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Diffstat (limited to 'misc/hsearch_r.c')
| -rw-r--r-- | misc/hsearch_r.c | 229 |
1 files changed, 229 insertions, 0 deletions
diff --git a/misc/hsearch_r.c b/misc/hsearch_r.c new file mode 100644 index 0000000000..5ea1d5e6c8 --- /dev/null +++ b/misc/hsearch_r.c @@ -0,0 +1,229 @@ +/* Copyright (C) 1993, 1995 Free Software Foundation, Inc. +Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu> +This file is part of the GNU C Library. + +The GNU C Library 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. + +The GNU C Library 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 the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, +Boston, MA 02111-1307, USA. */ + +#include <errno.h> +#include <malloc.h> +#include <string.h> + +#include <search.h> + +/* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986 + [Knuth] The Art of Computer Programming, part 3 (6.4) */ + + +/* The reentrent version has no static variables to maintain the state. + Instead the interface of all functions is extended to take an argument + which describes the current status. */ +typedef struct _ENTRY +{ + int used; + ENTRY entry; +} +_ENTRY; + + +/* For the used double hash method the table size has to be a prime. To + correct the user given table size we need a prime test. This trivial + algorithm is adequate because + a) the code is (most probably) called a few times per program run and + b) the number is small because the table must fit in the core */ +static int +isprime (number) + unsigned int number; +{ + /* no even number will be passed */ + unsigned int div = 3; + + while (div * div < number && number % div != 0) + div += 2; + + return number % div != 0; +} + + +/* Before using the hash table we must allocate memory for it. + Test for an existing table are done. We allocate one element + more as the found prime number says. This is done for more effective + indexing as explained in the comment for the hsearch function. + The contents of the table is zeroed, especially the field used + becomes zero. */ +int +hcreate_r (nel, htab) + unsigned int nel; + struct hsearch_data *htab; +{ + /* Test for correct arguments. */ + if (htab == NULL) + { + errno = EINVAL; + return 0; + } + + /* There is still another table active. Return with error. */ + if (htab->table != NULL) + return 0; + + /* Change nel to the first prime number not smaller as nel. */ + nel |= 1; /* make odd */ + while (!isprime (nel)) + nel += 2; + + htab->size = nel; + htab->filled = 0; + + /* allocate memory and zero out */ + htab->table = (_ENTRY *) calloc (htab->size + 1, sizeof (_ENTRY)); + if (htab->table == NULL) + return 0; + + /* everything went alright */ + return 1; +} + + +/* After using the hash table it has to be destroyed. The used memory can + be freed and the local static variable can be marked as not used. */ +void +hdestroy_r (htab) + struct hsearch_data *htab; +{ + /* Test for correct arguments. */ + if (htab == NULL) + { + errno = EINVAL; + return; + } + + if (htab->table != NULL) + /* free used memory */ + free (htab->table); + + /* the sign for an existing table is an value != NULL in htable */ + htab->table = NULL; +} + + +/* This is the search function. It uses double hashing with open adressing. + The argument item.key has to be a pointer to an zero terminated, most + probably strings of chars. The function for generating a number of the + strings is simple but fast. It can be replaced by a more complex function + like ajw (see [Aho,Sethi,Ullman]) if the needs are shown. + + We use an trick to speed up the lookup. The table is created by hcreate + with one more element available. This enables us to use the index zero + special. This index will never be used because we store the first hash + index in the field used where zero means not used. Every other value + means used. The used field can be used as a first fast comparison for + equality of the stored and the parameter value. This helps to prevent + unnecessary expensive calls of strcmp. */ +int +hsearch_r (item, action, retval, htab) + ENTRY item; + ACTION action; + ENTRY **retval; + struct hsearch_data *htab; +{ + unsigned int hval; + unsigned int count; + unsigned int len = strlen (item.key); + unsigned int idx; + + /* If table is full and another entry should be entered return with + error. */ + if (action == ENTER && htab->filled == htab->size) + { + errno = ENOMEM; + *retval = NULL; + return 0; + } + + /* Compute an value for the given string. Perhaps use a better method. */ + hval = len; + count = len; + while (count-- > 0) + { + hval <<= 4; + hval += item.key[count]; + } + + /* First hash function: simply take the modul but prevent zero. */ + hval %= htab->size; + if (hval == 0) + ++hval; + + /* The first index tried. */ + idx = hval; + + if (htab->table[idx].used) + { + /* Further action might be required according to the action value. */ + unsigned hval2; + + if (htab->table[idx].used == hval + && strcmp (item.key, htab->table[idx].entry.key) == 0) + { + if (action == ENTER) + htab->table[idx].entry.data = item.data; + + *retval = &htab->table[idx].entry; + return 1; + } + + /* Second hash function, as suggested in [Knuth] */ + hval2 = 1 + hval % (htab->size - 2); + + do + { + /* Because SIZE is prime this guarantees to step through all + available indeces. */ + if (idx <= hval2) + idx = htab->size + idx - hval2; + else + idx -= hval2; + + /* If entry is found use it. */ + if (htab->table[idx].used == hval + && strcmp (item.key, htab->table[idx].entry.key) == 0) + { + if (action == ENTER) + htab->table[idx].entry.data = item.data; + + *retval = &htab->table[idx].entry; + return 1; + } + } + while (htab->table[idx].used); + } + + /* An empty bucket has been found. */ + if (action == ENTER) + { + htab->table[idx].used = hval; + htab->table[idx].entry = item; + + ++htab->filled; + + *retval = &htab->table[idx].entry; + return 1; + } + + errno = ESRCH; + *retval = NULL; + return 0; +} |