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Annotation of 40BSD/lib/libI77uc/dballoc.c, revision 1.1

1.1     ! root        1: /*     C storage allocator
        !             2:  *     circular first-fit strategy
        !             3:  *     works with noncontiguous, but monotonically linked, arena
        !             4:  *     each block is preceded by a ptr to the (pointer of) 
        !             5:  *     the next following block
        !             6:  *     blocks are exact number of words long; BUSY
        !             7:  *     bit in ptr is 1 for busy, 0 for idle
        !             8:  *     gaps in arena are merely noted as busy blocks
        !             9:  *     last block of arena (pointed to by alloct) is empty and
        !            10:  *     has a pointer to first
        !            11:  *     idle blocks are coalesced during space search
        !            12: */
        !            13: 
        !            14: #include       <stdio.h>
        !            15: 
        !            16: /*     all these defines must be powers of 2 */
        !            17: #define WORD sizeof(struct store)
        !            18: #define BLOCK 1024
        !            19: #define BUSY 1
        !            20: #define NULL 0
        !            21: #define testbusy(p) ((int)(p)&BUSY)
        !            22: #define setbusy(p) (struct store *)((int)(p)+BUSY)
        !            23: #define clearbusy(p) (struct store *)((int)(p)&~BUSY)
        !            24: 
        !            25: /*
        !            26: #define debug YES
        !            27: */
        !            28: 
        !            29: #ifndef debug
        !            30: #define ASSERT(p)
        !            31: #endif
        !            32: 
        !            33: #ifdef debug
        !            34: #define ASSERT(p) if(!(p))botch("p");else
        !            35: 
        !            36: botch(s) char *s;
        !            37: {
        !            38:        fatal(119,s);
        !            39: }
        !            40: #endif
        !            41: 
        !            42: struct store { struct store *ptr; };
        !            43: 
        !            44: struct store allocs[] = {      /*initial arena*/
        !            45:        setbusy(&allocs[1].ptr),
        !            46:        setbusy(&allocs[0].ptr)
        !            47: };
        !            48: struct store *allocp = &allocs[1];     /*search ptr*/
        !            49: struct store *alloct = &allocs[1];     /*arena top*/
        !            50: struct store *allocx = 0;              /*for benefit of realloc*/
        !            51: struct store *sbrk();
        !            52: 
        !            53: struct store *
        !            54: malloc(nbytes)
        !            55: unsigned nbytes;
        !            56: {
        !            57:        struct store *p, *q;
        !            58:        register nw;
        !            59:        static temp;    /*coroutines assume no auto*/
        !            60: 
        !            61: #ifdef verbose
        !            62:        printf("malloc(%d) ",nbytes);
        !            63: #endif
        !            64:        nw = (nbytes+2*WORD-1)/WORD;
        !            65:        ASSERT(allocp>allocs && allocp<=alloct);
        !            66:        for(p=allocp; ; ) {
        !            67:                for(temp=0; ; ) {
        !            68:                        if(!testbusy(p->ptr)) {
        !            69:                                while(!testbusy((q=p->ptr)->ptr)) {
        !            70:                                        ASSERT(q>p&&q<alloct);
        !            71:                                        p->ptr = q->ptr;
        !            72:                                }
        !            73:                                if(q>=p+nw && p+nw>=p)
        !            74:                                        goto found;
        !            75:                        }
        !            76:                        q = p;
        !            77:                        p = clearbusy(p->ptr);
        !            78:                        if(p>q)
        !            79:                                ASSERT(p<=alloct);
        !            80:                        else if(q!=alloct || p!=allocs) {
        !            81:                                fatal(119,"dballoc");
        !            82:                        } else if(++temp>1)
        !            83:                                break;
        !            84:                }
        !            85:                temp = (nw+BLOCK/WORD)&~(BLOCK/WORD-1);
        !            86:                q = sbrk(temp*WORD); /*SYSDEP*/
        !            87:                if((int)q == -1)
        !            88:                        return(NULL);
        !            89:                ASSERT(q>alloct);
        !            90:                alloct->ptr = q;
        !            91:                if(q!=alloct+1)
        !            92:                        alloct->ptr = setbusy(alloct->ptr);
        !            93:                alloct = q->ptr = q+temp-1;
        !            94:                alloct->ptr = setbusy(allocs);
        !            95:        }
        !            96: found:
        !            97:        allocp = p + nw;
        !            98:        ASSERT(allocp<=alloct);
        !            99:        if(q>allocp) {
        !           100:                allocx = allocp->ptr;
        !           101:                allocp->ptr = p->ptr;
        !           102:        }
        !           103:        p->ptr = setbusy(allocp);
        !           104: #ifdef verbose
        !           105:        printf("= %o\n",p+1);
        !           106: #endif
        !           107:        return(p+1);
        !           108: }
        !           109: 
        !           110: /*
        !           111:  *     freeing strategy tuned for LIFO allocation
        !           112:  */
        !           113: free(p)
        !           114: struct store *p;
        !           115: {
        !           116:        struct store *savep=p;
        !           117: #ifdef verbose
        !           118:        printf("free(%o)\n",p);
        !           119: #endif
        !           120:        ASSERT(p>clearbusy(allocs[1].ptr)&&p<=alloct);
        !           121:        allocp = --p;
        !           122:        ASSERT(testbusy(p->ptr));
        !           123:        p->ptr = clearbusy(p->ptr);
        !           124:        ASSERT(p->ptr > allocp && p->ptr <= alloct);
        !           125: }
        !           126: 
        !           127: char *calloc(nbytes,count)
        !           128: {      char *c;
        !           129:        c=(char *)malloc(nbytes*count);
        !           130:        return(c);
        !           131: }
        !           132: 
        !           133: struct store *
        !           134: realloc(p, nbytes)
        !           135: register struct store *p;
        !           136: unsigned nbytes;
        !           137: {
        !           138:        register struct store *q;
        !           139:        struct store *s, *t;
        !           140:        register unsigned nw;
        !           141:        unsigned onw;
        !           142: 
        !           143:        onw = p[-1].ptr - p;
        !           144:        q = malloc(nbytes);
        !           145:        if(q==NULL || q==p)
        !           146:                return(q);
        !           147:        s = p;
        !           148:        t = q;
        !           149:        nw = (nbytes+WORD-1)/WORD;
        !           150:        if(nw<onw)
        !           151:                onw = nw;
        !           152:        while(onw--!=0)
        !           153:                (t++)->ptr = (s++)->ptr;
        !           154:        if(q<p && q+nw>=p)
        !           155:                (q+(q+nw-p))->ptr = allocx;
        !           156:        return(q);
        !           157: }

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