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#include <stddef.h>
#include <stdint.h>
#include "string.h"
#include "malloc.h"
void * sbrk(ptrdiff_t incr);
typedef struct _heap_t {
void * ptr;
size_t size;
struct _heap_t * prev, * next;
} heap_t;
static void * heap_base = NULL;
static heap_t * head = NULL, * tail = NULL;
static heap_t * find_fit(heap_t * head, size_t size) {
heap_t * prev = head;
uintptr_t prev_top, next_bot;
while (prev) {
if (prev->next) {
prev_top = (uintptr_t) prev->ptr + prev->size;
next_bot = (uintptr_t) prev->next - prev_top;
if (next_bot >= size)
return prev;
}
prev = prev->next;
}
return prev;
}
void * base_malloc(size_t size) {
void * ptr = NULL, * heap_ptr;
heap_t * new, * prev;
size = (size + sizeof(heap_t) + 7) & ~7;
// Nothing's initialized yet ? Let's just initialize the bottom of our heap,
// flag it as allocated.
if (!head) {
if (!heap_base)
heap_base = sbrk(0);
heap_ptr = sbrk(size);
if (!heap_ptr)
return NULL;
ptr = (void *) ((uintptr_t) heap_ptr + sizeof(heap_t));
head = (heap_t *) heap_ptr;
head->ptr = ptr;
head->size = size - sizeof(heap_t);
head->prev = NULL;
head->next = NULL;
tail = head;
return ptr;
}
// We *may* have the bottom of our heap that has shifted, because of a free.
// So let's check first if we have free space there, because I'm nervous
// about having an incomplete data structure.
if (((uintptr_t) heap_base + size) < (uintptr_t) head) {
new = (heap_t *) heap_base;
ptr = (void *) ((uintptr_t) new + sizeof(heap_t));
new->ptr = ptr;
new->size = size - sizeof(heap_t);
new->prev = NULL;
new->next = head;
head->prev = new;
head = new;
return ptr;
}
// No luck at the beginning of the heap, let's walk the heap to find a fit.
prev = find_fit(head, size);
if (prev) {
new = (heap_t *) ((uintptr_t) prev->ptr + prev->size);
ptr = (void *) ((uintptr_t) new + sizeof(heap_t));
new->ptr = ptr;
new->size = size - sizeof(heap_t);
new->prev = prev;
new->next = prev->next;
new->next->prev = new;
prev->next = new;
return ptr;
}
// Time to extend the size of the heap.
heap_ptr = sbrk(size);
if (!heap_ptr)
return NULL;
ptr = (void *) ((uintptr_t) heap_ptr + sizeof(heap_t));
new = (heap_t *) heap_ptr;
new->ptr = ptr;
new->size = size - sizeof(heap_t);
new->prev = tail;
new->next = NULL;
tail->next = new;
tail = new;
return ptr;
}
void * base_realloc(void * ptr, size_t size) {
heap_t * prev;
void * new = NULL;
if (!size && ptr) {
free(ptr);
return NULL;
}
if (!ptr)
return malloc(size);
size = (size + sizeof(heap_t) + 7) & ~7;
prev = (heap_t *) ((uintptr_t) ptr - sizeof(heap_t));
// New memory block shorter ?
if (prev->size >= size) {
prev->size = size;
if (!prev->next)
sbrk(ptr + size - sbrk(0));
return ptr;
}
// New memory block larger
// Is it the last one ?
if (!prev->next) {
new = sbrk(size - prev->size);
if (!new)
return NULL;
prev->size = size;
return ptr;
}
// Do we have free memory after it ?
if ((prev->next->ptr - ptr) > size) {
prev->size = size;
return ptr;
}
// No luck.
new = malloc(size);
if (!new)
return NULL;
memcpy(new, ptr, prev->size);
free(ptr);
return new;
}
void base_free(void * ptr) {
heap_t * cur;
void * top;
size_t size;
if (!ptr || !head)
return;
// First block; bumping head ahead.
if (ptr == head->ptr) {
size = head->size + (size_t) (head->ptr - (void *) head);
head = head->next;
if (head) {
head->prev = NULL;
} else {
tail = NULL;
sbrk(-size);
}
return;
}
// Finding the proper block
cur = head;
for (cur = head; ptr != cur->ptr; cur = cur->next)
if (!cur->next)
return;
if (cur->next) {
// In the middle, just unlink it
cur->next->prev = cur->prev;
} else {
// At the end, shrink heap
tail = cur->prev;
top = sbrk(0);
size = (top - cur->prev->ptr) - cur->prev->size;
sbrk(-size);
}
cur->prev->next = cur->next;
}
__attribute__((weak)) void * __builtin_new(size_t size) { return malloc(size); }
__attribute__((weak)) void __builtin_delete(void * ptr) { free(ptr); }
malloc_t malloc = base_malloc;
free_t free = base_free;
realloc_t realloc = base_realloc;
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