third-party-mirror / GRTEv4 / 262be5abc585813b1766119db73641d44ba3741e / . / google3 / third_party / grte / v4_src / glibc-2.19 / misc / hsearch_r.c

/* Copyright (C) 1993-2014 Free Software Foundation, Inc. | |

This file is part of the GNU C Library. | |

Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1993. | |

The GNU C Library is free software; you can redistribute it and/or | |

modify it under the terms of the GNU Lesser General Public | |

License as published by the Free Software Foundation; either | |

version 2.1 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 | |

Lesser General Public License for more details. | |

You should have received a copy of the GNU Lesser General Public | |

License along with the GNU C Library; if not, see | |

<http://www.gnu.org/licenses/>. */ | |

#include <errno.h> | |

#include <malloc.h> | |

#include <string.h> | |

#include <stdint.h> | |

#include <search.h> | |

/* [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986 | |

[Knuth] The Art of Computer Programming, part 3 (6.4) */ | |

/* The reentrant 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 | |

{ | |

unsigned 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 (unsigned int number) | |

{ | |

/* no even number will be passed */ | |

for (unsigned int div = 3; div <= number / div; div += 2) | |

if (number % div == 0) | |

return 0; | |

return 1; | |

} | |

/* 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) | |

size_t nel; | |

struct hsearch_data *htab; | |

{ | |

/* Test for correct arguments. */ | |

if (htab == NULL) | |

{ | |

__set_errno (EINVAL); | |

return 0; | |

} | |

/* There is still another table active. Return with error. */ | |

if (htab->table != NULL) | |

return 0; | |

/* We need a size of at least 3. Otherwise the hash functions we | |

use will not work. */ | |

if (nel < 3) | |

nel = 3; | |

/* Change nel to the first prime number in the range [nel, UINT_MAX - 2], | |

The '- 2' means 'nel += 2' cannot overflow. */ | |

for (nel |= 1; ; nel += 2) | |

{ | |

if (UINT_MAX - 2 < nel) | |

{ | |

__set_errno (ENOMEM); | |

return 0; | |

} | |

if (isprime (nel)) | |

break; | |

} | |

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; | |

} | |

libc_hidden_def (hcreate_r) | |

/* 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) | |

{ | |

__set_errno (EINVAL); | |

return; | |

} | |

/* Free used memory. */ | |

free (htab->table); | |

/* the sign for an existing table is an value != NULL in htable */ | |

htab->table = NULL; | |

} | |

libc_hidden_def (hdestroy_r) | |

/* This is the search function. It uses double hashing with open addressing. | |

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; | |

/* 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]; | |

} | |

if (hval == 0) | |

++hval; | |

/* First hash function: simply take the modul but prevent zero. */ | |

idx = hval % htab->size + 1; | |

if (htab->table[idx].used) | |

{ | |

/* Further action might be required according to the action value. */ | |

if (htab->table[idx].used == hval | |

&& strcmp (item.key, htab->table[idx].entry.key) == 0) | |

{ | |

*retval = &htab->table[idx].entry; | |

return 1; | |

} | |

/* Second hash function, as suggested in [Knuth] */ | |

unsigned int hval2 = 1 + hval % (htab->size - 2); | |

unsigned int first_idx = idx; | |

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 we visited all entries leave the loop unsuccessfully. */ | |

if (idx == first_idx) | |

break; | |

/* If entry is found use it. */ | |

if (htab->table[idx].used == hval | |

&& strcmp (item.key, htab->table[idx].entry.key) == 0) | |

{ | |

*retval = &htab->table[idx].entry; | |

return 1; | |

} | |

} | |

while (htab->table[idx].used); | |

} | |

/* An empty bucket has been found. */ | |

if (action == ENTER) | |

{ | |

/* If table is full and another entry should be entered return | |

with error. */ | |

if (htab->filled == htab->size) | |

{ | |

__set_errno (ENOMEM); | |

*retval = NULL; | |

return 0; | |

} | |

htab->table[idx].used = hval; | |

htab->table[idx].entry = item; | |

++htab->filled; | |

*retval = &htab->table[idx].entry; | |

return 1; | |

} | |

__set_errno (ESRCH); | |

*retval = NULL; | |

return 0; | |

} | |

libc_hidden_def (hsearch_r) |