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1/* $Header: malloc.c,v 1.0 87/12/18 13:05:35 root Exp $
2 *
3 * $Log: malloc.c,v $
4 * Revision 1.0 87/12/18 13:05:35 root
5 * Initial revision
6 *
7 */
8
9#ifndef lint
10static char sccsid[] = "@(#)malloc.c 4.3 (Berkeley) 9/16/83";
11#endif
12#include <stdio.h>
13
14#define RCHECK
15/*
16 * malloc.c (Caltech) 2/21/82
17 * Chris Kingsley, kingsley@cit-20.
18 *
19 * This is a very fast storage allocator. It allocates blocks of a small
20 * number of different sizes, and keeps free lists of each size. Blocks that
21 * don't exactly fit are passed up to the next larger size. In this
22 * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long.
23 * This is designed for use in a program that uses vast quantities of memory,
24 * but bombs when it runs out.
25 */
26
27#include <sys/types.h>
28
29#define NULL 0
30
31/*
32 * The overhead on a block is at least 4 bytes. When free, this space
33 * contains a pointer to the next free block, and the bottom two bits must
34 * be zero. When in use, the first byte is set to MAGIC, and the second
35 * byte is the size index. The remaining bytes are for alignment.
36 * If range checking is enabled and the size of the block fits
37 * in two bytes, then the top two bytes hold the size of the requested block
38 * plus the range checking words, and the header word MINUS ONE.
39 */
40union overhead {
41 union overhead *ov_next; /* when free */
42 struct {
43 u_char ovu_magic; /* magic number */
44 u_char ovu_index; /* bucket # */
45#ifdef RCHECK
46 u_short ovu_size; /* actual block size */
47 u_int ovu_rmagic; /* range magic number */
48#endif
49 } ovu;
50#define ov_magic ovu.ovu_magic
51#define ov_index ovu.ovu_index
52#define ov_size ovu.ovu_size
53#define ov_rmagic ovu.ovu_rmagic
54};
55
56#define MAGIC 0xff /* magic # on accounting info */
57#define RMAGIC 0x55555555 /* magic # on range info */
58#ifdef RCHECK
59#define RSLOP sizeof (u_int)
60#else
61#define RSLOP 0
62#endif
63
64/*
65 * nextf[i] is the pointer to the next free block of size 2^(i+3). The
66 * smallest allocatable block is 8 bytes. The overhead information
67 * precedes the data area returned to the user.
68 */
69#define NBUCKETS 30
70static union overhead *nextf[NBUCKETS];
71extern char *sbrk();
72
73#ifdef MSTATS
74/*
75 * nmalloc[i] is the difference between the number of mallocs and frees
76 * for a given block size.
77 */
78static u_int nmalloc[NBUCKETS];
79#include <stdio.h>
80#endif
81
82#ifdef debug
83#define ASSERT(p) if (!(p)) botch("p"); else
84static
85botch(s)
86 char *s;
87{
88
89 printf("assertion botched: %s\n", s);
90 abort();
91}
92#else
93#define ASSERT(p)
94#endif
95
96char *
97malloc(nbytes)
98 register unsigned nbytes;
99{
100 register union overhead *p;
101 register int bucket = 0;
102 register unsigned shiftr;
103
104 /*
105 * Convert amount of memory requested into
106 * closest block size stored in hash buckets
107 * which satisfies request. Account for
108 * space used per block for accounting.
109 */
110 nbytes += sizeof (union overhead) + RSLOP;
111 nbytes = (nbytes + 3) &~ 3;
112 shiftr = (nbytes - 1) >> 2;
113 /* apart from this loop, this is O(1) */
114 while (shiftr >>= 1)
115 bucket++;
116 /*
117 * If nothing in hash bucket right now,
118 * request more memory from the system.
119 */
120 if (nextf[bucket] == NULL)
121 morecore(bucket);
122 if ((p = (union overhead *)nextf[bucket]) == NULL)
123 return (NULL);
124 /* remove from linked list */
125 if (*((int*)p) > 0x10000000)
126 fprintf(stderr,"Corrupt malloc ptr 0x%x at 0x%x\n",*((int*)p),p);
127 nextf[bucket] = nextf[bucket]->ov_next;
128 p->ov_magic = MAGIC;
129 p->ov_index= bucket;
130#ifdef MSTATS
131 nmalloc[bucket]++;
132#endif
133#ifdef RCHECK
134 /*
135 * Record allocated size of block and
136 * bound space with magic numbers.
137 */
138 if (nbytes <= 0x10000)
139 p->ov_size = nbytes - 1;
140 p->ov_rmagic = RMAGIC;
141 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC;
142#endif
143 return ((char *)(p + 1));
144}
145
146/*
147 * Allocate more memory to the indicated bucket.
148 */
149static
150morecore(bucket)
151 register bucket;
152{
153 register union overhead *op;
154 register int rnu; /* 2^rnu bytes will be requested */
155 register int nblks; /* become nblks blocks of the desired size */
156 register int siz;
157
158 if (nextf[bucket])
159 return;
160 /*
161 * Insure memory is allocated
162 * on a page boundary. Should
163 * make getpageize call?
