GC.md

Mark and Sweep Garbage Collection system for Radiance

The existing malloc function needs to be modified to prepend the memory block with a GC header. This header contains a pointer to the next block, a flag indicating if it is "free" and the size of the block.

let start: i32 = 0

struct Header { is_free: bool size: u32 next: Header }

fn align_32 (size: u32) -> u32 { -(-size >> 2) << 2 }

fn align_64 (size: u32) -> u32 { -(-size >> 4) << 4 }

fn malloc (size: u32) -> u32 { let aligned_size = align_32(size) let header = find_free(aligned_size)

header.is_free = false
// block is much larger, split it
if header.size - aligned_size >= 16 {
	let next = unsafe { header as u32 } + 12
	next.next = header.next
	next.is_free = true
	next.size = header.size - (aligned_size + 12)
	header.next = next
	header.size = aligned_size 
}
return unsafe { header as u32 } + 12

}

fn free (ptr: u32) { let header = unsafe { (ptr - 12) as Header } let next = header.next header.is_free = true // join with next block if next.is_free { header.next = next.next header.size = header.size + next.size + 12 } }

fn find_free (size: u32): Header { let current: Header = unsafe { start as Header }

loop {
	if current.is_free and current.size >= size {
		return current
	}
	if current.next {
		current = current.next
	}
	else {
		break
	}
}

if (current.is_free) {
	grow((size - current.size) >> 16)

	current.size = current.size + PAGE_SIZE
	return current
}
else {
	grow(size >> 16)

	let next = unsafe { (current as u32 + current.size + 12) as Header }
	next.is_free = true
	next.next = null
	next.size = PAGE_SIZE - 12
	current.next = next
	return next
}

}