minix/lib/syslib/kmalloc.c
2005-04-21 14:53:53 +00:00

177 lines
4 KiB
C
Executable file

/* malloc(), realloc(), free() - simple memory allocation routines
*
* This is a very small and simple minded malloc Author: Kees J. Bot
* implementation. Ideal for things like a 29 Jan 1994
* bootstrap program, or for debugging. Six times
* slower than any good malloc.
*/
#define nil 0
#define sbrk _sbrk
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <limits.h>
#if !DEBUG
#define NDEBUG 1
#define debug(expr) ((void) 0)
#else
#define debug(expr) expr
#endif
#include <assert.h>
typedef struct cell {
size_t size; /* Size of a malloc()'ed object. */
#if DEBUG
unsigned magic; /* To recognize a cell. */
#endif
struct cell *next; /* Next cell on the free list. */
#if DEBUG
unsigned sacred; /* Don't touch while unallocated. */
#endif
} cell_t;
#if UINT_MAX <= 0xFFFF
#define MAGIC 0x537B
#else
#define MAGIC 0x537BC0D8
#endif
/* Size of the header of an object. */
#define HDR_SIZE offsetof(cell_t, next)
/* An offset from a cell pointer to a next cell. */
#define offset(cp, size) ((cell_t *) ((char *) (cp) + (size)))
/* Address of the object in a cell and back. */
#define cell2obj(cp) ((void *) ((char *) (cp) + HDR_SIZE))
#define obj2cell(op) ((cell_t *) ((char *) (op) - HDR_SIZE))
/* The free list. */
static cell_t *freelist;
void *malloc(size_t size)
/* Allocate an object of at least the given size. */
{
cell_t **pcp, *cp;
size += HDR_SIZE;
if (size < sizeof(cell_t)) size= sizeof(cell_t);
/* Align to a word. Use a real malloc if you need better alignment. */
size= (size + sizeof(int) - 1) & ~(sizeof(int) - 1);
/* Space for a magic number at the end of the chunk. */
debug(size += sizeof(unsigned));
for (;;) {
/* Do a first fit search. */
pcp= &freelist;
while ((cp= *pcp) != nil) {
cell_t *next= cp->next;
assert(cp->magic == MAGIC);
assert(cp->sacred == MAGIC);
if (offset(cp, cp->size) == next) {
/* Join adjacent free cells. */
assert(next->magic == MAGIC);
assert(next->sacred == MAGIC);
cp->size+= next->size;
cp->next= next->next;
continue; /* Try again. */
}
if (size <= cp->size) break; /* Big enough. */
/* Next cell. */
pcp= &cp->next;
}
if (cp != nil) break; /* Found a big enough chunk. */
/* Allocate a new chunk at the break. */
if ((cp= (cell_t *) sbrk(size)) == (cell_t *) -1) {
return nil;
}
cp->size= size;
cp->next= nil;
debug(cp->magic= MAGIC);
debug(cp->sacred= MAGIC);
*pcp= cp;
}
/* We've got a cell that is big enough. Can we break it up? */
if (cp->size >= size + sizeof(cell_t)) {
cell_t *next= offset(cp, size);
next->size= cp->size - size;
next->next= cp->next;
debug(next->magic= MAGIC);
debug(next->sacred= MAGIC);
cp->size= size;
cp->next= next;
}
/* Unchain the cell we've found and return an address in it. */
*pcp= cp->next;
debug(memset(cell2obj(cp), 0xAA, cp->size - HDR_SIZE));
debug(((unsigned *) offset(cp, cp->size))[-1]= MAGIC);
return cell2obj(cp);
}
void free(void *op)
/* Deallocate an object. */
{
cell_t **prev, *next, *cp;
if (op == nil) return; /* Aaargh. */
cp= obj2cell(op);
assert(cp->magic == MAGIC);
assert(((unsigned *) offset(cp, cp->size))[-1] == MAGIC);
debug(cp->sacred= MAGIC);
/* Find the spot where the object belongs. */
prev= &freelist;
while ((next= *prev) != nil && next < cp) {
assert(next->magic == MAGIC);
assert(next->sacred == MAGIC);
prev= &next->next;
}
/* Put the new free cell in the list. */
*prev= cp;
cp->next= next;
#if DEBUG
/* Check the rest of the list. */
while (next != nil) {
assert(next->magic == MAGIC);
assert(next->sacred == MAGIC);
next= next->next;
}
#endif
}
void *realloc(void *op, size_t size)
/* Change the size of an object. Don't bother being smart, just copy it. */
{
size_t oldsize;
void *new;
oldsize= op == nil ? 0 : obj2cell(op)->size - HDR_SIZE;
new= malloc(size);
memcpy(new, op, oldsize > size ? size : oldsize);
free(op);
return new;
}
/*
* $PchId: malloc.c,v 1.4 1996/02/22 09:15:56 philip Exp $
*/