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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: sub.c,v 1.7 2003/05/18 15:10:20 mdw Exp $ |
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4 | * |
5 | * Allocation of known-size blocks |
6 | * |
7 | * (c) 1998 Straylight/Edgeware |
8 | */ |
9 | |
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10 | /*----- Licensing notice --------------------------------------------------* |
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11 | * |
12 | * This file is part of the mLib utilities library. |
13 | * |
14 | * mLib is free software; you can redistribute it and/or modify |
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15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
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19 | * mLib is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
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25 | * License along with mLib; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
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28 | */ |
29 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: sub.c,v $ |
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33 | * Revision 1.7 2003/05/18 15:10:20 mdw |
34 | * Add debugging mode which just uses the underlying arena. |
35 | * |
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36 | * Revision 1.6 2000/06/17 10:35:51 mdw |
37 | * Major overhaul for arena support. |
38 | * |
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39 | * Revision 1.5 1999/05/19 20:27:11 mdw |
40 | * Change naming to match newer mLib conventions. |
41 | * |
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42 | * Revision 1.4 1999/05/13 22:48:55 mdw |
43 | * Change `-ise' to `-ize' throughout. |
44 | * |
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45 | * Revision 1.3 1999/05/06 19:51:35 mdw |
46 | * Reformatted the LGPL notice a little bit. |
47 | * |
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48 | * Revision 1.2 1999/05/05 18:50:31 mdw |
49 | * Change licensing conditions to LGPL. |
50 | * |
51 | * Revision 1.1.1.1 1998/06/17 23:44:42 mdw |
52 | * Initial version of mLib |
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53 | * |
54 | */ |
55 | |
56 | /*----- The big idea ------------------------------------------------------* |
57 | * |
58 | * This file provides an extra layer over @malloc@. It provides fast |
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59 | * turnover for small blocks, and tries to minimize the per-block overhead. |
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60 | * |
61 | * To do its job, @alloc@ must place an extra restriction on you: you must |
62 | * know the size of a block when you free it. Usually you'll have this |
63 | * information encoded in some way either in the block or in the thing that |
64 | * referenced it, so this isn't a hardship. |
65 | * |
66 | * It works fairly simply. If a request for a big block (as defined by the |
67 | * constants below) comes in, it gets sent on to @malloc@ unmolested. For |
68 | * small blocks, it goes straight to a `bin' -- a list containing free blocks |
69 | * of exactly that size, or the nearest bigger size we can manage. If the |
70 | * bin is empty, a `chunk' is allocated from @malloc@: this has enough room |
71 | * for lots of blocks of the requested size, so it ets split up and each |
72 | * individual small block is added to the bin list. The first block in the |
73 | * bin list is then removed and given to the caller. In this way, @malloc@ |
74 | * only stores its information once for lots of little blocks, so we save |
75 | * memory. Because I know where the correct bin is just from the block size, |
76 | * and I don't need to do any searching at all in the usual case (because the |
77 | * list isn't empty) I can get a speed advantage too. |
78 | * |
79 | * This code is almost certainly not ANSI conformant, although I'm not |
80 | * actually sure. If some kind soul would let me know how seriously I've |
81 | * violated the standard, and whether this is easily fixable, I'd be |
82 | * grateful. |
83 | */ |
84 | |
85 | /*----- Header files ------------------------------------------------------*/ |
86 | |
87 | /* --- ANSI headers --- */ |
88 | |
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89 | #include <assert.h> |
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90 | #include <stdio.h> |
91 | #include <stdlib.h> |
92 | #include <string.h> |
93 | |
94 | /* --- Local headers --- */ |
95 | |
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96 | #include "arena.h" |
97 | #include "exc.h" |
98 | #include "sub.h" |
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99 | |
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100 | /*----- Configuration tweaks ----------------------------------------------*/ |
101 | |
102 | /* #define SUBARENA_TRIVIAL */ |
103 | |
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104 | /*----- Static variables --------------------------------------------------*/ |
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105 | |
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106 | static size_t sizes[SUB_BINS]; |
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107 | |
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108 | /*----- Global variables --------------------------------------------------*/ |
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109 | |
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110 | subarena sub_global; |
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111 | |
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112 | #ifdef SUBARENA_TRIVIAL |
113 | |
114 | typedef struct sub_link { |
