new malloc.c, derived from new Minix version
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ceriel
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30208cda9a
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@ -1,116 +1,185 @@
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/* $Header$ */
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/* replace undef by define */
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#undef DEBUG /* check assertions */
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#undef SLOWDEBUG /* some extra test loops (requires DEBUG) */
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#define CLICK_SIZE 4096
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#if EM_WSIZE == EM_PSIZE
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typedef unsigned int vir_bytes;
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#ifdef DEBUG
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#define ASSERT(b) if (!(b)) assert_failed();
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#else
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typedef long vir_bytes;
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#define ASSERT(b) /* empty */
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#endif
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extern bcopy();
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#define ALIGN(x, a) (((x) + (a - 1)) & ~(a - 1))
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#define BUSY 1
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#define NEXT(p) (* (char **) (p))
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#ifdef pdp
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#define BUGFIX 64 /* cannot set break in top 64 bytes */
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#ifdef EM_WSIZE == EM_PSIZE
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#define ptrint int
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#else
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#define BUGFIX 0
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#define ptrint long
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#endif
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#define BRKSIZE 4096
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#define PTRSIZE sizeof(char *)
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#define Align(x,a) (((x) + (a - 1)) & ~(a - 1))
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#define NextSlot(p) (* (char **) ((p) - PTRSIZE))
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#define NextFree(p) (* (char **) (p))
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/*
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* A short explanation of the data structure and algorithms.
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* An area returned by malloc() is called a slot. Each slot
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* contains the number of bytes requested, but preceeded by
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* an extra pointer to the next the slot in memory.
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* '_bottom' and '_top' point to the first/last slot.
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* More memory is asked for using brk() and appended to top.
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* The list of free slots is maintained to keep malloc() fast.
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* '_empty' points the the first free slot. Free slots are
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* linked together by a pointer at the start of the
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* user visable part, so just after the next-slot pointer.
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* Free slots are merged together by free().
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*/
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extern char *sbrk(), *brk();
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static char *bottom, *top;
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static char *_bottom, *_top, *_empty;
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static grow(len)
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unsigned len;
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{
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register char *p;
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register int click = CLICK_SIZE;
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p = sbrk(0);
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len += (char *) ALIGN((vir_bytes) p, sizeof(char *)) - p;
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while (click >= 4) {
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unsigned len1 = ALIGN((vir_bytes) p + len + sizeof(char *), click) - (vir_bytes) p;
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char *p1 = p;
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if (p + len1 + BUGFIX < p || (p1 = sbrk(len1)) == (char *) -1) {
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click >>= 1;
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continue;
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}
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p = p1;
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if (top + sizeof(char *) != p) {
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/* someone else has done an sbrk */
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NEXT(top) = (char *) ((vir_bytes) p | BUSY);
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} else {
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for (p = bottom; NEXT(p) != 0; p = (char *) (* (vir_bytes *) p & ~BUSY))
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;
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}
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top = p + len1 - sizeof(char *);
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NEXT(p) = top;
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NEXT(top) = 0;
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return 1;
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}
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return 0;
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ASSERT(NextSlot(_top) == 0);
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p = (char *) Align((ptrint)_top + len, BRKSIZE);
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if (p < _top || brk(p) != 0)
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return(0);
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NextSlot(_top) = p;
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NextSlot(p) = 0;
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free(_top);
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_top = p;
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return(1);
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}
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char *malloc(size)
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unsigned size;
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{
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register char *p, *next, *new;
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register unsigned len = ALIGN(size, sizeof(char *)) + sizeof(char *);
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register char *prev, *p, *next, *new;
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register unsigned len, ntries;
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if ((p = bottom) == 0) {
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p = sbrk(sizeof(char *));
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sbrk((char *) ALIGN((vir_bytes) p, sizeof(char *)) - p);
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p = (char *) ALIGN((vir_bytes) p, sizeof(char *));
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top = bottom = p;
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NEXT(p) = 0;
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}
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while ((next = NEXT(p)) != 0)
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if ((vir_bytes) next & BUSY) /* already in use */
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p = (char *) ((vir_bytes) next & ~BUSY);
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else {
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while ((new = NEXT(next)) != 0 && !((vir_bytes) new & BUSY))
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next = new;
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if (next - p >= len) { /* fits */
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if ((new = p + len) < next) /* too big */
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NEXT(new) = next;
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NEXT(p) = (char *) ((vir_bytes) new | BUSY);
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return(p + sizeof(char *));
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}
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p = next;
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if (size == 0)
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size = PTRSIZE; /* avoid slots less that 2*PTRSIZE */
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for (ntries = 0; ntries < 2; ntries++) {
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len = Align(size, PTRSIZE) + PTRSIZE;
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if (_bottom == 0) {
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p = sbrk(2 * PTRSIZE);
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p = (char *) Align((ptrint)p, PTRSIZE);
