arena.c

#include <assert.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>

#define KILO 1024
#define MEGA (1024 * KILO)
#define ARENA_CAPACITY 16

typedef struct Arena Arena;

struct Arena {
    Arena *next;
    size_t size;
    size_t capacity;
    uint8_t *memory;
};

Arena begin = {0};
Arena *current = &begin;

void *arena_alloc(size_t size)
{
    for (;;) {
        if (!current->memory) {
            current->capacity = size > ARENA_CAPACITY ? size : ARENA_CAPACITY;
            current->memory = calloc(1, current->capacity);
        }

        if (current->size + size <= current->capacity) {
            void *result = current->memory + current->size;
            current->size += size;
            return result;
        }

        if (!current->next) {
            current->next = calloc(1, sizeof(Arena));
        }

        current = current->next;
    }
}

void arena_clean(void)
{
    Arena *iter = &begin;
    while (iter) {
        iter->size = 0;
        iter = iter->next;
    }
    current = &begin;
}

void arena_print(void)
{
    Arena *iter = &begin;

    while (iter) {
        if (iter->memory) {
            for (size_t i = 0; i < iter->capacity; ++i) {
                printf("%02x ", iter->memory[i]);
            }
            printf("\n");
            for (size_t i = 0; i <= iter->capacity; ++i) {
                if (i == iter->size) {
                    printf("^  ");
                } else {
                    printf("   ");
                }
            }
            printf("\n");
        } else {
            printf("[Not initialized]\n");
        }

        iter = iter->next;
    }
    printf("------------------------------\n");
}

void test_alloc_n_ints(int n)
{
    int *xs = arena_alloc(sizeof(int) * n);
    for (int i = 0; i < n; ++i) xs[i] = i;
}

int main(int argc, char *argv[])
{
    test_alloc_n_ints(2);
    test_alloc_n_ints(8);
    arena_print();

    arena_clean();
    arena_print();

    test_alloc_n_ints(9);
    test_alloc_n_ints(2);
    arena_print();

    return 0;
}