Merge pull request 'gbowne1 version of implementation with more implementations done' (#4) from gbowne1_impl into main
Reviewed-on: #4
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commit
f341253aa8
233
main.c
233
main.c
@ -1,36 +1,39 @@
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#include <stddef.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <sys/syscall.h>
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#include <stdlib.h>
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#define ALIGN4(s) (((((s)-1)>>2)<<2)+4)
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#define ALIGN16(s) (((s) + 15) & ~0x0F)
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#define BLOCK_SIZE sizeof(struct block)
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#define MINIMUM_BLOCK_SIZE 4
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#define MINIMUM_BLOCK_SIZE (sizeof(struct block) + 16)
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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* prev;
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struct block* next;
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struct block *prev;
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struct block *next;
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int free;
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};
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struct block* first = NULL;
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struct block* last = NULL;
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struct block *first = NULL;
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struct block *last = NULL;
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/// Extends heap memory upwards, towards zero.
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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(size_t s)
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struct block *extend_heap(size_t s)
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{
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// Ensure the allocated size is at least the minimum block size
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if (s < MINIMUM_BLOCK_SIZE)
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s = MINIMUM_BLOCK_SIZE;
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struct block* b = (struct block*)syscall(SYS_brk, NULL);
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struct block *b = (struct block *)sbrk(0); // Get the current break
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if ((void*)syscall(SYS_brk, (char*)(b + 1) + s) == (void*)-1)
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// Add the size of the block header to the requested size
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s += BLOCK_SIZE;
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if (sbrk(s) == (void *)-1) // Extend the break by s bytes
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return NULL;
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b->size = s;
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@ -49,9 +52,9 @@ struct block* extend_heap(size_t s)
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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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struct block *find_first(size_t s)
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{
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struct block* current = first;
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struct block *current = first;
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while (current && (!current->free || current->size < s))
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current = current->next;
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@ -62,112 +65,204 @@ struct block* find_first(size_t s)
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/// @param [in] in The memory block to fragment.
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/// @param [in] s The size of the new memory block.
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/// @returns The new memory block.
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struct block* fragment_block(struct block* in, size_t s)
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struct block *fragment_block(struct block *in, size_t s)
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{
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size_t totalSize = BLOCK_SIZE + s;
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struct block* b = (struct block*)((char*)(in + 1) + (in->size - totalSize));
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b->size = s;
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b->prev = in;
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b->next = in->next;
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b->free = 0;
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// Calculate the size of the new block, including the block header
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size_t newBlockSize = s + BLOCK_SIZE;
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in->size -= totalSize;
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in->next = b;
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// Check if the current block can be split
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if (in->size <= newBlockSize)
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{
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// Cannot split, return the original block
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return in;
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}
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return b;
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// Calculate the size of the remainder block
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size_t remainderSize = in->size - newBlockSize;
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// Create the new block in the remainder space
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struct block *newBlock = (struct block *)((char *)(in + 1) + s);
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newBlock->size = remainderSize;
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newBlock->prev = in;
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newBlock->next = in->next;
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newBlock->free = 1; // Set the new block as free
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// Update the current block to reflect the reduced size
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in->size = newBlockSize;
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in->next = newBlock;
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// Insert the new block into the linked list of blocks
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if (newBlock->next)
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{
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newBlock->next->prev = newBlock;
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}
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return newBlock;
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}
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struct block *find_best_fit(size_t s)
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{
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struct block *current = first;
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struct block *best_fit = NULL;
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while (current)
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{
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if (current->free && current->size >= s)
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{
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if (best_fit && current->size < best_fit->size) // Check for NULL before comparison
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{
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{
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best_fit = current;
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}
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}
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current = current->next;
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}
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return best_fit;
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}
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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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void *malloc(size_t size)
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{
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struct block* b;
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if (size == 0)
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{
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return NULL;
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}
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size = ALIGN4(size);
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size = ALIGN16(size); // First align the requested size
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size_t total_size = size + BLOCK_SIZE; // Then add the size of the block header
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struct block *b;
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if (first)
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{
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b = find_first(size);
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b = find_best_fit(size);
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if (!b)
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b = extend_heap(size);
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else if (b->size > BLOCK_SIZE + size)
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{
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b = extend_heap(total_size);
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if (!b)
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{
