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Annotation of 41BSD/libc/gen/malloc.c, revision 1.1

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

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