154 lines
2.9 KiB
C
154 lines
2.9 KiB
C
#include <stdlib.h>
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#include <stdint.h>
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#include <unistd.h>
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#include "malloc.h"
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#if ACKCONF_WANT_MALLOC
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block_t __mem_root = { &__mem_root, 0 };
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block_t* __mem_freelist = &__mem_root;
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/* Pulls more memory from the system. */
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static block_t* brkmore(size_t nb)
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{
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uintptr_t bytes;
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block_t* p;
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if (nb < BRKSIZE)
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nb = BRKSIZE;
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bytes = nb * sizeof(block_t);
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/* Danger, will robinson! sbrk's parameter is *signed*... but malloc() takes a
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* size_t. */
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if (bytes > INTPTR_MAX)
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return NULL;
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p = sbrk(bytes);
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if (p == (block_t*)-1)
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return NULL;
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/* Add it to the free list by pretending it's a used block and freeing it. */
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p->size = nb;
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free(p + 1);
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return __mem_freelist;
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}
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void* malloc(size_t size)
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{
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block_t* p;
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block_t* prev;
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size_t nblocks;
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/* Add on space for the header; make sure we allocate a round number
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* of blocks; avoid overflow. */
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nblocks = BLOCKCOUNT(size);
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if (nblocks < size)
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return NULL;
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nblocks /= sizeof(block_t);
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prev = __mem_freelist;
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p = prev->next;
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for (;;)
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{
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if (p->size == nblocks)
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{
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/* We found a hole of exactly the right size. Unlink and return it.
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* The size field is already set. */
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prev->next = p->next;
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__mem_freelist = prev;
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return (void*)(p + 1);
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}
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else if (p->size > nblocks)
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{
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/* We found a hole bigger than we need. We shrink the hole and return
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* what's left. */
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p->size -= nblocks;
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p += p->size; /* p now points at our new block */
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p->size = nblocks;
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__mem_freelist = prev;
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return (void*)(p + 1);
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}
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if (p == __mem_freelist)
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{
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/* Uh-oh --- we've gone right round the ring and haven't found
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* anything. Get more memory from the system and keep going. */
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p = brkmore(nblocks);
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if (!p)
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return NULL;
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}
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prev = p;
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p = p->next;
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}
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}
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void free(void* ptr)
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{
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block_t* h = BLOCKOF(ptr);
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block_t* p;
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if (!ptr)
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return;
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/* __mem_freelist points into an ordered ring of free blocks. First,
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* we run around the ring until we find the last block before this one.
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*/
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p = __mem_freelist;
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for (;;)
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{
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/* Is h between p and the block after p? If so, h needs to be inserted
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* after p, so stop here. */
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if ((p < h) && (h < p->next))
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break;
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/* Is p the last block before the end of the address space? */
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if (p >= p->next)
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{
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/* Is h after p? (That is, will it become the new last block?) */
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if (p < h)
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break;
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/* Is h going to become the new *first* block? */
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if (h < p->next)
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break;
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}
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p = p->next;
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}
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/* If we can, merge the next block onto the end of h. */
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if ((h + h->size) == p->next)
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{
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h->size += p->next->size;
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h->next = p->next->next;
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}
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else
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{
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/* Otherwise, insert h before p->next. */
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h->next = p->next;
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}
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/* Now try to merge h onto the end of p. */
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if ((p + p->size) == h)
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{
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p->size += h->size;
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p->next = h->next;
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}
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else
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{
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/* Okay, we couldn't do the merge. Fix up the linked list. */
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p->next = h;
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}
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/* ...and update the ring pointer. */
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__mem_freelist = p;
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}
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#endif
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