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#if PLATFORM_UNIX
internal MemArena *
unix_arena_create(u64 capacity)
{
MemArena *arena = (MemArena *)mmap(
/* kernel decides where to throw the arena */
NULL,
capacity + sizeof(MemArena),
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(MemArena);
arena->current_position = 0;
arena->previous_position = 0;
return arena;
}
internal void
unix_arena_destroy(MemArena *arena)
{
if(!arena)
{
return;
}
munmap(arena, arena->capacity + sizeof(MemArena));
}
#elif PLATFORM_WINDOWS
internal MemArena *
win32_arena_create(u64 capacity)
{
MemArena *arena = (MemArena *)VirtualAlloc(
NULL,
capacity + sizeof(MemArena),
MEM_COMMIT | MEM_RESERVE,
PAGE_READWRITE);
if(!arena)
{
return NULL;
}
arena->capacity = capacity;
arena->base_position = (u8 *)arena + sizeof(MemArena);
arena->current_position = 0;
arena->previous_position = 0;
return arena;
}
internal void
win32_arena_destroy(MemArena *arena)
{
if(!arena)
{
return;
}
VirtualFree(arena, 0, MEM_RELEASE);
return;
}
#endif
RETURNS_NON_NULL_VALUE internal void *
arena_alloc(MemArena *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)
{
MemSetZero(out, size);
}
return out;
}
internal void
arena_pop(MemArena *arena, u64 size)
{
size = Min(size, arena->current_position);
arena->current_position -= size;
}
internal void
arena_pop_to(MemArena *arena, u64 pos)
{
u64 size = pos < arena->current_position ? arena->current_position - pos : 0;
arena_pop(arena, size);
}
internal void
arena_clear(MemArena *arena)
{
arena->current_position = 0;
}
internal MemArena *
arena_resize_align(MemArena *arena, void *old_memory, u64 new_size, u64 old_size, umm alignment)
{
u8 *old_mem = (u8 *)old_memory;
if(is_pow(alignment))
{
arena->current_position = Align(arena->current_position, alignment);
}
if(old_memory == NULL || old_size == 0)
{
return (MemArena *)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 (MemArena *)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
{
// Log("yeah something in the mem allocator failed i guess"); // TODO: find a way to properly include the logging
}
return NULL;
}
internal MemArena *
arena_resize(MemArena *arena, void *old_memory, u64 new_size, u64 old_size)
{
return arena_resize_align(arena, old_memory, new_size, old_size, arena_align);
}
internal ScratchArena
scratch_start(MemArena *arena)
{
ScratchArena sa;
sa.arena = arena;
sa.start_position = arena->current_position;
return sa;
}
internal void
scratch_end(ScratchArena *sa)
{
sa->arena->current_position = sa->start_position;
}
//-
internal b32
is_pow(umm x)
{
return (x & (x - 1)) == 0;
}
internal u64
align(u64 pointer, umm alignment)
{
if((alignment & (alignment - 1)) == 0)
{
return pointer;
}
return (pointer + alignment - 1) & ~(alignment - 1);
}
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