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Change `-ise' to `-ize' throughout.
[mLib] / sub.c
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0875b58f 1/* -*-c-*-
2 *
8c6d948b 3 * $Id: sub.c,v 1.4 1999/05/13 22:48:55 mdw Exp $
0875b58f 4 *
5 * Allocation of known-size blocks
6 *
7 * (c) 1998 Straylight/Edgeware
8 */
9
c846879c 10/*----- Licensing notice --------------------------------------------------*
0875b58f 11 *
12 * This file is part of the mLib utilities library.
13 *
14 * mLib is free software; you can redistribute it and/or modify
c846879c 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 *
0875b58f 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
c846879c 22 * GNU Library General Public License for more details.
23 *
24 * You should have received a copy of the GNU Library General Public
0bd98442 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.
0875b58f 28 */
29
30/*----- Revision history --------------------------------------------------*
31 *
32 * $Log: sub.c,v $
8c6d948b 33 * Revision 1.4 1999/05/13 22:48:55 mdw
34 * Change `-ise' to `-ize' throughout.
35 *
0bd98442 36 * Revision 1.3 1999/05/06 19:51:35 mdw
37 * Reformatted the LGPL notice a little bit.
38 *
c846879c 39 * Revision 1.2 1999/05/05 18:50:31 mdw
40 * Change licensing conditions to LGPL.
41 *
42 * Revision 1.1.1.1 1998/06/17 23:44:42 mdw
43 * Initial version of mLib
0875b58f 44 *
45 */
46
47/*----- The big idea ------------------------------------------------------*
48 *
49 * This file provides an extra layer over @malloc@. It provides fast
8c6d948b 50 * turnover for small blocks, and tries to minimize the per-block overhead.
0875b58f 51 *
52 * To do its job, @alloc@ must place an extra restriction on you: you must
53 * know the size of a block when you free it. Usually you'll have this
54 * information encoded in some way either in the block or in the thing that
55 * referenced it, so this isn't a hardship.
56 *
57 * It works fairly simply. If a request for a big block (as defined by the
58 * constants below) comes in, it gets sent on to @malloc@ unmolested. For
59 * small blocks, it goes straight to a `bin' -- a list containing free blocks
60 * of exactly that size, or the nearest bigger size we can manage. If the
61 * bin is empty, a `chunk' is allocated from @malloc@: this has enough room
62 * for lots of blocks of the requested size, so it ets split up and each
63 * individual small block is added to the bin list. The first block in the
64 * bin list is then removed and given to the caller. In this way, @malloc@
65 * only stores its information once for lots of little blocks, so we save
66 * memory. Because I know where the correct bin is just from the block size,
67 * and I don't need to do any searching at all in the usual case (because the
68 * list isn't empty) I can get a speed advantage too.
69 *
70 * This code is almost certainly not ANSI conformant, although I'm not
71 * actually sure. If some kind soul would let me know how seriously I've
72 * violated the standard, and whether this is easily fixable, I'd be
73 * grateful.
74 */
75
76/*----- Header files ------------------------------------------------------*/
77
78/* --- ANSI headers --- */
79
80#include <stdio.h>
81#include <stdlib.h>
82#include <string.h>
83
84/* --- Local headers --- */
85
86#undef TRACK_ENABLE /* Can't track suballoc routines */
87#include "alloc.h"
88
89/*----- Configuration and tuning ------------------------------------------*/
90
91/* --- The largest block I'll handle here --- *
92 *
93 * Anything larger will be handed on to @malloc@.
94 */
95
96#define SUB_MAXBIN 256
97
98/* --- Preferred chunk size --- *
99 *
100 * When a bin is empty, I'll allocate a large chunk of approximately this
101 * size and divvy it up into small bin-sized blocks.
102 */
103
104#define SUB_CHUNK 4096
105
106/*----- Other useful macros -----------------------------------------------*/
107
108/* --- The granularity of bin buffers --- *
109 *
110 * All blocks allocated by the binner are a multiple of this size. I've
111 * chosen @void *@ because I need to store @void *@ things in here.
112 */
113
114#define SUB_GRANULE sizeof(void *)
115
116/* --- Finding the right bin for a given size --- *
117 *
118 * This chooses the correct bin for an allocation. Input is the size of
119 * block wanted; result is the bin index.
