = linkp->next;
+ 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;
}
}
- return (location);
+
+ /* Plug in the new table. */
+ if (bcache->bucket)
+ free (bcache->bucket);
+ bcache->bucket = new_buckets;
+ bcache->num_buckets = new_num_buckets;
}
+\f
+/* 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 *
-bcache (bytes, count, bcachep)
- void *bytes;
- int count;
- struct bcache *bcachep;
+bcache (void *addr, int length, struct bcache *bcache)
{
- int hashval;
- void *location;
- struct hashlink *newlink;
- struct hashlink **linkpp;
- struct hashlink ***hashtablepp;
+ int hash_index;
+ struct bstring *s;
- 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 += BCACHE_HASHSIZE * sizeof (struct hashlink *);
- memset (*hashtablepp, 0, BCACHE_HASHSIZE * sizeof (struct hashlink *));
- }
- linkpp = &(*hashtablepp)[hashval];
- newlink = (struct hashlink *)
- obstack_alloc (&bcachep->cache, BCACHE_DATA_ALIGNMENT + count);
- bcachep->cache_bytes += BCACHE_DATA_ALIGNMENT + count;
- memcpy (BCACHE_DATA (newlink), bytes, count);
- newlink->next = *linkpp;
- *linkpp = newlink;
- location = BCACHE_DATA (newlink);
- }
- }
- return (location);
+ /* 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;
+ }
}
+\f
+/* Freeing bcaches. */
+
+/* Free all the storage associated with BCACHE. */
void
-print_bcache_statistics (bcachep, id)
- struct bcache *bcachep;
- char *id;
+free_bcache (struct bcache *bcache)
{
- struct hashlink **hashtablep;
- struct hashlink *linkp;
- int tidx, tcount, hidx, hcount, lcount, lmax, temp, lmaxt, lmaxh;
+ obstack_free (&bcache->cache, 0);
+ free (bcache->bucket);
- 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: ");
- if (bcachep->cache_hits + bcachep->cache_misses > 0)
- {
- printf_filtered ("%d%%\n", ((bcachep->cache_hits) * 100) /
- (bcachep->cache_hits + bcachep->cache_misses));
- }
- else
- {
- printf_filtered ("(not applicable)\n");
- }
- 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: ");
- if (tcount > 0)
- {
- printf_filtered ("%d%%\n", (hcount * 100) / (tcount * BCACHE_HASHSIZE));
- }
+ /* This isn't necessary, but at least the bcache is always in a
+ consistent state. */
+ memset (bcache, 0, sizeof (*bcache));
+}
+
+
+\f
+/* 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
- {
- printf_filtered ("(not applicable)\n");
- }
- printf_filtered (" Average chain length ");
- if (hcount > 0)
- {
- printf_filtered ("%d\n", lcount / hcount);
- }
+ 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. */
+ {
+ int b;
+ 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: %ld\n", c->unique_count);
+ 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 ("%3ld\n", c->unique_count / c->num_buckets);
else
- {
- printf_filtered ("(not applicable)\n");
- }
- printf_filtered (" Maximum chain length %d at %d:%d\n", lmax, lmaxt, lmaxh);
+ printf_filtered ("(not applicable)\n");
+ printf_filtered (" Maximum hash chain length: %3d\n", max_chain_length);
+ printf_filtered ("\n");
}
projects / deliverable / binutils-gdb.git / blobdiff