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#ifndef ARENA_H
#define ARENA_H
//
// This module defines a simple, fixed-size arena allocator.
//
#include <stddef.h> // size_t
struct arena {
void *root;
size_t capacity;
size_t used;
};
// Initialize an arena with the given `capacity`.
// Panics on failure to allocate.
struct arena arena_create(size_t capacity);
// These flags control the behavior of `arena_alloc`.
#define ARENA_NO_ZERO 1
#define ARENA_NO_PANIC 2
// Allocate `size` bytes in `arena`.
// The resulting memory is zeroed unless ARENA_NO_ZERO is passed.
// Unless ARENA_NO_PANIC is specified, the resulting pointer is always valid.
void *arena_alloc(struct arena *arena, size_t size, size_t alignment, unsigned flags);
// Free the memory associated with the arena using the underlying allocator.
void arena_destroy(struct arena *arena);
//
// The `new` macro makes the basic allocation case simple. It uses a bit of
// preprocessor magic to simulate default argument values.
//
#define new(...) newx(__VA_ARGS__,new4,new3,new2)(__VA_ARGS__)
#define newx(a1, a2, a3, a4, a5, ...) a5
#define new2(arena, typ) (typ *)arena_alloc(arena, sizeof(typ), _Alignof(typ), 0)
#define new3(arena, typ, count) (typ *)arena_alloc(arena, count * sizeof(typ), _Alignof(typ), 0)
#define new4(arena, typ, count, flags) (typ *)arena_alloc(arena, count * sizeof(typ), _Alignof(typ), flags)
#endif
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