115 | struct sub_link *next; |
116 | void *p; |
117 | size_t sz; |
118 | } sub_link; |
119 | |
120 | #endif |
121 | |
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122 | /*----- Main code ---------------------------------------------------------*/ |
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123 | |
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124 | /* --- @subarena_create@ --- * |
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125 | * |
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126 | * Arguments: @subarena *s@ = pointer to arena to initialize |
127 | * @arena *a@ = pointer to underlying arena block |
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128 | * |
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129 | * Returns: --- |
130 | * |
131 | * Use: Initialize a suballocation arena based on an underlying large |
132 | * blocks arena. |
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133 | */ |
134 | |
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135 | void subarena_create(subarena *s, arena *a) |
136 | { |
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137 | #ifdef SUBARENA_TRIVIAL |
138 | s->bin[0] = 0; |
139 | #else |
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140 | size_t i; |
141 | if (!sizes[1]) |
142 | sub_init(); |
143 | for (i = 0; i < SUB_BINS; i++) |
144 | s->bin[i] = 0; |
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145 | #endif |
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146 | s->a = a; |
147 | } |
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148 | |
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149 | /* --- @subarena_destroy@ --- * |
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150 | * |
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151 | * Arguments: @subarena *s@ = pointer to arena to destroy |
152 | * |
153 | * Returns: --- |
154 | * |
155 | * Use: Destroys a suballocation arena, freeing all of the memory it |
156 | * contains back to the underlying large blocks arena. |
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157 | */ |
158 | |
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159 | void subarena_destroy(subarena *s) |
160 | { |
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161 | #ifdef SUBARENA_TRIVIAL |
162 | |
163 | sub_link *l, *ll; |
164 | |
165 | for (l = s->bin[0]; l; l = ll) { |
166 | ll = l; |
167 | a_free(s->a, l->p); |
168 | a_free(s->a, l); |
169 | } |
170 | s->bin[0] = 0; |
171 | |
172 | #else |
173 | |
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174 | size_t i; |
175 | for (i = 0; i < SUB_BINS; i++) { |
176 | void *p = s->bin[i]; |
177 | while (p) { |
178 | void *q = p; |
179 | p = *(void **)q; |
180 | A_FREE(s->a, q); |
181 | } |
182 | } |
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183 | |
184 | #endif |
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185 | } |
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186 | |
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187 | /* --- @subarena_alloc@ --- * |
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188 | * |
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189 | * Arguments: @subarena *s@ = pointer to arena |
190 | * @size_t s@ = size of chunk wanted |
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191 | * |
192 | * Returns: Pointer to a block at least as large as the one wanted. |
193 | * |
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194 | * Use: Allocates a small block of memory from the given pool. The |
195 | * exception @EXC_NOMEM@ is raised if the underlying arena is |
196 | * full. |
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197 | */ |
198 | |
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199 | void *subarena_alloc(subarena *s, size_t sz) |
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200 | { |
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201 | #ifdef SUBARENA_TRIVIAL |
202 | |
203 | sub_link *l; |
204 | void *p; |
205 | |
206 | if (!s->a) |
207 | subarena_create(s, arena_global); |
208 | |
209 | if ((l = a_alloc(s->a, sizeof(*l))) == 0) |
210 | return (0); |
211 | if ((p = a_alloc(s->a, sz)) == 0) { |
212 | a_free(s->a, l); |
213 | return (0); |
214 | } |
215 | l->p = p; |
216 | l->sz = sz; |
217 | l->next = s->bin[0]; |
218 | s->bin[0] = l; |
219 | return (p); |
220 | |
221 | #else |
222 | |
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223 | int bin; |
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224 | void *p; |
225 | |
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226 | /* --- Ensure that everything is initialized --- */ |
227 | |
228 | if (!s->a) |
229 | subarena_create(s, arena_global); |
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230 | |
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231 | /* --- Handle oversize blocks --- */ |
232 | |
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233 | bin = SUB_BIN(sz); |
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234 | if (bin >= SUB_BINS) { |
235 | void *p = A_ALLOC(s->a, sz); |
236 | if (!p) |
237 | THROW(EXC_NOMEM); |
238 | return (p); |
239 | } |
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240 | |
241 | /* --- If the bin is empty, find some memory --- */ |
242 | |
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243 | if (!s->bin[bin]) { |
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244 | char *p, *q; |
245 | |
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246 | p = A_ALLOC(s->a, sizes[bin]); |
247 | if (!p) |
248 | THROW(EXC_NOMEM); |
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249 | q = p + sizes[bin]; |
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250 | |
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251 | sz = SUB_BINSZ(bin); |
