diff options
Diffstat (limited to 'gdb/bcache.c')
| -rw-r--r-- | gdb/bcache.c | 293 |
1 files changed, 293 insertions, 0 deletions
diff --git a/gdb/bcache.c b/gdb/bcache.c new file mode 100644 index 00000000000..73b86e8cf53 --- /dev/null +++ b/gdb/bcache.c @@ -0,0 +1,293 @@ +/* Implement a cached obstack. + Written by Fred Fish <fnf@cygnus.com> + Rewritten by Jim Blandy <jimb@cygnus.com> + + Copyright 1999, 2000, 2002 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" +#include "gdb_string.h" /* For memcpy declaration */ + +#include <stddef.h> +#include <stdlib.h> + +/* The old hash function was stolen from SDBM. This is what DB 3.0 uses now, + * and is better than the old one. + */ + +unsigned long +hash(const void *addr, int length) +{ + const unsigned char *k, *e; + unsigned long h; + + k = (const unsigned char *)addr; + e = k+length; + for (h=0; k< e;++k) + { + h *=16777619; + h ^= *k; + } + return (h); +} + +/* 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) +{ + /* 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; + struct bstring **new_buckets; + unsigned int i; + + /* Find the next size. */ + new_num_buckets = bcache->num_buckets * 2; + 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; + } + + /* Rehash all existing strings. */ + for (i = 0; i < bcache->num_buckets; i++) + { + struct bstring *s, *next; + + for (s = bcache->bucket[i]; s; s = 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; + } + } + + /* Plug in the new table. */ + if (bcache->bucket) + xfree (bcache->bucket); + bcache->bucket = new_buckets; + bcache->num_buckets = new_num_buckets; +} + + +/* 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 (const void *addr, int length, struct bcache *bcache) +{ + int hash_index; + struct bstring *s; + + /* 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; + } +} + + +/* Freeing bcaches. */ + +/* Free all the storage associated with BCACHE. */ +void +free_bcache (struct bcache *bcache) +{ + obstack_free (&bcache->cache, 0); + if (bcache->bucket) + xfree (bcache->bucket); + + /* 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 + 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; + 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); + 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 + printf_filtered ("(not applicable)\n"); + printf_filtered (" Maximum hash chain length: %3d\n", max_chain_length); + printf_filtered ("\n"); +} |