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Annotation of researchv10no/cmd/f77/alt/malloc.c, revision 1.1

1.1     ! root        1: #define ASSERT(p) if(!(p))botch("p");else
        !             2: botch(s)
        !             3: char *s;
        !             4: {
        !             5:        printf("assertion botched: %s\n",s);
        !             6:        abort();
        !             7: }
        !             8: /*     C storage allocator
        !             9:  *     circular first-fit strategy
        !            10:  *     works with noncontiguous, but monotonically linked, arena
        !            11:  *     each block is preceded by a ptr to the (pointer of) 
        !            12:  *     the next following block
        !            13:  *     blocks are exact number of words long; BUSY
        !            14:  *     bit in ptr is 1 for busy, 0 for idle
        !            15:  *     gaps in arena are merely noted as busy blocks
        !            16:  *     last block of arena (pointed to by alloct) is empty and
        !            17:  *     has a pointer to first
        !            18:  *     idle blocks are coalesced during space search
        !            19: */
        !            20: /*     all these defines must be powers of 2 */
        !            21: #define WORD sizeof(struct store)
        !            22: #define BLOCK 1024
        !            23: #define BUSY 1
        !            24: #define NULL 0
        !            25: #define testbusy(p) ((int)(p)&BUSY)
        !            26: #define setbusy(p) ((int)(p)+BUSY)
        !            27: #define clearbusy(p) ((int)(p)&~BUSY)
        !            28: 
        !            29: struct store { struct store *ptr; };
        !            30: 
        !            31: struct store allocs[] = {      /*initial arena*/
        !            32:        setbusy(&allocs[1].ptr),
        !            33:        setbusy(&allocs[0].ptr)
        !            34: };
        !            35: struct store *allocp = &allocs[1];     /*search ptr*/
        !            36: struct store *alloct = &allocs[1];     /*arena top*/
        !            37: struct store *allocx;          /*for benefit of realloc*/
        !            38: struct store *sbrk();
        !            39: 
        !            40: struct store *
        !            41: malloc(nbytes)
        !            42: unsigned nbytes;
        !            43: {
        !            44:        register struct store *p, *q;
        !            45:        register nw;
        !            46:        static temp;    /*coroutines assume no auto*/
        !            47: 
        !            48:        nw = (nbytes+2*WORD-1)/WORD;
        !            49:        ASSERT(allocp>allocs && allocp<=alloct);
        !            50:        for(p=allocp; ; ) {
        !            51:                for(temp=0; ; ) {
        !            52:                        if(!testbusy(p->ptr)) {
        !            53:                                while(!testbusy((q=p->ptr)->ptr)) {
        !            54:                                        ASSERT(q>p&&q<alloct);
        !            55:                                        p->ptr = q->ptr;
        !            56:                                }
        !            57:                                if(q>=p+nw && p+nw>=p)
        !            58:                                        goto found;
        !            59:                        }
        !            60:                        q = p;
        !            61:                        p = clearbusy(p->ptr);
        !            62:                        if(p>q)
        !            63:                                ASSERT(p<=alloct);
        !            64:                        else if(q!=alloct || p!=allocs) {
        !            65:                                write(2,"corrupt arena\n",14);
        !            66:                                exit(0175);
        !            67:                        } else if(++temp>1)
        !            68:                                break;
        !            69:                }
        !            70:                temp = (nw+BLOCK/WORD)&~(BLOCK/WORD-1);
        !            71:                q = sbrk(0);
        !            72:                if(q+temp < q)
        !            73:                        return(NULL);
        !            74:                q = sbrk(temp*WORD);
        !            75:                if((int)q == -1)
        !            76:                        return(NULL);
        !            77:                ASSERT(q>alloct);
        !            78:                alloct->ptr = q;
        !            79:                if(q!=alloct+1)
        !            80:                        alloct->ptr = setbusy(alloct->ptr);
        !            81:                alloct = q->ptr = q+temp-1;
        !            82:                alloct->ptr = setbusy(allocs);
        !            83:        }
        !            84: found:
        !            85:        allocp = p + nw;
        !            86:        ASSERT(allocp<=alloct);
        !            87:        if(q>allocp) {
        !            88:                allocx = allocp->ptr;
        !            89:                allocp->ptr = p->ptr;
        !            90:        }
        !            91:        p->ptr = setbusy(allocp);
        !            92:        return(p+1);
        !            93: }
        !            94: /*     freeing strategy tuned for LIFO allocation
        !            95: */
        !            96: free(p)
        !            97: register struct store *p;
        !            98: {
        !            99:        ASSERT(p>clearbusy(allocs[1].ptr)&&p<=alloct);
        !           100:        allocp = --p;
        !           101:        ASSERT(testbusy(p->ptr));
        !           102:        p->ptr = clearbusy(p->ptr);
        !           103:        ASSERT(p->ptr > allocp && p->ptr <= alloct);
        !           104: }
        !           105: 
        !           106: struct { unsigned tag:4, vtype:4;};
        !           107: 
        !           108: prbusy()
        !           109: {
        !           110:        register struct store *p, *q;
        !           111: 
        !           112:        ASSERT(allocp>allocs && allocp<=alloct);
        !           113:        for(p=allocs; ; ) {
        !           114:                        if(testbusy(p->ptr))
        !           115:                                {
        !           116:                                printf("busy 0%o, tag %d, type %d, length %d\n",
        !           117:                                        p, p[1].tag, p[1].vtype,
        !           118:                                        clearbusy(p->ptr) - (int) p - 2 );
        !           119:                                }
        !           120:                        q = p;
        !           121:                        p = clearbusy(p->ptr);
        !           122:                        if(p>q)
        !           123:                                ASSERT(p<=alloct);
        !           124:                        else if(q!=alloct || p!=allocs)
        !           125:                                {
        !           126:                                write(2,"corrupt arena\n",14);
        !           127:                                exit(0175);
        !           128:                                }
        !           129:                        else return;
        !           130:        }
        !           131: }

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