2.9BSD - /usr/src/ucb/csh/malloc.c

   1: static  char *sccsid = "@(#)malloc.c 4.1 10/9/80";
   2: 
   3: #ifdef debug
   4: #define ASSERT(p) if(!(p))botch("p");else
   5: botch(s)
   6: char *s;
   7: {
   8:     printf("assertion botched: %s\n",s);
   9:     abort();
  10: }
  11: #else
  12: #define ASSERT(p)
  13: #endif
  14: 
  15: /*	avoid break bug */
  16: #ifdef pdp11
  17: #define GRANULE 64
  18: #else
  19: #define GRANULE 0
  20: #endif
  21: /*	C storage allocator
  22:  *	circular first-fit strategy
  23:  *	works with noncontiguous, but monotonically linked, arena
  24:  *	each block is preceded by a ptr to the (pointer of)
  25:  *	the next following block
  26:  *	blocks are exact number of words long
  27:  *	aligned to the data type requirements of ALIGN
  28:  *	pointers to blocks must have BUSY bit 0
  29:  *	bit in ptr is 1 for busy, 0 for idle
  30:  *	gaps in arena are merely noted as busy blocks
  31:  *	last block of arena (pointed to by alloct) is empty and
  32:  *	has a pointer to first
  33:  *	idle blocks are coalesced during space search
  34:  *
  35:  *	a different implementation may need to redefine
  36:  *	ALIGN, NALIGN, BLOCK, BUSY, INT
  37:  *	where INT is integer type to which a pointer can be cast
  38: */
  39: #define INT int
  40: #define ALIGN int
  41: #define NALIGN 1
  42: #define WORD sizeof(union store)
  43: #define BLOCK 1024  /* a multiple of WORD*/
  44: #define BUSY 1
  45: #define NULL 0
  46: #define testbusy(p) ((INT)(p)&BUSY)
  47: #define setbusy(p) (union store *)((INT)(p)|BUSY)
  48: #define clearbusy(p) (union store *)((INT)(p)&~BUSY)
  49: 
  50: union store { union store *ptr;
  51:           ALIGN dummy[NALIGN];
  52:           int calloc;   /*calloc clears an array of integers*/
  53: };
  54: 
  55: static  union store allocs[2];  /*initial arena*/
  56: static  union store *allocp;    /*search ptr*/
  57: static  union store *alloct;    /*arena top*/
  58: static  union store *allocx;    /*for benefit of realloc*/
  59: char    *sbrk();
  60: 
  61: char *
  62: malloc(nbytes)
  63: unsigned nbytes;
  64: {
  65:     register union store *p, *q;
  66:     register nw;
  67:     static temp;    /*coroutines assume no auto*/
  68: 
  69:     if(allocs[0].ptr==0) {  /*first time*/
  70:         allocs[0].ptr = setbusy(&allocs[1]);
  71:         allocs[1].ptr = setbusy(&allocs[0]);
  72:         alloct = &allocs[1];
  73:         allocp = &allocs[0];
  74:     }
  75:     nw = (nbytes+WORD+WORD-1)/WORD;
  76:     ASSERT(allocp>=allocs && allocp<=alloct);
  77:     ASSERT(allock());
  78:     for(p=allocp; ; ) {
  79:         for(temp=0; ; ) {
  80:             if(!testbusy(p->ptr)) {
  81:                 while(!testbusy((q=p->ptr)->ptr)) {
  82:                     ASSERT(q>p&&q<alloct);
  83:                     p->ptr = q->ptr;
  84:                 }
  85:                 if(q>=p+nw && p+nw>=p)
  86:                     goto found;
  87:             }
  88:             q = p;
  89:             p = clearbusy(p->ptr);
  90:             if(p>q)
  91:                 ASSERT(p<=alloct);
  92:             else if(q!=alloct || p!=allocs) {
  93:                 ASSERT(q==alloct&&p==allocs);
  94:                 return(NULL);
  95:             } else if(++temp>1)
  96:                 break;
  97:         }
  98:         temp = ((nw+BLOCK/WORD)/(BLOCK/WORD))*(BLOCK/WORD);
  99:         q = (union store *)sbrk(0);
 100:         if(q+temp+GRANULE < q) {
 101:             return(NULL);
 102:         }
 103:         q = (union store *)sbrk(temp*WORD);
 104:         if((INT)q == -1) {
 105:             return(NULL);
 106:         }
 107:         ASSERT(q>alloct);
 108:         alloct->ptr = q;
 109:         if(q!=alloct+1)
 110:             alloct->ptr = setbusy(alloct->ptr);
 111:         alloct = q->ptr = q+temp-1;
 112:         alloct->ptr = setbusy(allocs);
 113:     }
 114: found:
 115:     allocp = p + nw;
 116:     ASSERT(allocp<=alloct);
 117:     if(q>allocp) {
 118:         allocx = allocp->ptr;
 119:         allocp->ptr = p->ptr;
 120:     }
 121:     p->ptr = setbusy(allocp);
 122:     return((char *)(p+1));
 123: }
 124: 
 125: /*	freeing strategy tuned for LIFO allocation
 126: */
 127: free(ap)
 128: register char *ap;
 129: {
 130:     register union store *p = (union store *)ap;
 131: 
 132:     ASSERT(p>clearbusy(allocs[1].ptr)&&p<=alloct);
 133:     ASSERT(allock());
 134:     allocp = --p;
 135:     ASSERT(testbusy(p->ptr));
 136:     p->ptr = clearbusy(p->ptr);
 137:     ASSERT(p->ptr > allocp && p->ptr <= alloct);
 138: }
 139: 
 140: /*	realloc(p, nbytes) reallocates a block obtained from malloc()
 141:  *	and freed since last call of malloc()
 142:  *	to have new size nbytes, and old content
 143:  *	returns new location, or 0 on failure
 144: */
 145: 
 146: char *
 147: realloc(p, nbytes)
 148: register union store *p;
 149: unsigned nbytes;
 150: {
 151:     register union store *q;
 152:     union store *s, *t;
 153:     register unsigned nw;
 154:     unsigned onw;
 155: 
 156:     if(testbusy(p[-1].ptr))
 157:         free((char *)p);
 158:     onw = p[-1].ptr - p;
 159:     q = (union store *)malloc(nbytes);
 160:     if(q==NULL || q==p)
 161:         return((char *)q);
 162:     s = p;
 163:     t = q;
 164:     nw = (nbytes+WORD-1)/WORD;
 165:     if(nw<onw)
 166:         onw = nw;
 167:     while(onw--!=0)
 168:         *t++ = *s++;
 169:     if(q<p && q+nw>=p)
 170:         (q+(q+nw-p))->ptr = allocx;
 171:     return((char *)q);
 172: }
 173: 
 174: #ifdef debug
 175: allock()
 176: {
 177: #ifdef longdebug
 178:     register union store *p;
 179:     int x;
 180:     x = 0;
 181:     for(p= &allocs[0]; clearbusy(p->ptr) > p; p=clearbusy(p->ptr)) {
 182:         if(p==allocp)
 183:             x++;
 184:     }
 185:     ASSERT(p==alloct);
 186:     return(x==1|p==allocp);
 187: #else
 188:     return(1);
 189: #endif
 190: }
 191: #endif

Defined functions

Defined variables

Defined union's

Defined macros