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