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118 lines
3.5 KiB
118 lines
3.5 KiB
/*
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* Yet Another Malloc
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* ya_block.h
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*/
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/* Block layout:
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*
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* -2 -1 0 size-4 size-3
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* +------+------+-------- - - - - - - - --------+------+------+
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* | prev | size | data... | size | next |
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* +------+------+-------- - - - - - - - --------+------+------+
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*
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*/
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#ifndef YA_BLOCK_H
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#define YA_BLOCK_H
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/*----------*/
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/* Includes */
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/*----------*/
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#include <stddef.h> // for size_t
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#include <stdint.h> // for intptr_t
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#include <stdbool.h>
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/*---------*/
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/* Externs */
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/*---------*/
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extern intptr_t *heap_start; // with space for 2 words before
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extern intptr_t *heap_end ; // first block outside heap
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/*---------*/
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/* Inlines */
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/*---------*/
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/* Returns true iff the boundary tag has the allocated bit set. */
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static inline bool tag_is_alloc(intptr_t tag) {
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return tag & 1;
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}
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/* Returns true iff the block's boundary tag has the allocated bit set. */
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static inline bool block_is_alloc(intptr_t *block) {
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return tag_is_alloc(block[-1]);
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}
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/* Returns the size stored in the boundary tag. */
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static inline intptr_t tag_size(intptr_t tag) {
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return tag & -2;
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}
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/* Returns the size stored in the block's boundary tag. */
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static inline intptr_t block_size(intptr_t *block) {
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return tag_size(block[-1]);
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}
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/*--------------*/
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/* Declarations */
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/*--------------*/
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/* Initializes the heap by calling sbrk to allocate some starter memory.
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* Sets heap_start and heap_end to their appropriate values.
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* Returns the pointer to the start of the heap or NULL in case of failure. */
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intptr_t *heap_init();
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/* Extends the heap enough for the last block to be at least n_bytes bytes
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* large by calling sbrk.
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* Returns a pointer to the last (free) block or NULL in case of failure. */
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intptr_t *heap_extend(size_t n_bytes);
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#ifdef YA_DEBUG
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/* Prints each block in the range from the block at start to the one at end */
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void block_print_range(intptr_t *start, intptr_t *end);
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/* Checks the heap and each block for consistency.
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* Does not check the free list.
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* Returns -1 on error, the total number of free blocks otherwise. */
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int heap_check();
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#endif
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/* Initializes the block's boundary tags. */
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void block_init(intptr_t *block, intptr_t size);
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/* Sets the allocated bit in the block's boundary tags. */
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void block_alloc(intptr_t *block);
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/* Erases the allocated bit in the block's boundary tags. */
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void block_free(intptr_t *block);
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/* Fills block with zeros. */
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void block_clear(intptr_t *block);
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/* Returns the size in words of the smallest block that can
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* store n_bytes bytes. Takes alignment and boundary tags into account */
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intptr_t block_fit(size_t n_bytes);
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/* Tries to coalesce a block with its previous neighbor.
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* Returns a pointer to the coalesced block. */
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intptr_t *block_join_prev(intptr_t *block);
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/* Tries to colesce a block with its next neighbor.
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* Returns the unchanged pointer to the block. */
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intptr_t *block_join_next(intptr_t *block);
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/* Tries to coalesce a block with its previous and next neighbors.
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* Returns a pointer to the coalesced block. */
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intptr_t *block_join(intptr_t *block);
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/* Split the block [block_size] into [size, block_size - size] if possible
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* Returns a pointer to the second block or NULL if no split occurred. */
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intptr_t *block_split(intptr_t *block, intptr_t size);
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/* Try to find a free block at least min_size words large by walking the
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* boundary tags. Does not grow the heap.
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* Returns a pointer to the block or NULL in case of failure. */
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intptr_t *block_find(intptr_t min_size);
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#endif
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