| 1 | /* |
| 2 | * Copyright (c) 1992 The Regents of the University of California. |
| 3 | * All rights reserved. |
| 4 | * |
| 5 | * This software was developed by the Computer Systems Engineering group |
| 6 | * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and |
| 7 | * contributed to Berkeley. |
| 8 | * |
| 9 | * All advertising materials mentioning features or use of this software |
| 10 | * must display the following acknowledgement: |
| 11 | * This product includes software developed by the University of |
| 12 | * California, Lawrence Berkeley Laboratories. |
| 13 | * |
| 14 | * %sccs.include.redist.c% |
| 15 | * |
| 16 | * @(#)hash.c 5.2 (Berkeley) %G% |
| 17 | */ |
| 18 | |
| 19 | #include <sys/param.h> |
| 20 | #include <stdlib.h> |
| 21 | #include <string.h> |
| 22 | #include "config.h" |
| 23 | |
| 24 | /* |
| 25 | * Interned strings are kept in a hash table. By making each string |
| 26 | * unique, the program can compare strings by comparing pointers. |
| 27 | */ |
| 28 | struct hashent { |
| 29 | struct hashent *h_next; /* hash buckets are chained */ |
| 30 | const char *h_name; /* the string */ |
| 31 | u_int h_hash; /* its hash value */ |
| 32 | void *h_value; /* other values (for name=value) */ |
| 33 | }; |
| 34 | struct hashtab { |
| 35 | size_t ht_size; /* size (power of 2) */ |
| 36 | u_int ht_mask; /* == ht_size - 1 */ |
| 37 | u_int ht_used; /* number of entries used */ |
| 38 | u_int ht_lim; /* when to expand */ |
| 39 | struct hashent **ht_tab; /* base of table */ |
| 40 | }; |
| 41 | static struct hashtab strings; |
| 42 | |
| 43 | /* |
| 44 | * HASHFRACTION controls ht_lim, which in turn controls the average chain |
| 45 | * length. We allow a few entries, on average, as comparing them is usually |
| 46 | * cheap (the h_hash values prevent a strcmp). |
| 47 | */ |
| 48 | #define HASHFRACTION(sz) ((sz) * 3 / 2) |
| 49 | |
| 50 | /* round up to next multiple of y, where y is a power of 2 */ |
| 51 | #define ROUND(x, y) (((x) + (y) - 1) & ~((y) - 1)) |
| 52 | |
| 53 | /* |
| 54 | * Allocate space that will never be freed. |
| 55 | */ |
| 56 | static void * |
| 57 | poolalloc(size) |
| 58 | size_t size; |
| 59 | { |
| 60 | register char *p; |
| 61 | register size_t alloc; |
| 62 | static char *pool; |
| 63 | static size_t nleft; |
| 64 | |
| 65 | if (nleft < size) { |
| 66 | /* |
| 67 | * Compute a `good' size to allocate via malloc. |
| 68 | * 16384 is a guess at a good page size for malloc; |
| 69 | * 32 is a guess at malloc's overhead. |
| 70 | */ |
| 71 | alloc = ROUND(size + 32, 16384) - 32; |
| 72 | p = emalloc(alloc); |
| 73 | nleft = alloc - size; |
| 74 | } else { |
| 75 | p = pool; |
| 76 | nleft -= size; |
| 77 | } |
| 78 | pool = p + size; |
| 79 | return (p); |
| 80 | } |
| 81 | |
| 82 | /* |
| 83 | * Initialize a new hash table. The size must be a power of 2. |
| 84 | */ |
| 85 | static void |
| 86 | ht_init(ht, sz) |
| 87 | register struct hashtab *ht; |
| 88 | size_t sz; |
| 89 | { |
| 90 | register struct hashent **h; |
| 91 | register u_int n; |
| 92 | |
| 93 | h = emalloc(sz * sizeof *h); |
| 94 | ht->ht_tab = h; |
| 95 | ht->ht_size = sz; |
| 96 | ht->ht_mask = sz - 1; |
| 97 | for (n = 0; n < sz; n++) |
| 98 | *h++ = NULL; |
| 99 | ht->ht_used = 0; |
| 100 | ht->ht_lim = HASHFRACTION(sz); |
| 101 | } |
| 102 | |
| 103 | /* |
| 104 | * Expand an existing hash table. |
| 105 | */ |
| 106 | static void |
| 107 | ht_expand(ht) |
| 108 | register struct hashtab *ht; |
| 109 | { |
| 110 | register struct hashent *p, **h, **oldh, *q; |
| 111 | register u_int n, i; |
| 112 | |
| 113 | n = ht->ht_size * 2; |
| 114 | h = emalloc(n * sizeof *h); |
| 115 | for (i = 0; i < n; i++) |
