X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/mLib/blobdiff_plain/d2a91066c99aebac0e651b09ffd699b17f156f94..03d53b73fc6663cef4493cfda7193c958557c240:/hash.h diff --git a/hash.h b/hash.h new file mode 100644 index 0000000..6d739a7 --- /dev/null +++ b/hash.h @@ -0,0 +1,214 @@ +/* -*-c-*- + * + * $Id: hash.h,v 1.1 1999/08/02 14:45:48 mdw Exp $ + * + * General hashtable infrastructure + * + * (c) 1999 Straylight/Edgeware + */ + +/*----- Licensing notice --------------------------------------------------* + * + * This file is part of the mLib utilities library. + * + * mLib is free software; you can redistribute it and/or modify + * it under the terms of the GNU Library General Public License as + * published by the Free Software Foundation; either version 2 of the + * License, or (at your option) any later version. + * + * mLib 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 Library General Public License for more details. + * + * You should have received a copy of the GNU Library General Public + * License along with mLib; if not, write to the Free + * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +/*----- Revision history --------------------------------------------------* + * + * $Log: hash.h,v $ + * Revision 1.1 1999/08/02 14:45:48 mdw + * Break low-level hashtable code out from sym. + * + */ + +#ifndef HASH_H +#define HASH_H + +#ifdef __cplusplus + extern "C" { +#endif + +/*----- Notes -------------------------------------------------------------* + * + * This isn't a complete implementation of anything. It's a collection of + * useful types and functions which will help when building hashtables of + * things. The general-purpose hashtable is provided by the @sym@ functions. + */ + +/*----- Header files ------------------------------------------------------*/ + +#include + +#ifndef BITS_H +# include "bits.h" +#endif + +/*----- Data structures ---------------------------------------------------*/ + +/* --- Hashtable basics --- * + * + * This contains the bare minimum to actually get anything useful done. In + * particular it doesn't maintain any weighting information: when to extend + * the table is left up to the particular implementation. + */ + +typedef struct hash_table { + uint32 mask; /* Bit mask of hash bits */ + struct hash_base **v; /* Vector of hash bins */ +} hash_table; + +/* --- A hashtable entry --- * + * + * This is the bare minimum of what needs to be remembered in each hashtable + * entry. Comparison of elements is left to the implementation, so I don't + * need to know anything about how to represent hash keys here. + */ + +typedef struct hash_base { + struct hash_base *next; /* Next entry in hash bin */ + uint32 hash; /* Hash value for this entry */ +} hash_base; + +/* --- A hashtable iterator --- */ + +typedef struct hash_iter { + hash_table *t; /* Hashtable being iterated */ + hash_base *p; /* Address of next item to return */ + size_t i; /* Index of next hash bin to use */ +} hash_iter; + +/*----- Functions provided ------------------------------------------------*/ + +/* --- @hash_create@ --- * + * + * Arguments: @hash_table *t@ = pointer to hashtable to initialize + * @size_t n@ = number of bins to allocate (zero initially) + * + * Returns: --- + * + * Use: Initializes a hashtable with a given number of bins. The + * bins are initially empty. The number of bins must be a power + * of two. This is not checked. + */ + +extern void hash_create(hash_table */*t*/, size_t /*n*/); + +/* --- @hash_destroy@ --- * + * + * Arguments: @hash_table *t@ = pointer to hashtable to destroy + * + * Returns: --- + * + * Use: Frees a hashtable. The items are not freed: they are the + * responsibility of the implementation. + */ + +extern void hash_destroy(hash_table */*t*/); + +/* --- @hash_bin@ --- * + * + * Arguments: @hash_table *t@ = pointer to hashtable + * @uint32 hash@ = hash value to look up + * + * Returns: Pointer to the bin's list head. + * + * Use: Given a hash value return the address of the appropriate list + * head. It is safe to remove the current entry from the table. + */ + +#define HASH_BIN(t, hash) ((t)->v + ((hash) & (t)->mask)) + +extern hash_base **hash_bin(hash_table */*t*/, uint32 /*hash*/); + +/* --- @hash_extend@ --- * + * + * Arguments: @hash_table *t@ = pointer to hashtable to extend + * + * Returns: Nonzero if extension was successful. + * + * Use: Extends a hashtable. The number of bins is doubled and the + * entries are redistributed. + */ + +extern int hash_extend(hash_table */*t*/); + +/* --- @hash_remove@ --- * + * + * Arguments: @hash_table *t@ = pointer to hashtable + * @hash_base *p@ = pointer to item to remove + * + * Returns: --- + * + * Use: Removes an item from a hashtable. The item itself is not + * freed, although it is removed from the data structure and is + * safe to free. + */ + +extern void hash_remove(hash_table */*t*/, hash_base */*p*/); + +/* --- @hash_mkiter@ --- * + * + * Arguments: @hash_iter *i@ = pointer to iterator to create + * @hash_table *t@ = pointer to hashtable to iterate + * + * Returns: --- + * + * Use: Initializes a hashtable iterator. + */ + +#define HASH_MKITER(i_, t_) ((i_)->t = (t_), (i_)->p = 0, (i_)->i = 0) + +extern void hash_mkiter(hash_iter */*i*/, hash_table */*t*/); + +/* --- @hash_next@ --- * + * + * Arguments: @hash_iter *i@ = pointer to iterator + * + * Returns: Pointer to the next hashtable entry found, or null. + * + * Use: Returns the next entry from the hashtable. + */ + +#define HASH_NEXT(i_, b_) do { \ + hash_iter *_i = (i_); \ + hash_base *_p; \ + hash_table *_t = _i->t; \ + uint32 _m = _t->mask; \ + \ + for (;;) { \ + if (_i->p) { \ + _p = _i->p; \ + _i->p = _p->next; \ + break; \ + } else if (_i->i > _m) { \ + _p = 0; \ + break; \ + } else \ + _i->p = _t->v[_i->i++]; \ + } \ + (b_) = _p; \ +} while (0) + +extern hash_base *hash_next(hash_iter */*i*/); + +/*----- That's all, folks -------------------------------------------------*/ + +#ifdef __cplusplus + } +#endif + +#endif