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/* Copyright (C) 2024 Aryadev Chavali
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Unlicense
* for details.
* You may distribute and modify this code under the terms of the
* Unlicense, which you should have received a copy of along with this
* program. If not, please go to <https://unlicense.org/>.
* Created: 2024-11-01
* Author: Aryadev Chavali
* Description: Arena allocator
*/
#ifndef ARENA_H
#define ARENA_H
#include <stdint.h>
struct Region;
typedef struct
{
struct Region *beg, *end;
} arena_t;
uint8_t *arena_alloc(arena_t *arena, uint32_t size);
uint8_t *arena_realloc(arena_t *arena, uint8_t *pointer, uint32_t old_size,
uint32_t new_size);
void arena_reset(arena_t *arena);
void arena_free(arena_t *arena);
#ifdef ARENA_IMPL
#include <malloc.h>
#include <string.h>
#ifndef REGION_DEFAULT_SIZE
#define REGION_DEFAULT_SIZE 512
#endif
#ifndef REGION_CAPACITY_MULT
#define REGION_CAPACITY_MULT 2
#endif
#define MAX(A, B) ((A) > (B) ? (A) : (B))
/**
@brief A single block of memory to be used by an arena.
@details Blocks of memory arranged in a singly linked list.
Each individual node is a bump allocator.
*/
typedef struct Region
{
struct Region *next;
uint32_t size, capacity;
uint8_t bytes[];
} region_t;
region_t *region_make(uint32_t capacity, region_t *next)
{
capacity = MAX(capacity, REGION_DEFAULT_SIZE);
region_t *region = calloc(1, sizeof(*region) + capacity);
region->next = next;
region->size = 0;
region->capacity = capacity;
return region;
}
uint8_t *region_alloc_rec(region_t *region, uint32_t capacity)
{
if (!region)
return NULL;
for (; region->next && region->capacity - region->size < capacity;
region = region->next)
continue;
if (region->capacity - region->size < capacity)
{
// no region->next, so make a new region that can fit the capacity required.
region_t *new = region_make(capacity * REGION_CAPACITY_MULT, NULL);
region->next = new;
region = new;
}
uint8_t *start = region->bytes + region->size;
region->size += capacity;
return start;
}
void region_delete(region_t *region)
{
while (region)
{
region_t *next = region->next;
free(region);
region = next;
}
}
uint8_t *arena_alloc(arena_t *arena, uint32_t size)
{
if (!arena->beg)
{
arena->beg = region_make(size, NULL);
arena->end = arena->beg;
}
uint8_t *start = region_alloc_rec(arena->beg, size);
// if we've attached a new region, end needs to be at that region
if (arena->end->next)
arena->end = arena->end->next;
return start;
}
uint8_t *arena_realloc(arena_t *arena, uint8_t *pointer, uint32_t old_size,
uint32_t new_size)
{
// Firstly find the region the pointer exists in
region_t *prev, *reg;
for (prev = NULL, reg = arena->beg;
reg &&
!(reg->bytes <= pointer && reg->bytes + reg->size >= pointer + old_size);
prev = reg, reg = reg->next)
continue;
if (!reg)
// pointer isn't allocated in the arena
return NULL;
uint8_t *new_ptr = NULL;
if (old_size == reg->size && reg->capacity == reg->size)
{
// Completely filled region, may as well reallocate
region_t *new_reg = region_make(new_size * REGION_CAPACITY_MULT, reg->next);
// Chain this new region in place
if (prev)
prev->next = new_reg;
if (reg == arena->end)
arena->end = new_reg;
free(reg);
new_ptr = new_reg->bytes;
new_reg->size += new_size;
}
else
{
// Allocate a new portion of memory on the arena
new_ptr = arena_alloc(arena, new_size);
}
memcpy(new_ptr, pointer, old_size);
return new_ptr;
}
void arena_free(arena_t *arena)
{
region_delete(arena->beg);
memset(arena, 0, sizeof(*arena));
}
#endif
#endif
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