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#include <stdlib.h>
#include <string.h>
typedef unsigned int uint;
enum
{
MAGIC = 0xbada110c,
MAX2SIZE = 32,
CUTOFF = 12,
};
typedef struct Bucket Bucket;
struct Bucket
{
int size;
int magic;
Bucket *next;
int pad;
char data[1];
};
typedef struct Arena Arena;
struct Arena
{
Bucket *btab[MAX2SIZE];
};
static Arena arena;
#define datoff ((int)((Bucket*)0)->data)
#define nil ((void*)0)
extern void *sbrk(unsigned long);
void*
malloc(size_t size)
{
uint next;
int pow, n;
Bucket *bp, *nbp;
for(pow = 1; pow < MAX2SIZE; pow++) {
if(size <= (1<<pow))
goto good;
}
return nil;
good:
/* Allocate off this list */
bp = arena.btab[pow];
if(bp) {
arena.btab[pow] = bp->next;
if(bp->magic != 0)
abort();
bp->magic = MAGIC;
return bp->data;
}
size = sizeof(Bucket)+(1<<pow);
size += 7;
size &= ~7;
if(pow < CUTOFF) {
n = (CUTOFF-pow)+2;
bp = sbrk(size*n);
if((int)bp < 0)
return nil;
next = (uint)bp+size;
nbp = (Bucket*)next;
arena.btab[pow] = nbp;
for(n -= 2; n; n--) {
next = (uint)nbp+size;
nbp->next = (Bucket*)next;
nbp->size = pow;
nbp = nbp->next;
}
nbp->size = pow;
}
else {
bp = sbrk(size);
if((int)bp < 0)
return nil;
}
bp->size = pow;
bp->magic = MAGIC;
return bp->data;
}
void
free(void *ptr)
{
Bucket *bp, **l;
if(ptr == nil)
return;
/* Find the start of the structure */
bp = (Bucket*)((uint)ptr - datoff);
if(bp->magic != MAGIC)
abort();
bp->magic = 0;
l = &arena.btab[bp->size];
bp->next = *l;
*l = bp;
}
void*
realloc(void *ptr, size_t n)
{
void *new;
uint osize;
Bucket *bp;
if(ptr == nil)
return malloc(n);
/* Find the start of the structure */
bp = (Bucket*)((uint)ptr - datoff);
if(bp->magic != MAGIC)
abort();
/* enough space in this bucket */
osize = 1<<bp->size;
if(osize >= n)
return ptr;
new = malloc(n);
if(new == nil)
return nil;
memmove(new, ptr, osize);
free(ptr);
return new;
}
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