164 */
165 op = (union overhead *)sbrk(0);
166 if ((int)op & 0x3ff)
167 sbrk(1024 - ((int)op & 0x3ff));
168 /* take 2k unless the block is bigger than that */
169 rnu = (bucket <= 8) ? 11 : bucket + 3;
170 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */
171 if (rnu < bucket)
172 rnu = bucket;
173 op = (union overhead *)sbrk(1 << rnu);
174 /* no more room! */
175 if ((int)op == -1)
176 return;
177 /*
178 * Round up to minimum allocation size boundary
179 * and deduct from block count to reflect.
180 */
181 if ((int)op & 7) {
182 op = (union overhead *)(((int)op + 8) &~ 7);
183 nblks--;
184 }
185 /*
186 * Add new memory allocated to that on
187 * free list for this hash bucket.
188 */
189 nextf[bucket] = op;
190 siz = 1 << (bucket + 3);
191 while (--nblks > 0) {
192 op->ov_next = (union overhead *)((caddr_t)op + siz);
193 op = (union overhead *)((caddr_t)op + siz);
194 }
195}
196
197free(cp)
198 char *cp;
199{
200 register int size;
201 register union overhead *op;
202
203 if (cp == NULL)
204 return;
205 op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
206#ifdef debug
207 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */
208#else
209 if (op->ov_magic != MAGIC)
210 return; /* sanity */
211#endif
212#ifdef RCHECK
213 ASSERT(op->ov_rmagic == RMAGIC);
214 if (op->ov_index <= 13)
215 ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC);
216#endif
217 ASSERT(op->ov_index < NBUCKETS);
218 size = op->ov_index;
219 op->ov_next = nextf[size];
220 nextf[size] = op;
221#ifdef MSTATS
222 nmalloc[size]--;
223#endif
224}
225
226/*
227 * When a program attempts "storage compaction" as mentioned in the
228 * old malloc man page, it realloc's an already freed block. Usually
229 * this is the last block it freed; occasionally it might be farther
230 * back. We have to search all the free lists for the block in order
231 * to determine its bucket: 1st we make one pass thru the lists
232 * checking only the first block in each; if that fails we search
233 * ``realloc_srchlen'' blocks in each list for a match (the variable
234 * is extern so the caller can modify it). If that fails we just copy
235 * however many bytes was given to realloc() and hope it's not huge.
236 */
237int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */
238
239char *
240realloc(cp, nbytes)
241 char *cp;
242 unsigned nbytes;
243{
244 register u_int onb;
245 union overhead *op;
246 char *res;
247 register int i;
248 int was_alloced = 0;
249
250 if (cp == NULL)
251 return (malloc(nbytes));
252 op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
253 if (op->ov_magic == MAGIC) {
254 was_alloced++;
255 i = op->ov_index;
256 } else {
257 /*
258 * Already free, doing "compaction".
259 *
260 * Search for the old block of memory on the
261 * free list. First, check the most common
262 * case (last element free'd), then (this failing)
263 * the last ``realloc_srchlen'' items free'd.
264 * If all lookups fail, then assume the size of
265 * the memory block being realloc'd is the
266 * smallest possible.
267 */
268 if ((i = findbucket(op, 1)) < 0 &&
269 (i = findbucket(op, realloc_srchlen)) < 0)
270 i = 0;
271 }
272 onb = (1 << (i + 3)) - sizeof (*op) - RSLOP;
273 /* avoid the copy if same size block */
274 if (was_alloced &&
275 nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP)
276 return(cp);
277 if ((res = malloc(nbytes)) == NULL)
278 return (NULL);
279 if (cp != res) /* common optimization */
280 bcopy(cp, res, (nbytes < onb) ? nbytes : onb);
281 if (was_alloced)
282 free(cp);
283 return (res);
284}
285
286/*
287 * Search ``srchlen'' elements of each free list for a block whose
288 * header starts at ``freep''. If srchlen is -1 search the whole list.
289 * Return bucket number, or -1 if not found.
290 */
291static
292findbucket(freep, srchlen)
293 union overhead *freep;
294 int srchlen;
295{
296 register union overhead *p;
297 register int i, j;
298
299 for (i = 0; i < NBUCKETS; i++) {
300 j = 0;
301 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) {
302 if (p == freep)
303 return (i);
304 j++;
305 }
306 }
307 return (-1);
308}
309
310#ifdef MSTATS
311/*
312 * mstats - print out statistics about malloc
313 *
314 * Prints two lines of numbers, one showing the length of the free list
315 * for each size category, the second showing the number of mallocs -
316 * frees for each size category.
317 */
318mstats(s)
319 char *s;
320{
321 register int i, j;
322 register union overhead *p;
323 int totfree = 0,
324 totused = 0;
325
326 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s);
327 for (i = 0; i < NBUCKETS; i++) {
328 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++)
329 ;
330 fprintf(stderr, " %d", j);
331 totfree += j * (1 << (i + 3));
332 }
333 fprintf(stderr, "\nused:\t");
334 for (i = 0; i < NBUCKETS; i++) {
335 fprintf(stderr, " %d", nmalloc[i]);
336 totused += nmalloc[i] * (1 << (i + 3));
337 }
338 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n",
339 totused, totfree);
340}
341#endif