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Diffstat (limited to 'gdb/bcache.h')
| -rw-r--r-- | gdb/bcache.h | 130 |
1 files changed, 0 insertions, 130 deletions
diff --git a/gdb/bcache.h b/gdb/bcache.h deleted file mode 100644 index 6b32c577d4f..00000000000 --- a/gdb/bcache.h +++ /dev/null @@ -1,130 +0,0 @@ -/* Include file cached obstack implementation. - Written by Fred Fish <fnf@cygnus.com> - Rewritten by Jim Blandy <jimb@cygnus.com> - Copyright 1999, 2000 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. */ - -#ifndef BCACHE_H -#define BCACHE_H 1 - -/* A bcache is a data structure for factoring out duplication in - read-only structures. You give the bcache some string of bytes S. - If the bcache already contains a copy of S, it hands you back a - pointer to its copy. Otherwise, it makes a fresh copy of S, and - hands you back a pointer to that. In either case, you can throw - away your copy of S, and use the bcache's. - - The "strings" in question are arbitrary strings of bytes --- they - can contain zero bytes. You pass in the length explicitly when you - call the bcache function. - - This means that you can put ordinary C objects in a bcache. - However, if you do this, remember that structs can contain `holes' - between members, added for alignment. These bytes usually contain - garbage. If you try to bcache two objects which are identical from - your code's point of view, but have different garbage values in the - structure's holes, then the bcache will treat them as separate - strings, and you won't get the nice elimination of duplicates you - were hoping for. So, remember to memset your structures full of - zeros before bcaching them! - - You shouldn't modify the strings you get from a bcache, because: - - - You don't necessarily know who you're sharing space with. If I - stick eight bytes of text in a bcache, and then stick an - eight-byte structure in the same bcache, there's no guarantee - those two objects don't actually comprise the same sequence of - bytes. If they happen to, the bcache will use a single byte - string for both of them. Then, modifying the structure will - change the string. In bizarre ways. - - - Even if you know for some other reason that all that's okay, - there's another problem. A bcache stores all its strings in a - hash table. If you modify a string's contents, you will probably - change its hash value. This means that the modified string is - now in the wrong place in the hash table, and future bcache - probes will never find it. So by mutating a string, you give up - any chance of sharing its space with future duplicates. */ - - -/* The type used to hold a single bcache string. The user data is - stored in d.data. Since it can be any type, it needs to have the - same alignment as the most strict alignment of any type on the host - machine. I don't know of any really correct way to do this in - stock ANSI C, so just do it the same way obstack.h does. - - It would be nicer to have this stuff hidden away in bcache.c, but - struct objstack contains a struct bcache directly --- not a pointer - to one --- and then the memory-mapped stuff makes this a real pain. - We don't strictly need to expose struct bstring, but it's better to - have it all in one place. */ - -struct bstring { - struct bstring *next; - size_t length; - - union - { - char data[1]; - double dummy; - } - d; -}; - - -/* The structure for a bcache itself. - To initialize a bcache, just fill it with zeros. */ -struct bcache { - /* All the bstrings are allocated here. */ - struct obstack cache; - - /* How many hash buckets we're using. */ - unsigned int num_buckets; - - /* Hash buckets. This table is allocated using malloc, so when we - grow the table we can return the old table to the system. */ - struct bstring **bucket; - - /* Statistics. */ - unsigned long unique_count; /* number of unique strings */ - long total_count; /* total number of strings cached, including dups */ - long unique_size; /* size of unique strings, in bytes */ - long total_size; /* total number of bytes cached, including dups */ - long structure_size; /* total size of bcache, including infrastructure */ -}; - - -/* 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. */ -extern void *bcache (void *addr, int length, struct bcache *bcache); - -/* Free all the storage that BCACHE refers to. The result is a valid, - but empty, bcache. This does not free BCACHE itself, since that - might be part of some larger object. */ -extern void free_bcache (struct bcache *bcache); - -/* Print statistics on BCACHE's memory usage and efficacity at - eliminating duplication. TYPE should be a string describing the - kind of data BCACHE holds. Statistics are printed using - `printf_filtered' and its ilk. */ -extern void print_bcache_statistics (struct bcache *bcache, char *type); -/* The hash function */ -extern unsigned long hash(void *addr, int length); -#endif /* BCACHE_H */ |