120 */
121
122#define SUB_BIN(x) (((x) + SUB_GRANULE - 1) / SUB_GRANULE)
123
124/* --- Convert a bin back to the block size --- *
125 *
126 * This gives the size of block contained in a given bin.
127 */
128
129#define SUB_BINSZ(x) ((x) * SUB_GRANULE)
130
131/* --- Number of bins required --- */
132
133#define SUB_BINS (SUB_MAXBIN / SUB_GRANULE + 1)
134
135/*----- Static variables --------------------------------------------------*/
136
137static void *sub__bins[SUB_BINS];
138static size_t sub__sizes[SUB_BINS];
139
140/*----- Main code ---------------------------------------------------------*/
141
142/* --- @sub_alloc@ --- *
143 *
144 * Arguments: @size_t s@ = size of chunk wanted
145 *
146 * Returns: Pointer to a block at least as large as the one wanted.
147 *
148 * Use: Allocates a small block of memory. If there is no more
149 * memory left, the exception @EXC_NOMEM@ is raised.
150 */
151
152void *sub_alloc(size_t s)
153{
154 int bin = SUB_BIN(s);
155 void *p;
156
157 /* --- Handle oversize blocks --- */
158
159 if (bin >= SUB_BINS)
160 return (xmalloc(s));
161
162 /* --- If the bin is empty, find some memory --- */
163
164 if (!sub__bins[bin]) {
165 char *p, *q;
166
167 p = xmalloc(sub__sizes[bin]);
168 q = p + sub__sizes[bin];
169
170 s = SUB_BINSZ(bin);
171
172 q -= s;
173 *(void **)q = 0;
174
175 while (q > p) {
176 q -= s;
177 *(void **)q = q + s;
178 }
179
180 sub__bins[bin] = p;
181 }
182
183 /* --- Extract the first block in the list --- */
184
185 p = sub__bins[bin];
186 sub__bins[bin] = *(void **)p;
187 return (p);
188}
189
190/* --- @sub_free@ --- *
191 *
192 * Arguments: @void *p@ = address of block to free
193 * @size_t s@ = size of block
194 *
195 * Returns: ---
196 *
197 * Use: Frees a block allocated by @sub_alloc@.
198 */
199
200void sub_free(void *p, size_t s)
201{
202 int bin = SUB_BIN(s);
203
204 if (bin >= SUB_BINS)
205 free(p);
206 else {
207 *(void **)p = sub__bins[bin];
208 sub__bins[bin] = p;
209 }
210}
211
212/* --- @sub_init@ --- *
213 *
214 * Arguments: ---
215 *
216 * Returns: ---
217 *
8c6d948b 218 * Use: Initializes the magic allocator.
0875b58f 219 */
220
221void sub_init(void)
222{
223 int i;
224
8c6d948b 225 /* --- Initialize the sizes bins --- */
0875b58f 226
227 for (i = 1; i < SUB_BINS; i++) {
228 sub__sizes[i] = ((SUB_CHUNK + SUB_BINSZ(i) - 1) /
229 SUB_BINSZ(i) * SUB_BINSZ(i));
230 }
231}
232
233/*----- Debugging code ----------------------------------------------------*/
234
235#ifdef TEST_RIG
236
237#define BLOCKS 1024
238#define SIZE_MAX 2048
239#define ITERATIONS 500000
240
241int main(void)
242{
243 static void *block[BLOCKS];
244 static size_t size[BLOCKS];
245 size_t allocced = 0;
246 int i;
247 long count;
248
249 sub_init();
250
251 for (count = 0; count < ITERATIONS; count++) {
252 i = rand() % BLOCKS;
253 if (block[i]) {
254 sub_free(block[i], size[i]);
255 block[i] = 0;
256 allocced -= size[i];
257 } else {
258 block[i] = sub_alloc(size[i] =
259 rand() % (SUB_MAXBIN - 128) + 128);
260 allocced += size[i];
261 memset(block[i], 0, size[i]); /* trample allocated storage */
262 }
263 }
264
265 return (0);
266}
267
268#endif
269
270/*----- That's all, folks -------------------------------------------------*/