marCsweep/include/gc_malloc.h

#ifndef GC_MALLOC_H
#define GC_MALLOC_H

#include <stdint.h>
#include <unistd.h>

// Generally, inline functions are preferable to macros resembling functions.
// https://www.kernel.org/doc/html/v4.10/process/coding-style.html#data-structures

#define OVERHEAD 1 /* Number of 8-byte segments for chunk size & flags */
#define MAGIC 2 /* Number of 8-byte segments from top of chunk to fields */
#define MIN 3 /* Minimum number of 8-byte segments for data in a chunk */

/*
 * Metadata and user data for allocated memory
 *
 * footer: user data for previous chunk
 * size: size of chunk in bytes
 * merge: flag to identify when the chunk can be coalesced
 * free: flag to identify when the chunk is free
 * next: pointer to next chunk in the free list
 * prev: pointer to previous chunk in the free list
 */
struct gc_chunk {
	uint64_t footer;
	uint32_t size;
	uint16_t merge;
	uint16_t free;
	struct gc_chunk *next;
	struct gc_chunk *prev;
};

// Gets a pointer to the next chunk
struct gc_chunk *get_next_chunk(struct gc_chunk *curr);

// Gets a pointer to the previous chunk, ensuring that current can be coalesced
struct gc_chunk *get_prev_chunk(struct gc_chunk *curr);

// Updates chunk footer information
void set_footer(struct gc_chunk *curr);

// Gets footer information for the current chunk
int get_footer(struct gc_chunk *curr);

// Performs allocations of SIZE bytes
void *gc_malloc(size_t size);

// Frees blocks of memory allocated by 'gc_alloc'
void gc_free(void *ptr);

#endif /* GC_MALLOC_H */