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return NULL; // Check if heap extension failed
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}
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}
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else if (b->size > total_size + MINIMUM_BLOCK_SIZE)
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{
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b = fragment_block(b, size);
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}
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}
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else
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{
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b = extend_heap(size);
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b = extend_heap(total_size);
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if (!b)
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{
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return NULL;
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}
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first = b;
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}
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return b + 1;
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b->free = 0; // Mark the block as used
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return (char *)b + BLOCK_SIZE; // Return a pointer to the usable memory
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}
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void* realloc(void* ptr, size_t new_size)
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void *realloc(void *ptr, size_t new_size)
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{
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if (!ptr)
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{
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return malloc(new_size);
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}
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if (!new_size)
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if (new_size == 0)
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{
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free(ptr);
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return NULL;
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}
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struct block* b = (struct block*)ptr - 1;
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if (b->free)
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return NULL;
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struct block *b = (struct block *)((char *)ptr - BLOCK_SIZE);
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if (b->size >= new_size + BLOCK_SIZE)
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{
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return ptr; // The block is already big enough
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}
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if (b->size == new_size)
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return ptr;
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else if (b->size > BLOCK_SIZE + new_size)
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return fragment_block(b, new_size) + 1;
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void *new_ptr = malloc(new_size);
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if (!new_ptr)
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{
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return NULL; // Allocation failed
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}
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memcpy(new_ptr, ptr, b->size - BLOCK_SIZE); // Copy old data to new block, excluding the header size
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free(ptr); // Free the old block
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return NULL;
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return new_ptr;
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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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void free(void* ptr)
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void my_custom_free(void *ptr)
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{
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if (!ptr)
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return;
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if (!ptr)
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{
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return;
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}
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struct block* b = (struct block*)ptr - 1;
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if (b->free)
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return;
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struct block *b = (struct block *)((char *)ptr - BLOCK_SIZE);
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if (b->free)
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{
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fprintf(stderr, "Double free detected at block %p.\n", ptr);
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abort(); // Terminate the program immediately due to serious error
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}
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b->free = 1;
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b->free = 1;
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while (b->prev && b->prev->free)
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b = b->prev;
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// Coalesce free blocks
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while (b->prev && b->prev->free)
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{
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// Merge with previous block
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b->prev->size += BLOCK_SIZE + b->size;
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b->prev->next = b->next;
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b = b->prev;
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}
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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 = b->next->next;
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}
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// If there is a next block and it's free, merge with it
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if (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 = b->next->next;
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if (b->next)
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{
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b->next->prev = b;
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}
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}
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if (!b->next)
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syscall(SYS_brk, b);
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}
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// After merging, update the 'last' pointer if necessary
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if (!b->next)
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{
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last = b;
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}
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/// Retrieves the total heap usage in bytes.
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/// @returns Usage in bytes.
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size_t get_heap_size()
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{
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if (!first || !last)
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return 0;
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return ((char*)last + last->size) - (char*)first;
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// Check if we can shrink the heap
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if (b == last)
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{
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// Update 'last' to the previous block or NULL if there's no previous block
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last = b->prev;
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if (last)
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{
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last->next = NULL;
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}
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else
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{
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first = NULL;
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}
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// Reduce the program break to release the memory
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sbrk(0 - (b->size + BLOCK_SIZE));
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}
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}
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int main()
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{
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int* a = (int*)malloc(1);
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int* b = (int*)malloc(1);
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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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@ -179,7 +274,7 @@ int main()
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free(a);
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free(b);
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int* c = (int*)malloc(sizeof(int));
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int *c = (int *)malloc(sizeof(int));
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return 0;
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}
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