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
  10: static 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:  */
  40: union   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
  70: static  union overhead *nextf[NBUCKETS];
  71: extern  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:  */
  78: static  u_int nmalloc[NBUCKETS];
  79: #include <stdio.h>
  80: #endif
  81: 
  82: #ifdef debug
  83: #define ASSERT(p)   if (!(p)) botch("p"); else
  84: static
  85: botch(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: 
  96: char *
  97: malloc(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:  */
 149: static
 150: morecore(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: 
 197: free(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:  */
 237: int realloc_srchlen = 4;    /* 4 should be plenty, -1 =>'s whole list */
 238: 
 239: char *
 240: realloc(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:  */
 291: static
 292: findbucket(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:  */
 318: mstats(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

Defined functions

botch defined in line 84; used 1 times
  • in line 83
findbucket defined in line 291; used 2 times
free defined in line 197; used 2 times
malloc defined in line 96; used 4 times
morecore defined in line 149; used 1 times
mstats defined in line 318; never used
realloc defined in line 239; used 2 times

Defined variables

nextf defined in line 70; used 10 times
nmalloc defined in line 78; used 4 times
realloc_srchlen defined in line 237; used 1 times
sccsid defined in line 10; never used

Defined union's

overhead defined in line 40; used 40 times

Defined macros

ASSERT defined in line 93; used 4 times
MAGIC defined in line 56; used 4 times
NBUCKETS defined in line 69; used 6 times
NULL defined in line 29; used 7 times
RCHECK defined in line 14; used 4 times
RMAGIC defined in line 57; used 4 times
RSLOP defined in line 61; used 5 times
ov_index defined in line 51; used 5 times
ov_magic defined in line 50; used 4 times
ov_rmagic defined in line 53; used 2 times
ov_size defined in line 52; used 2 times
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