134 lines
2.6 KiB
C
134 lines
2.6 KiB
C
#include <stddef.h>
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#include <stdio.h>
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#include <unistd.h>
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#define ALIGN4(s) (((((s)-1)>>2)<<2)+4)
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#define BLOCK_SIZE sizeof(struct block)
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/// The memory block's header.
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struct block
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{
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size_t size;
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struct block* next;
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int free;
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};
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struct block* freeList = NULL;
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/// Extends heap memory upwards, towards zero.
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/// @param [in] last The last block that the newly created block will link to.
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/// @param [in] s The size of the memory needed aligned by 4 bytes.
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/// @returns The new memory block.
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struct block* extend_heap(struct block* last, size_t s)
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{
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struct block* b = sbrk(0);
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if (sbrk(BLOCK_SIZE + s) == (void*)-1)
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return NULL;
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b->size = s;
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b->next = NULL;
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b->free = 0;
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if (last)
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last->next = b;
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return b;
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}
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/// Finds the first block that will fit the given size.
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/// @param [in] s The 4 byte aligned size to look for.
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/// @returns The matching available memory block.
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struct block* find_first(size_t s)
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{
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struct block* current = freeList;
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while (current && (!current->free || current->size < s))
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current = current->next;
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return current;
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}
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/// Finds the last memory block in the linked list to attach a new block to.
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/// @returns The last memory block.
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struct block* find_last()
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{
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struct block* current = freeList;
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while (current && current->next)
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current = freeList->next;
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return current;
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}
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/// Will find or allocate a memory block.
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/// @param [in] size The size of the memory block to request.
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/// @returns The requested memory on the heap.
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/// @todo Fragmenting functionality.
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void* malloc(size_t size)
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{
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struct block* b;
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size_t alignedSize = ALIGN4(size);
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if (freeList)
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{
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b = find_first(alignedSize);
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if (!b)
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b = extend_heap(find_last(), alignedSize);
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/*
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else
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Fragment here if possible.
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*/
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}
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else
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{
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b = extend_heap(NULL, alignedSize);
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if (!b)
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return NULL;
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freeList = b;
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}
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return b + 1;
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}
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/// Will flag the provided memory as free and will defragment other blocks adjacent to it.
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/// @param [in] ptr The memory to flag as free.
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/// @note If all data after the provided memory is free, it will reduce the heap size.
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/// @todo Reverse defragmenting.
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void free(void* ptr)
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{
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if (!ptr)
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return;
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struct block* b = (struct block*)ptr - 1;
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b->free = 1;
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struct block* link = b->next;
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while (b->next && b->next->free)
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{
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b->size += BLOCK_SIZE + b->next->size;
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b->next = link->next;
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}
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// Reverse defragment here.
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if (!b->next)
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brk(b);
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}
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int main()
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{
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int* a = (int*)malloc(sizeof(int));
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int* b = (int*)malloc(sizeof(int));
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*a = 5;
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*b = 12;
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printf("Test 1: %i\n", *a);
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printf("Test 2: %i", *b);
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free(b);
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free(a);
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return 0;
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} |