is this code bugfree?
if yes, I'll commit this to the library.
Please consider including BSD license and send the complete coe as
attachement.
cheers,
~d
On Wednesday 21 January 2004 22:11, soltras wrote:
> Lately I found the bug in my mymalloc function.
> Change really is in below lines:
> if (xsize == 0x7FFF) f = 1; //was (xsize<<1)+2 == 0) // 0x7FFF
> means
> empty else{
> heap_next = &heap_top[xsize + 1];
> 1: if(heap_next >= heap_bottom ) f = 1;//f=1 mean do loop once and
> end if
> you reach over stack
> }
>
> The basic disadvantage of below code is the way of description bit
> allocation. When You overrun buffer you almost loose all data ie:
> char * buffer = "abcd";
> char* ptr = mymalloc(4); //you overrun buffer because '\0' deletes next and
> all above allocations. Moreover this improvement prevents deleting stack.
> however I have no idea where to put malloc information data. All ideas have
> pros and cons.
>
>
>
> all code is below:
> //released under GNU PUBLIC LICENCE
> #include <stdlib.h>
>
> #define XSIZE(x) ((*x)>>1)
> #define FREE_P(x) (!((*x)&1))
> #define MARK_BUSY(x) ((*x)|=1)
> #define MARK_FREE(x) ((*x)&=0xfffe)
>
> //extern size_t __bss_end;
> extern size_t __noinit_end;
> #define GET_HEAP_BOTTOM(__x) __asm__ __volatile__("mov r1, %0": "=r"
> ((uint16_t)__x) :)
>
> void myfree (void *p);
> void *mymalloc (size_t size);
>
> void *mymalloc (size_t size)
> {
> static char once;
> size_t * heap_bottom;
> size_t * heap_top = &__noinit_end;
> size_t * heap_next;
> size_t xsize;
> char f = 0;
>
> if (!once)
> {
> once = 1;
> *heap_top = 0xFFFE;
> }
> GET_HEAP_BOTTOM (heap_bottom);
> heap_bottom -= 20;
>
> size = (size+1)>>1; /* round to 2 */
> do
> {
> xsize = XSIZE (heap_top);
> if (xsize == 0x7FFF) f = 1; //(xsize<<1)+2 == 0)
> else{
> heap_next = &heap_top[xsize + 1];
> if(heap_next >= heap_bottom ) f = 1;
> }
>
> if (FREE_P (heap_top))
> {
> if (f>0)
> {
> xsize = heap_bottom - heap_top - 1;//(heap_b - heap_t)/2 in
> fact
> }
> else if (FREE_P(heap_next))
> {
> *heap_top = ( (XSIZE(heap_next)== 0x7FFF)/*<<1) + 2 == 0*/
> ? 0xFFFE
>
> : (xsize + XSIZE(heap_next) + 1)<<1);
>
> continue;
> }
>
>
> if (xsize >= size)
> {
>
> if (f>0)
> heap_top[size + 1] = 0xFFFE;
> else if (xsize != size)
> heap_top[size + 1] = (xsize - size - 1) << 1;
> *heap_top = size << 1;
> MARK_BUSY (heap_top);
> return heap_top+1;
> }
> }
> heap_top += xsize + 1;
> }
> while (!f);
> return NULL;
> }
>
> void myfree (void *p)
> {
> size_t *t = (size_t*)p - 1;
> MARK_FREE (t);
> }
>
>
>
>
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