ni-arena/niarena.h

#pragma once

#include "../ni-const/niconst.h"

// If custom memory management is provided, including this
// header can be skipped
#ifndef NIAREA_NO_STDLIB
#include <stdlib.h>
#endif

// The size can be defined by overriding this constant
#ifndef NIARENA_ARENA_SIZE
#define NIARENA_ARENA_SIZE NICONST_MIB_B(4)
#endif

// Custom memory management can be defined as well.
// Either both or none must be defined
#if (!defined(NIARENA_MALLOC) && defined(NIARENA_FREE)) || (defined(NIARENA_MALLOC) && !defined(NIARENA_FREE))
#error "Either both NIARENA_MALLOC and NIARENA_FREE have to be defined or neither of them"
#endif
#ifndef NIARENA_MALLOC
#define NIARENA_MALLOC(sz) malloc(sz)
#endif
#ifndef NIARENA_FREE
#define NIARENA_FREE(p) free(p)
#endif

// Definitions
typedef struct _NIArena {
	void *buffer;
	size_t capacity;
	size_t offset;
} NIArena;

const char *niarena_get_error(void);
NIArena *niarena_new(void);
void *niarena_alloc(NIArena *arena, size_t size);
void niarena_delete(NIArena *arena);

#ifdef NIARENA_IMPLEMENTATION

static const char *niarena__error_reason = "";

static void
niarena_error(const char *reason)
{
	niarena__error_reason = reason;
}

const char *
niarena_get_error(void)
{
	return niarena__error_reason;
}

NIArena *
niarena_new(void)
{
	NIArena *arena = NIARENA_MALLOC(sizeof(NIArena));
	if(arena == NULL) {
		niarena_error("niarena_new: out of memory allocating arena");
		return NULL;
	}
	arena->buffer = NIARENA_MALLOC(NIARENA_ARENA_SIZE);
	if(arena->buffer == NULL) {
		NIARENA_FREE(arena);
		niarena_error("niarena_new: out of memory allocating buffer");
		return NULL;
	}
	arena->capacity = NIARENA_ARENA_SIZE;
	return arena;
}

void *
niarena_alloc(NIArena *arena, size_t size)
{
	if((arena->capacity - arena->offset) < size) {
		// The allocation is invalid, but the contents of the arena
		// can still be used (previous allocations).
		niarena_error("niarena_alloc: out of memory inside of the arena");
		return NULL;
	}
	arena->offset += size;
	return (void *)((char *)arena->buffer + arena->offset);
}

void
niarena_delete(NIArena *arena)
{
	NIARENA_FREE(arena->buffer);
	NIARENA_FREE(arena);
}

#endif