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4 changed files with 93 additions and 21 deletions

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#ifndef GC_ALLOC_H
#define GC_ALLOC_H
#include <stdio.h>
// Metadata for allocated memory
struct gc_block_header {
size_t size;
int free;
struct gc_block_header *next;
};
// 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_ALLOC_H */

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include/gc_malloc.h Normal file
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#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 */

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#include "gc_alloc.h"

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src/gc_malloc.c Normal file
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#include <assert.h>
#include <stdint.h>
#include <sys/mman.h>
#include "gc_malloc.h"
// Hides chunk header
static inline void *hide(struct gc_chunk *curr)
{
return (void *)((uint64_t *)curr + MAGIC);
}
// Reveals chunk header
static inline struct gc_chunk *magic(void *mem)
{
return (struct gc_chunk *)((uint64_t *)mem - MAGIC);
}
// Aligns the amount of memory requested by the user with chunk size
static inline size_t align(size_t size)
{
const size_t alignment = 8;
size = (size + (alignment - 1)) & ~(alignment - 1);
if (size <= MIN)
return MIN;
else
return size;
}
struct gc_chunk *get_next_chunk(struct gc_chunk *curr)
{
unsigned size = curr->size;
return (struct gc_chunk *)((uint64_t *)curr + MAGIC + (size - 1));
}
struct gc_chunk *get_prev_chunk(struct gc_chunk *curr)
{
assert(curr->merge);
unsigned size = curr->footer;
return (struct gc_chunk *)((uint64_t *)curr - (size - 1) - MAGIC);
}