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p += PTRSIZE;
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_top = _bottom = p;
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NextSlot(p) = 0;
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}
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return grow(len) ? malloc(size) : 0;
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#ifdef SLOWDEBUG
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for (p = _bottom; (next = NextSlot(p)) != 0; p = next)
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ASSERT(next > p);
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ASSERT(p == _top);
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#endif
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for (prev = 0, p = _empty; p != 0; prev = p, p = NextFree(p)) {
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next = NextSlot(p);
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new = p + len;
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if (new > next)
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continue; /* too small */
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if (new + PTRSIZE < next) { /* too big, so split */
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/* + PTRSIZE avoids tiny slots on free list */
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NextSlot(new) = next;
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NextSlot(p) = new;
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NextFree(new) = NextFree(p);
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NextFree(p) = new;
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}
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if (prev)
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NextFree(prev) = NextFree(p);
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else
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_empty = NextFree(p);
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return(p);
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}
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if (grow(len) == 0)
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break;
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}
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ASSERT(ntries != 2);
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return(0);
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}
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char *realloc(old, size)
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char *old;
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unsigned size;
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{
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register char *p = old - sizeof(char *), *next, *new;
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register unsigned len = ALIGN(size, sizeof(char *)) + sizeof(char *), n;
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register char *prev, *p, *next, *new;
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register unsigned len, n;
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next = (char *) (* (vir_bytes *) p & ~BUSY);
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n = next - old; /* old size */
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while ((new = NEXT(next)) != 0 && !((vir_bytes) new & BUSY))
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next = new;
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if (next - p >= len) { /* does it still fit */
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if ((new = p + len) < next) { /* even too big */
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NEXT(new) = next;
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NEXT(p) = (char *) ((vir_bytes) new | BUSY);
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len = Align(size, PTRSIZE) + PTRSIZE;
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next = NextSlot(old);
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n = (int)(next - old); /* old length */
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/*
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* extend old if there is any free space just behind it
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*/
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for (prev = 0, p = _empty; p != 0; prev = p, p = NextFree(p)) {
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if (p > next)
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break;
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if (p == next) { /* 'next' is a free slot: merge */
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NextSlot(old) = NextSlot(p);
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if (prev)
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NextFree(prev) = NextFree(p);
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else
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_empty = NextFree(p);
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next = NextSlot(old);
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break;
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}
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}
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new = old + len;
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/*
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* Can we use the old, possibly extended slot?
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*/
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if (new <= next) { /* it does fit */
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if (new + PTRSIZE < next) { /* too big, so split */
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/* + PTRSIZE avoids tiny slots on free list */
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NextSlot(new) = next;
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NextSlot(old) = new;
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free(new);
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}
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else
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NEXT(p) = (char *) ((vir_bytes) next | BUSY);
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return(old);
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}
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if ((new = malloc(size)) == 0) /* it didn't fit */
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if ((new = malloc(size)) == 0) /* it didn't fit */
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return(0);
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bcopy(old, new, n); /* n < size */
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* (vir_bytes *) p &= ~BUSY;
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bcopy(old, new, n); /* n < size */
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free(old);
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return(new);
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}
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free(p)
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char *p;
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{
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* (vir_bytes *) (p - sizeof(char *)) &= ~BUSY;
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register char *prev, *next;
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ASSERT(NextSlot(p) > p);
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for (prev = 0, next = _empty; next != 0; prev = next, next = NextFree(next))
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if (p < next)
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break;
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NextFree(p) = next;
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if (prev)
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NextFree(prev) = p;
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else
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_empty = p;
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if (next) {
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ASSERT(NextSlot(p) <= next);
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if (NextSlot(p) == next) { /* merge p and next */
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NextSlot(p) = NextSlot(next);
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NextFree(p) = NextFree(next);
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}
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}
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if (prev) {
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ASSERT(NextSlot(prev) <= p);
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if (NextSlot(prev) == p) { /* merge prev and p */
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NextSlot(prev) = NextSlot(p);
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NextFree(prev) = NextFree(p);
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}
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}
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}
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#ifdef DEBUG
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static assert_failed()
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{
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write(2, "assert failed in lib/malloc.c\n", 30);
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abort();
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}
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#endif
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