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252 | |
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253 | q -= sz; |
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254 | *(void **)q = 0; |
255 | |
256 | while (q > p) { |
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257 | q -= sz; |
258 | *(void **)q = q + sz; |
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259 | } |
260 | |
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261 | s->bin[bin] = p; |
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262 | } |
263 | |
264 | /* --- Extract the first block in the list --- */ |
265 | |
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266 | p = s->bin[bin]; |
267 | s->bin[bin] = *(void **)p; |
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268 | return (p); |
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269 | |
270 | #endif |
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271 | } |
272 | |
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273 | /* --- @subarena_free@ --- * |
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274 | * |
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275 | * Arguments: @subarena *s@ = pointer to arena |
276 | * @void *p@ = address of block to free |
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277 | * @size_t s@ = size of block |
278 | * |
279 | * Returns: --- |
280 | * |
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281 | * Use: Frees a block allocated by @subarena_alloc@. |
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282 | */ |
283 | |
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284 | void subarena_free(subarena *s, void *p, size_t sz) |
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285 | { |
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286 | #ifdef SUBARENA_TRIVIAL |
287 | |
288 | sub_link *lh = s->bin[0], **l, *ll; |
289 | |
290 | for (l = &lh; *l && (*l)->p != p; l = &(*l)->next) |
291 | ; |
292 | ll = *l; |
293 | assert(ll); |
294 | assert(ll->sz == sz); |
295 | *l = ll->next; |
296 | a_free(s->a, ll); |
297 | a_free(s->a, p); |
298 | s->bin[0] = lh; |
299 | |
300 | #else |
301 | |
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302 | int bin = SUB_BIN(sz); |
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303 | |
304 | if (bin >= SUB_BINS) |
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305 | A_FREE(s->a, p); |
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306 | else { |
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307 | *(void **)p = s->bin[bin]; |
308 | s->bin[bin] = p; |
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309 | } |
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310 | |
311 | #endif |
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312 | } |
313 | |
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314 | /*----- Compatibility stuff -----------------------------------------------*/ |
315 | |
316 | /* --- @sub_alloc@ --- * |
317 | * |
318 | * Arguments: @size_t s@ = size of chunk wanted |
319 | * |
320 | * Returns: Pointer to a block at least as large as the one wanted. |
321 | * |
322 | * Use: Allocates a small block of memory from the @sub_global@ pool. |
323 | */ |
324 | |
325 | void *(sub_alloc)(size_t sz) { return sub_alloc(sz); } |
326 | |
327 | /* --- @sub_free@ --- * |
328 | * |
329 | * Arguments: @void *p@ = address of block to free |
330 | * @size_t s@ = size of block |
331 | * |
332 | * Returns: --- |
333 | * |
334 | * Use: Frees a block allocated by @sub_alloc@. |
335 | */ |
336 | |
337 | void (sub_free)(void *p, size_t sz) { sub_free(p, sz); } |
338 | |
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339 | /* --- @sub_init@ --- * |
340 | * |
341 | * Arguments: --- |
342 | * |
343 | * Returns: --- |
344 | * |
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345 | * Use: Initializes the magic allocator. |
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346 | */ |
347 | |
348 | void sub_init(void) |
349 | { |
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350 | #ifndef SUBARENA_TRIVIAL |
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351 | int i; |
352 | |
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353 | /* --- Initialize the sizes bins --- */ |
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354 | |
355 | for (i = 1; i < SUB_BINS; i++) { |
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356 | sizes[i] = ((SUB_CHUNK + SUB_BINSZ(i) - 1) / |
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357 | SUB_BINSZ(i) * SUB_BINSZ(i)); |
358 | } |
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359 | #endif |
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360 | } |
361 | |
362 | /*----- Debugging code ----------------------------------------------------*/ |
363 | |
364 | #ifdef TEST_RIG |
365 | |
366 | #define BLOCKS 1024 |
367 | #define SIZE_MAX 2048 |
368 | #define ITERATIONS 500000 |
369 | |
370 | int main(void) |
371 | { |
372 | static void *block[BLOCKS]; |
373 | static size_t size[BLOCKS]; |
374 | size_t allocced = 0; |
375 | int i; |
376 | long count; |
377 | |
378 | sub_init(); |
379 | |
380 | for (count = 0; count < ITERATIONS; count++) { |
381 | i = rand() % BLOCKS; |
382 | if (block[i]) { |
383 | sub_free(block[i], size[i]); |
384 | block[i] = 0; |
385 | allocced -= size[i]; |
386 | } else { |
387 | block[i] = sub_alloc(size[i] = |
388 | rand() % (SUB_MAXBIN - 128) + 128); |
389 | allocced += size[i]; |
390 | memset(block[i], 0, size[i]); /* trample allocated storage */ |
391 | } |
392 | } |
393 | |
394 | return (0); |
395 | } |
396 | |
397 | #endif |
398 | |
399 | /*----- That's all, folks -------------------------------------------------*/ |