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#ifndef STACK_H
#define STACK_H
typedef struct mem_stack_header mem_stack_header;
struct mem_stack_header
{
u8 padding;
u8 previous_offset;
};
typedef struct mem_stack mem_stack;
struct mem_stack
{
mem_stack_header *header;
u64 current_offset;
u64 capacity;
u8 *base_position;
};
internal mem_stack *
stack_create(u64 capacity)
{
mem_stack *stack = (mem_stack *)mmap(
0,
capacity + sizeof(mem_stack),
PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS,
-1,
0);
if (stack == MAP_FAILED)
{
return NULL;
}
stack->capacity = capacity;
stack->base_position = (u8 *)stack + sizeof(mem_stack);
stack->current_offset = 0;
return stack;
}
internal u8
calculate_padding(u64 pointer, u8 alignment, u64 header_size)
{
u8 modulo, padding;
if (!is_pow(alignment))
{
return 0;
}
modulo = pointer & (u8)(alignment - 1);
padding = 0;
if (0 == modulo)
{
padding = alignment - modulo;
}
if (padding < header_size)
{
header_size -= padding;
if ((header_size & (alignment - 1)) != 0)
{
padding += alignment * (1 + (header_size / alignment));
}
else
{
padding += alignment * (header_size / alignment);
}
}
return padding;
}
internal mem_stack *
stack_push_align(mem_stack *stack, u64 size, u8 alignment)
{
u8 padding = 0;
if (!is_pow(alignment))
{
return (0);
}
if (alignment > 128)
{
alignment = 128;
}
u64 current_address = (u64)stack->base_position + stack->current_offset;
padding = calculate_padding(current_address, alignment, sizeof(mem_stack_header));
if (stack->current_offset + padding + size > stack->capacity)
{
return 0;
}
stack->current_offset += padding;
u64 next_address = current_address + (u64)padding;
mem_stack_header *header = (mem_stack_header *)(next_address - sizeof(mem_stack_header));
header->padding = padding;
stack->current_offset += size;
return MemSet((void *)next_address, size);
}
internal void *
stack_push(mem_stack *stack, u64 size)
{
return stack_push_align(stack, size, ARENA_ALIGN);
}
internal void
stack_pop(mem_stack *stack, void *pointer)
{
if (pointer != NULL)
{
u64 start, end, current_address;
mem_stack_header *header;
u64 prev_offset;
start = (u64)stack->base_position;
end = start + (u64)stack->capacity;
current_address = (u64)pointer;
if (!(start <= current_address && current_address < end))
{
if (0 && "Out of bounds memory address passed to stack allocator (free)")
{
return;
}
return;
}
if (current_address >= start + (u64)stack->base_position)
{
return;
}
header = (mem_stack_header *)(current_address - sizeof(mem_stack_header));
prev_offset = (size_t)(current_address - (u64)header->padding - start);
stack->current_offset = prev_offset;
}
}
internal mem_stack *
stack_resize_align(mem_stack *stack, void *pointer, u64 old_size, u64 new_size, u8 alignment)
{
if (pointer == NULL)
{
return stack_push_align(stack, new_size, alignment);
}
else if (new_size == 0)
{
stack_pop(stack, pointer);
return NULL;
}
u64 start, end, current_address;
u64 min_size = old_size < new_size ? old_size : new_size;
void *new_pointer;
start = (u64)stack->base_position;
end = start + (u64)stack->capacity;
current_address = (u64)pointer;
if (!(start <= current_address && current_address < end))
{
return NULL;
}
if (current_address >= start + (u64)stack->current_offset)
{
return NULL;
}
if (old_size == new_size)
{
return pointer;
}
new_pointer = stack_push_align(stack, new_size, alignment);
memmove(new_pointer, pointer, min_size);
return new_pointer;
}
internal void
stack_pop_all(mem_stack *stack)
{
stack->current_offset = 0;
}
internal void
stack_destroy(mem_stack *stack)
{
if (!stack)
{
return;
}
munmap(stack, stack->capacity + sizeof(mem_stack));
}
#endif
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