| 116 | h[i] = NULL; |
| 117 | oldh = ht->ht_tab; |
| 118 | n--; |
| 119 | for (i = ht->ht_size; i != 0; i--) { |
| 120 | for (p = *oldh++; p != NULL; p = q) { |
| 121 | q = p->h_next; |
| 122 | p->h_next = h[p->h_hash & n]; |
| 123 | h[p->h_hash & n] = p; |
| 124 | } |
| 125 | } |
| 126 | free(ht->ht_tab); |
| 127 | ht->ht_tab = h; |
| 128 | ht->ht_mask = n; |
| 129 | ht->ht_size = ++n; |
| 130 | ht->ht_lim = HASHFRACTION(n); |
| 131 | } |
| 132 | |
| 133 | /* |
| 134 | * Make a new hash entry, setting its h_next to NULL. |
| 135 | */ |
| 136 | static inline struct hashent * |
| 137 | newhashent(name, h) |
| 138 | const char *name; |
| 139 | u_int h; |
| 140 | { |
| 141 | register struct hashent *hp; |
| 142 | register char *m; |
| 143 | |
| 144 | m = poolalloc(sizeof(*hp) + ALIGNBYTES); |
| 145 | hp = (struct hashent *)ALIGN(m); |
| 146 | hp->h_name = name; |
| 147 | hp->h_hash = h; |
| 148 | hp->h_next = NULL; |
| 149 | return (hp); |
| 150 | } |
| 151 | |
| 152 | /* |
| 153 | * Hash a string. |
| 154 | */ |
| 155 | static inline u_int |
| 156 | hash(str) |
| 157 | register const char *str; |
| 158 | { |
| 159 | register u_int h; |
| 160 | |
| 161 | for (h = 0; *str;) |
| 162 | h = (h << 5) + h + *str++; |
| 163 | return (h); |
| 164 | } |
| 165 | |
| 166 | void |
| 167 | initintern() |
| 168 | { |
| 169 | |
| 170 | ht_init(&strings, 128); |
| 171 | } |
| 172 | |
| 173 | /* |
| 174 | * Generate a single unique copy of the given string. We expect this |
| 175 | * function to be used frequently, so it should be fast. |
| 176 | */ |
| 177 | const char * |
| 178 | intern(s) |
| 179 | register const char *s; |
| 180 | { |
| 181 | register struct hashtab *ht; |
| 182 | register struct hashent *hp, **hpp; |
| 183 | register u_int h; |
| 184 | register char *p; |
| 185 | register size_t l; |
| 186 | |
| 187 | ht = &strings; |
| 188 | h = hash(s); |
| 189 | hpp = &ht->ht_tab[h & ht->ht_mask]; |
| 190 | for (; (hp = *hpp) != NULL; hpp = &hp->h_next) |
| 191 | if (hp->h_hash == h && strcmp(hp->h_name, s) == 0) |
| 192 | return (hp->h_name); |
| 193 | l = strlen(s) + 1; |
| 194 | p = poolalloc(l); |
| 195 | bcopy(s, p, l); |
| 196 | *hpp = newhashent(p, h); |
| 197 | if (++ht->ht_used > ht->ht_lim) |
| 198 | ht_expand(ht); |
| 199 | return (p); |
| 200 | } |
| 201 | |
| 202 | struct hashtab * |
| 203 | ht_new() |
| 204 | { |
| 205 | register struct hashtab *ht; |
| 206 | |
| 207 | ht = emalloc(sizeof *ht); |
| 208 | ht_init(ht, 8); |
| 209 | return (ht); |
| 210 | } |
| 211 | |
| 212 | /* |
| 213 | * Insert and/or replace. |
| 214 | */ |
| 215 | int |
| 216 | ht_insrep(ht, nam, val, replace) |
| 217 | register struct hashtab *ht; |
| 218 | register const char *nam; |
| 219 | void *val; |
| 220 | int replace; |
| 221 | { |
| 222 | register struct hashent *hp, **hpp; |
| 223 | register u_int h; |
| 224 | |
| 225 | h = hash(nam); |
| 226 | hpp = &ht->ht_tab[h & ht->ht_mask]; |
| 227 | for (; (hp = *hpp) != NULL; hpp = &hp->h_next) { |
| 228 | if (hp->h_name == nam) { |
| 229 | if (replace) |
| 230 | hp->h_value = val; |
| 231 | return (1); |
| 232 | } |
| 233 | } |
| 234 | *hpp = hp = newhashent(nam, h); |
| 235 | hp->h_value = val; |
| 236 | return (0); |
| 237 | } |
| 238 | |
| 239 | void * |
| 240 | ht_lookup(ht, nam) |
| 241 | register struct hashtab *ht; |
| 242 | register const char *nam; |
| 243 | { |
| 244 | register struct hashent *hp, **hpp; |
| 245 | register u_int h; |
| 246 | |
| 247 | h = hash(nam); |
| 248 | hpp = &ht->ht_tab[h & ht->ht_mask]; |
| 249 | for (; (hp = *hpp) != NULL; hpp = &hp->h_next) |
| 250 | if (hp->h_name == nam) |
| 251 | return (hp->h_value); |
| 252 | return (NULL); |
| 253 | } |