mymalloc.c
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#include "mymalloc.h"
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
typedef struct _blkdata {
unsigned long size; /* rozmiar bloku wlaczajac naglowek */
unsigned int flags;
} blkdata;
#define MM_OCCUPIED 1
#define MM_LAST 2
static void* begin;
int mymalloc_init(unsigned long size)
{
blkdata* b;
assert(size > 0);
begin = sbrk(size);
if (!begin)
return 0;
b = (blkdata*)begin;
b->size = size;
b->flags = MM_LAST;
return 1;
};
void* mymalloc(unsigned long size)
{
blkdata* b = (blkdata*)begin;
printf("Request to allocate %lu bytes\n", size);
while (1) {
if ((b->size > size + sizeof(blkdata)) && !(b->flags & MM_OCCUPIED)) {
unsigned long after = b->size - size - sizeof(blkdata);
if (after > sizeof(blkdata)) {
blkdata* na = (blkdata*)((void*)b + size + sizeof(blkdata));
na->flags = 0;
if (b->flags & MM_LAST)
na->flags |= MM_LAST;
na->size = after;
b->size = size + sizeof(blkdata);
b->flags = MM_OCCUPIED;
return ((void*)b) + sizeof(blkdata);
}
else /* wez caly blok */
{
b->flags |= MM_OCCUPIED;
return ((void*)b) + sizeof(blkdata);
}
};
if (b->flags & MM_LAST)
break;
b = (blkdata*)((void*)b + b->size);
};
return NULL;
}
void myfree(void* ptr)
{
blkdata* b;
blkdata* nextb = NULL;
blkdata* prevb = NULL;
if (ptr == NULL)
return;
b = (blkdata*)(ptr - sizeof(blkdata));
printf("Request to free %lu bytes at the address %p\n",
b->size - sizeof(blkdata), b);
if ((void*)b != begin) {
/* znajdz poprzedni blok */
prevb = (blkdata*)begin;
while (1) {
blkdata* next;
assert(!(prevb->flags & MM_LAST));
next = (blkdata*)((void*)prevb + prevb->size);
if (next == b)
break;
prevb = next;
};
};
/* znajdz nastepny blok */
if (!(b->flags & MM_LAST))
nextb = (blkdata*)((void*)b + b->size);
/* zaznacz blok jako wolny */
b->flags &= ~MM_OCCUPIED;
/* skonsoliduj z nastepnym */
if (nextb && !(nextb->flags & MM_OCCUPIED)) {
if (nextb->flags & MM_LAST)
b->flags = MM_LAST;
b->size += nextb->size;
}
/* skonsoliduj z poprzednim */
if (prevb && !(prevb->flags & MM_OCCUPIED)) {
if (b->flags & MM_LAST)
prevb->flags |= MM_LAST;
prevb->size += b->size;
};
}
static void* copyrealloc(void* ptr, unsigned long size, unsigned long oldsize)
{
void* blk = mymalloc(size);
if (blk == NULL)
return NULL;
memcpy(blk, ptr, oldsize);
myfree(ptr);
return blk;
}
void* myrealloc(void* ptr, unsigned long size)
{
blkdata* b;
if (ptr == NULL)
return mymalloc(size);
b = (blkdata*)(ptr - sizeof(blkdata));
printf("Request to reallocate %lu bytes to %lu bytes, old address=%p\n",
b->size - sizeof(blkdata), size, b);
if (size == 0) {
myfree(ptr);
return NULL;
};
if (size <= b->size - sizeof(blkdata)) /* zmniejszenie bloku */
{
unsigned long after = b->size - size - sizeof(blkdata);
blkdata* nextb = NULL;
if (!(b->flags & MM_LAST))
nextb = (blkdata*)((void*)b + b->size);
blkdata* na = ((void*)b) + size + sizeof(blkdata);
if (nextb && !(nextb->flags & MM_OCCUPIED))
/* skonsoliduj z nastepnym */
{
unsigned int flags = nextb->flags;
unsigned long size = after + nextb->size;
na->flags = flags;
na->size = size;
b->size = size + sizeof(blkdata);
}
else if (after > sizeof(blkdata)) {
na->flags = 0;
if (b->flags & MM_LAST)
na->flags |= MM_LAST;
na->size = after;
b->size = size + sizeof(blkdata);
b->flags = MM_OCCUPIED;
}
return ptr;
}
else /* zwiekszenie bloku */
{
blkdata* next = (blkdata*)((void*)b + b->size);
if (!(b->flags & MM_LAST) && !(next->flags & MM_OCCUPIED)) {
unsigned long totalsize = b->size + next->size;
unsigned long after = totalsize - size - sizeof(blkdata);
if (size + sizeof(blkdata) >
totalsize) /* brak miejsca w nastepnym bloku */
return copyrealloc(ptr, size, b->size - sizeof(blkdata));
if (next->flags & MM_LAST)
b->flags |= MM_LAST;
if (after > sizeof(blkdata)) {
blkdata* na = (blkdata*)((void*)b + size + sizeof(blkdata));
na->flags = 0;
if (b->flags & MM_LAST)
na->flags |= MM_LAST;
na->size = after;
b->size = size + sizeof(blkdata);
b->flags = MM_OCCUPIED;
}
else
b->size += next->size;
return ptr;
}
else /* nastepny zajety albo biezacy ostatni */
return copyrealloc(ptr, size, b->size - sizeof(blkdata));
}
}
void mymalloc_dump()
{
blkdata* b = (blkdata*)begin;
unsigned long totalsize = 0;
printf("Mymalloc block list dump\n");
while (1) {
printf("Block at the address %p flags %c%c size %lu\n", b,
(b->flags & MM_OCCUPIED) ? 'O' : 'F',
(b->flags & MM_LAST) ? 'L' : ' ', b->size);
totalsize += b->size;
if (b->flags & MM_LAST)
break;
b = (blkdata*)((void*)b + b->size);
};
printf("Total size:%lu\n", totalsize);
}