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internal mem_arena *
arena_create(u64 capacity)
{
mem_arena *arena = (mem_arena *)mmap(
/* kernel decides where to throw the arena */
NULL,
capacity + sizeof(mem_arena),
PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS,
-1,
0);
if (arena == MAP_FAILED)
{
return NULL;
}
arena->capacity = capacity;
arena->base_position = (u8 *)arena + sizeof(mem_arena);
arena->current_position = 0;
arena->previous_position = 0;
return arena;
}
internal void
arena_destroy(mem_arena *arena)
{
if (!arena)
{
return;
}
munmap(arena, arena->capacity + sizeof(mem_arena));
}
internal void *
arena_alloc(mem_arena *arena, u64 size, b32 zero)
{
if (!arena)
{
return NULL;
}
u64 aligned = Align(arena->current_position, ARENA_ALIGN);
u64 new_pos = aligned + size;
if (new_pos > arena->capacity)
{
return NULL;
}
void *out = arena->base_position + aligned;
arena->previous_position = arena->current_position;
arena->current_position = aligned + size;
if (zero) MemSet(out, size);
return out;
}
internal void
arena_pop(mem_arena *arena, u64 size)
{
size = MIN(size, arena->current_position);
arena->current_position -= size;
}
internal void
arena_pop_to(mem_arena *arena, u64 pos)
{
u64 size = pos < arena->current_position ? arena->current_position - pos : 0;
arena_pop(arena, size);
}
internal void
arena_clear(mem_arena *arena)
{
arena->current_position = 0;
}
internal mem_arena *
arena_resize_align(mem_arena *arena, void *old_memory, u64 new_size, u64 old_size, umm alignment)
{
u8 *old_mem = (u8 *)old_memory;
if (!is_pow(alignment))
{
Align(arena->current_position, alignment);
}
if (old_memory == NULL || old_size == 0)
{
return (mem_arena *)arena_alloc(arena, new_size, 0);
}
else if ((old_mem >= arena->base_position && old_mem < arena->base_position + arena->capacity))
{
if ((arena->base_position + arena->previous_position) == old_memory)
{
arena->current_position = arena->previous_position + new_size;
if (new_size > old_size)
{
MemSet(&arena->current_position, new_size - old_size);
}
return (mem_arena *)old_memory;
}
else
{
void *new_memory = arena_alloc(arena, new_size, 0);
umm copy_size = old_size < new_size ? old_size : new_size;
memmove(new_memory, old_mem, copy_size);
}
}
else
{
// warn(0);
}
return NULL;
}
internal mem_arena *
arena_resize(mem_arena *arena, void *old_memory, u64 new_size, u64 old_size)
{
return arena_resize_align(arena, old_memory, new_size, old_size, ARENA_ALIGN);
}
internal temp_arena
temp_arena_begin(mem_arena *arena)
{
temp_arena t;
t.arena = arena;
t.start_position = arena->current_position;
return t;
}
internal void
temp_arena_end(temp_arena temp)
{
temp.arena->current_position = temp.start_position;
}
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