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32db469edf
The number of buckets is calculated by performing a binary AND against
the mask of the hash table, which is one less than its size (which is a
power of two). This leads to all top bits being discarded, requiring
for short or similar inputs a hash function with a good avalanche
effect.
Use djb2a:
# current
common prefixes: 7 entries and 5/8 buckets used, longest chain
length 2, sum of chain length^2 11
classes: 134 entries and 100/256 buckets used, longest chain
length 5, sum of chain length^2 234
roles: 15 entries and 6/16 buckets used, longest chain length 5,
sum of chain length^2 57
types: 4448 entries and 3016/8192 buckets used, longest chain
length 41, sum of chain length^2 14922
users: 7 entries and 3/8 buckets used, longest chain length 3,
sum of chain length^2 17
bools: 306 entries and 221/512 buckets used, longest chain
length 4, sum of chain length^2 524
levels: 1 entries and 1/1 buckets used, longest chain length 1,
sum of chain length^2 1
categories: 1024 entries and 400/1024 buckets used, longest chain
length 4, sum of chain length^2 2740
# patch
common prefixes: 7 entries and 5/8 buckets used, longest chain
length 2, sum of chain length^2 11
classes: 134 entries and 101/256 buckets used, longest chain
length 3, sum of chain length^2 210
roles: 15 entries and 9/16 buckets used, longest chain length 3,
sum of chain length^2 31
types: 4448 entries and 3459/8192 buckets used, longest chain
length 5, sum of chain length^2 6778
users: 7 entries and 5/8 buckets used, longest chain length 3,
sum of chain length^2 13
bools: 306 entries and 236/512 buckets used, longest chain
length 5, sum of chain length^2 470
levels: 1 entries and 1/1 buckets used, longest chain length 1,
sum of chain length^2 1
categories: 1024 entries and 518/1024 buckets used, longest chain
length 7, sum of chain length^2 2992
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
[PM: line length fixes in the commit message]
Signed-off-by: Paul Moore <paul@paul-moore.com>
57 lines
1.1 KiB
C
57 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Implementation of the symbol table type.
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*
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* Author : Stephen Smalley, <stephen.smalley.work@gmail.com>
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*/
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#include <linux/kernel.h>
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#include <linux/string.h>
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#include <linux/errno.h>
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#include "symtab.h"
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static unsigned int symhash(const void *key)
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{
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/*
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* djb2a
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* Public domain from cdb v0.75
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*/
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unsigned int hash = 5381;
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unsigned char c;
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while ((c = *(const unsigned char *)key++))
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hash = ((hash << 5) + hash) ^ c;
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return hash;
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}
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static int symcmp(const void *key1, const void *key2)
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{
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const char *keyp1, *keyp2;
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keyp1 = key1;
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keyp2 = key2;
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return strcmp(keyp1, keyp2);
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}
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static const struct hashtab_key_params symtab_key_params = {
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.hash = symhash,
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.cmp = symcmp,
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};
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int symtab_init(struct symtab *s, u32 size)
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{
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s->nprim = 0;
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return hashtab_init(&s->table, size);
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}
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int symtab_insert(struct symtab *s, char *name, void *datum)
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{
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return hashtab_insert(&s->table, name, datum, symtab_key_params);
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}
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void *symtab_search(struct symtab *s, const char *name)
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{
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return hashtab_search(&s->table, name, symtab_key_params);
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}
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